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<title>XQuery 1.0: An XML Query Language (Second Edition)</title>

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<div class="head">
<p><a href="http://www.w3.org/"><img src=
"http://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width=
"72" /></a></p>
<h1><a name="title" id="title"></a>XQuery 1.0: An XML Query
Language (Second Edition)</h1>
<h2><a name="w3c-doctype" id="w3c-doctype"></a>W3C Recommendation
14 December 2010<em> (Link errors corrected 3 January 2011)</em></h2>
<dl>
<dt>This version:</dt>
<dd><span class="xquery"><a href=
"http://www.w3.org/TR/2010/REC-xquery-20101214/">http://www.w3.org/TR/2010/REC-xquery-20101214/</a></span></dd>
<dt>Latest version:</dt>
<dd><span class="xquery"><a href=
"http://www.w3.org/TR/xquery/">http://www.w3.org/TR/xquery/</a></span></dd>
<dt>Previous versions:</dt>
<dd><span class="xquery"><a href=
"http://www.w3.org/TR/2009/PER-xquery-20090421/">http://www.w3.org/TR/2009/PER-xquery-20090421/,</a></span>
<span class="xquery"><a href=
"http://www.w3.org/TR/2007/REC-xquery-20070123/">http://www.w3.org/TR/2007/REC-xquery-20070123/</a></span></dd>
<dt>Editors:</dt>
<dd>Scott Boag (XSL WG), IBM Research <a href=
"mailto:scott_boag@us.ibm.com">&lt;scott_boag@us.ibm.com&gt;</a></dd>
<dd>Don Chamberlin (XML Query WG) <a href=
"mailto:dchamber@us.ibm.com">&lt;dchamber@us.ibm.com&gt;</a></dd>
<dd>Mary F. Fernández (XML Query WG), AT&amp;T Labs <a href=
"mailto:mff@research.att.com">&lt;mff@research.att.com&gt;</a></dd>
<dd class="xquery">Daniela Florescu (XML Query WG), Oracle <a href=
"mailto:dana.florescu@oracle.com">&lt;dana.florescu@oracle.com&gt;</a></dd>
<dd>Jonathan Robie (XML Query WG), <span><a href=
"http://www.redhat.com">Red Hat</a></span>, via <a href=
"http://www.ibiblio.org/jwrobie/">http://www.ibiblio.org/jwrobie/</a></dd>
<dd>Jérôme Siméon (XML Query WG), IBM T.J. Watson Research Center
<a href=
"mailto:simeon@us.ibm.com">&lt;simeon@us.ibm.com&gt;</a></dd>
</dl>
<p>Please refer to the <a href=
"http://www.w3.org/XML/2010/qt-errata/xquery-errata2e.html"><strong>
errata</strong></a> for this document, which may include some
normative corrections.</p>
<p>See also <a href=
"http://www.w3.org/2003/03/Translations/byTechnology?technology=xquery">
<strong>translations</strong></a>.</p>
<p>This document is also available in these non-normative formats:
<span class="xquery"><a href=
"http://www.w3.org/TR/2010/REC-xquery-20101214/xquery-20101214.xml">
XML</a></span> and&#160;<span class="xquery"><a href=
"http://www.w3.org/TR/2010/REC-xquery-20101214/xquery-diff-from-REC20070123.html">Change
markings relative to first edition</a></span>.</p>
<p class="copyright"><a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>&#160;©&#160;2010&#160;<a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup>
(<a href="http://www.csail.mit.edu/"><acronym title=
"Massachusetts Institute of Technology">MIT</acronym></a>, <a href=
"http://www.ercim.eu/"><acronym title=
"European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved.
W3C <a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a href=
"http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
</div>
<hr />
<div>
<h2><a name="abstract" id="abstract"></a>Abstract</h2>
<div class="xquery">
<p class="xquery">XML is a versatile markup language, capable of
labeling the information content of diverse data sources including
structured and semi-structured documents, relational databases, and
object repositories. A query language that uses the structure of
XML intelligently can express queries across all these kinds of
data, whether physically stored in XML or viewed as XML via
middleware. This specification describes a query language called
XQuery, which is designed to be broadly applicable across many
types of XML data sources.</p>
</div>
</div>
<div>
<h2><a name="status" id="status"></a>Status of this Document</h2>
<p><em>This section describes the status of this document at the
time of its publication. Other documents may supersede this
document. A list of current W3C publications and the latest
revision of this technical report can be found in the <a href=
"http://www.w3.org/TR/">W3C technical reports index</a> at
http://www.w3.org/TR/.</em></p>
<p>This is one document in a set of eight documents that are being
progressed to Edited Recommendation together (XPath 2.0, XQuery
1.0, XQueryX 1.0, XSLT 2.0, Data Model (XDM), Functions and
Operators, Formal Semantics, Serialization).</p>
<p>This document, published on 14 December 2010, is an Edited
<a href=
"http://www.w3.org/2004/02/Process-20040205/tr.html#RecsW3C">Recommendation</a>
of the W3C. It supersedes the previous W3C Recommendation of 23
January 2007. This second edition is not a new version of this
specification; its purpose is to clarify a number of issues that
have become apparent since the first edition was published. All of
these clarifications (excepting trivial editorial fixes) have been
published in a separate errata document, and published in a
<a href="http://www.w3.org/2004/02/Process-20040205/tr.html#ProposedEditedRec">
Proposed Edited Recommendation</a> in April 2009. The changes are
summarized in an appendix. On 3 January 2011, the original
publication of this Recommendation was replaced by this version in
which two HTML anchors that were omitted by the original
publication have been restored; the W3C Team has retained a copy of
the original publication. This document <span class=
"xquery"><span class="xquery">has been developed by the W3C
<a href="http://www.w3.org/XML/Query/">XML Query Working Group</a>,
which is part of the <a href="http://www.w3.org/XML/Activity">XML
Activity</a>.</span></span></p>
<p>This document has been reviewed by W3C Members, by software
developers, and by other W3C groups and interested parties, and is
endorsed by the Director as a W3C Recommendation. It is a stable
document and may be used as reference material or cited from
another document. W3C's role in making the Recommendation is to
draw attention to the specification and to promote its widespread
deployment. This enhances the functionality and interoperability of
the Web.</p>
<p><span class="xquery"><span class="xquery">This document
incorporates changes made against the <a href=
"http://www.w3.org/2004/02/Process-20040205/tr.html#RecsW3C">Recommendation</a>
of 23 January 2007 that resolve all errata known at the date of
publication. Changes to this document since the first edition are
detailed in the <a href="#id-revisions-log"><b>K Changes since the
First Edition</b></a>. This document supersedes the <a href=
"http://www.w3.org/TR/2007/REC-xquery-20070123/">first
edition</a>.</span></span></p>
<div class="xquery">
<p class="xquery">An implementation report is available at <a href=
"http://www.w3.org/XML/Query/test-suite/XQTSReport.html">http://www.w3.org/XML/Query/test-suite/XQTSReport.html</a>.</p>
</div>
<p>Please report errors in and submit comments on this document
using W3C's <a href="http://www.w3.org/Bugs/Public/">public
Bugzilla system</a> (instructions can be found at <a href=
"http://www.w3.org/XML/2005/04/qt-bugzilla">http://www.w3.org/XML/2005/04/qt-bugzilla</a>).
If access to that system is not feasible, you may send your
comments to the W3C XSLT/XPath/XQuery public comments mailing list,
<a href=
"mailto:public-qt-comments@w3.org">public-qt-comments@w3.org</a>.
It will be very helpful if you include the string “<span class=
"xquery"><span class="xquery">[XQuery]</span></span>” in the
subject line of your report, whether made in Bugzilla or in email.
Each Bugzilla entry and email message should contain only one error
report. Archives of the comments and responses are available at
<a href=
"http://lists.w3.org/Archives/Public/public-qt-comments/">http://lists.w3.org/Archives/Public/public-qt-comments/</a>.</p>
<p>This document was produced by <span class="xquery"><span class=
"xquery">a group</span></span> operating under the <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
2004 W3C Patent Policy</a>. W3C maintains a <a href=
"http://www.w3.org/2004/01/pp-impl/18797/status#disclosures">public
list of any patent disclosures</a> made in connection with the
deliverables of the <span class="xquery"><span class=
"xquery">group; that page also includes</span></span> instructions
for disclosing a patent. An individual who has actual knowledge of
a patent which the individual believes contains <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">
Essential Claim(s)</a> must disclose the information in accordance
with <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">
section 6 of the W3C Patent Policy</a>.</p>
</div>
<div class="toc">
<h2><a name="contents" id="contents"></a>Table of Contents</h2>
<p class="toc">1 <a href="#id-introduction">Introduction</a><br />
2 <a href="#id-basics">Basics</a><br />
&#160;&#160;&#160;&#160;2.1 <a href="#context">Expression
Context</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.1.1 <a href=
"#static_context">Static Context</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.1.2 <a href=
"#eval_context">Dynamic Context</a><br />
&#160;&#160;&#160;&#160;2.2 <a href=
"#id-processing-model">Processing Model</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.1 <a href=
"#id-data-model-generation">Data Model Generation</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.2 <a href=
"#id-schema-import-processing">Schema Import Processing</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.3 <a href=
"#id-expression-processing">Expression Processing</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.3.1
<a href="#id-static-analysis">Static Analysis Phase</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.3.2
<a href="#id-dynamic-evaluation">Dynamic Evaluation Phase</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.4 <a href=
"#id-serialization">Serialization</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.2.5 <a href=
"#id-consistency-constraints">Consistency Constraints</a><br />
&#160;&#160;&#160;&#160;2.3 <a href="#errors">Error
Handling</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.3.1 <a href=
"#id-kinds-of-errors">Kinds of Errors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.3.2 <a href=
"#id-identifying-errors">Identifying and Reporting Errors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.3.3 <a href=
"#id-handling-dynamic">Handling Dynamic Errors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.3.4 <a href=
"#id-errors-and-opt">Errors and Optimization</a><br />
&#160;&#160;&#160;&#160;2.4 <a href=
"#id-important-concepts">Concepts</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.4.1 <a href=
"#id-document-order">Document Order</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.4.2 <a href=
"#id-atomization">Atomization</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.4.3 <a href=
"#id-ebv">Effective Boolean Value</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.4.4 <a href=
"#id-input-sources">Input Sources</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.4.5 <a href=
"#id-uri-literals">URI Literals</a><br />
&#160;&#160;&#160;&#160;2.5 <a href="#id-types">Types</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.1 <a href=
"#id-predefined-types">Predefined Schema Types</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.2 <a href=
"#id-typed-value">Typed Value and String Value</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.3 <a href=
"#id-sequencetype-syntax">SequenceType Syntax</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4 <a href=
"#id-sequencetype-matching">SequenceType Matching</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4.1
<a href="#id-matching-value">Matching a SequenceType and a
Value</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4.2
<a href="#id-matching-item">Matching an ItemType and an
Item</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4.3
<a href="#id-element-test">Element Test</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4.4
<a href="#id-schema-element-test">Schema Element Test</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4.5
<a href="#id-attribute-test">Attribute Test</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;2.5.4.6
<a href="#id-schema-attribute-test">Schema Attribute Test</a><br />
&#160;&#160;&#160;&#160;2.6 <a href="#comments">Comments</a><br />
3 <a href="#id-expressions">Expressions</a><br />
&#160;&#160;&#160;&#160;3.1 <a href=
"#id-primary-expressions">Primary Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.1.1 <a href=
"#id-literals">Literals</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.1.2 <a href=
"#id-variables">Variable References</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.1.3 <a href=
"#id-paren-expressions">Parenthesized Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.1.4 <a href=
"#id-context-item-expression">Context Item Expression</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.1.5 <a href=
"#id-function-calls">Function Calls</a><br />
&#160;&#160;&#160;&#160;3.2 <a href="#id-path-expressions">Path
Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.2.1 <a href=
"#id-steps">Steps</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.2.1.1
<a href="#axes">Axes</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.2.1.2
<a href="#node-tests">Node Tests</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.2.2 <a href=
"#id-predicates">Predicates</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.2.3 <a href=
"#unabbrev">Unabbreviated Syntax</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.2.4 <a href=
"#abbrev">Abbreviated Syntax</a><br />
&#160;&#160;&#160;&#160;3.3 <a href=
"#id-sequence-expressions">Sequence Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.3.1 <a href=
"#construct_seq">Constructing Sequences</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.3.2 <a href=
"#id-filter-expr">Filter Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.3.3 <a href=
"#combining_seq">Combining Node Sequences</a><br />
&#160;&#160;&#160;&#160;3.4 <a href="#id-arithmetic">Arithmetic
Expressions</a><br />
&#160;&#160;&#160;&#160;3.5 <a href="#id-comparisons">Comparison
Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.5.1 <a href=
"#id-value-comparisons">Value Comparisons</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.5.2 <a href=
"#id-general-comparisons">General Comparisons</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.5.3 <a href=
"#id-node-comparisons">Node Comparisons</a><br />
&#160;&#160;&#160;&#160;3.6 <a href=
"#id-logical-expressions">Logical Expressions</a><br />
&#160;&#160;&#160;&#160;3.7 <a href=
"#id-constructors">Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.1 <a href=
"#id-element-constructor">Direct Element Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.1.1
<a href="#id-attributes">Attributes</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.1.2
<a href="#id-namespaces">Namespace Declaration Attributes</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.1.3
<a href="#id-content">Content</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.1.4
<a href="#id-whitespace">Boundary Whitespace</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.2 <a href=
"#id-otherConstructors">Other Direct Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3 <a href=
"#id-computedConstructors">Computed Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3.1
<a href="#id-computedElements">Computed Element
Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3.2
<a href="#id-computedAttributes">Computed Attribute
Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3.3
<a href="#id-documentConstructors">Document Node
Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3.4
<a href="#id-textConstructors">Text Node Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3.5
<a href="#id-computed-pis">Computed Processing Instruction
Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.3.6
<a href="#id-computed-comments">Computed Comment
Constructors</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.7.4 <a href=
"#id-ns-nodes-on-elements">In-scope Namespaces of a Constructed
Element</a><br />
&#160;&#160;&#160;&#160;3.8 <a href="#id-flwor-expressions">FLWOR
Expressions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.8.1 <a href=
"#id-for-let">For and Let Clauses</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.8.2 <a href=
"#id-where">Where Clause</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.8.3 <a href=
"#id-orderby-return">Order By and Return Clauses</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.8.4 <a href=
"#id-flwor-example">Example</a><br />
&#160;&#160;&#160;&#160;3.9 <a href=
"#id-unordered-expressions">Ordered and Unordered
Expressions</a><br />
&#160;&#160;&#160;&#160;3.10 <a href="#id-conditionals">Conditional
Expressions</a><br />
&#160;&#160;&#160;&#160;3.11 <a href=
"#id-quantified-expressions">Quantified Expressions</a><br />
&#160;&#160;&#160;&#160;3.12 <a href=
"#id-expressions-on-datatypes">Expressions on
SequenceTypes</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.12.1 <a href=
"#id-instance-of">Instance Of</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.12.2 <a href=
"#id-typeswitch">Typeswitch</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.12.3 <a href=
"#id-cast">Cast</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.12.4 <a href=
"#id-castable">Castable</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.12.5 <a href=
"#id-constructor-functions">Constructor Functions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;3.12.6 <a href=
"#id-treat">Treat</a><br />
&#160;&#160;&#160;&#160;3.13 <a href="#id-validate">Validate
Expressions</a><br />
&#160;&#160;&#160;&#160;3.14 <a href=
"#id-extension-expressions">Extension Expressions</a><br />
4 <a href="#id-query-prolog">Modules and Prologs</a><br />
&#160;&#160;&#160;&#160;4.1 <a href=
"#id-version-declaration">Version Declaration</a><br />
&#160;&#160;&#160;&#160;4.2 <a href="#id-module-declaration">Module
Declaration</a><br />
&#160;&#160;&#160;&#160;4.3 <a href=
"#id-boundary-space-decls">Boundary-space Declaration</a><br />
&#160;&#160;&#160;&#160;4.4 <a href=
"#id-default-collation-declaration">Default Collation
Declaration</a><br />
&#160;&#160;&#160;&#160;4.5 <a href="#id-base-uri-decl">Base URI
Declaration</a><br />
&#160;&#160;&#160;&#160;4.6 <a href=
"#id-construction-declaration">Construction Declaration</a><br />
&#160;&#160;&#160;&#160;4.7 <a href=
"#id-default-ordering-decl">Ordering Mode Declaration</a><br />
&#160;&#160;&#160;&#160;4.8 <a href="#id-empty-order-decl">Empty
Order Declaration</a><br />
&#160;&#160;&#160;&#160;4.9 <a href=
"#id-copy-namespaces-decl">Copy-Namespaces Declaration</a><br />
&#160;&#160;&#160;&#160;4.10 <a href="#id-schema-import">Schema
Import</a><br />
&#160;&#160;&#160;&#160;4.11 <a href="#id-module-import">Module
Import</a><br />
&#160;&#160;&#160;&#160;4.12 <a href=
"#id-namespace-declaration">Namespace Declaration</a><br />
&#160;&#160;&#160;&#160;4.13 <a href=
"#id-default-namespace">Default Namespace Declaration</a><br />
&#160;&#160;&#160;&#160;4.14 <a href=
"#id-variable-declarations">Variable Declaration</a><br />
&#160;&#160;&#160;&#160;4.15 <a href="#FunctionDeclns">Function
Declaration</a><br />
&#160;&#160;&#160;&#160;4.16 <a href=
"#id-option-declaration">Option Declaration</a><br />
5 <a href="#id-xquery-conformance">Conformance</a><br />
&#160;&#160;&#160;&#160;5.1 <a href=
"#id-minimal-conformance">Minimal Conformance</a><br />
&#160;&#160;&#160;&#160;5.2 <a href=
"#id-conform-optional-features">Optional Features</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.1 <a href=
"#id-schema-import-feature">Schema Import Feature</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.2 <a href=
"#id-schema-validation-feature">Schema Validation Feature</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.3 <a href=
"#id-static-typing-feature">Static Typing Feature</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.3.1
<a href="#id-static-extensions">Static Typing Extensions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.4 <a href=
"#id-full-axis-feature">Full Axis Feature</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.5 <a href=
"#id-module-feature">Module Feature</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;5.2.6 <a href=
"#id-serialization-feature">Serialization Feature</a><br />
&#160;&#160;&#160;&#160;5.3 <a href=
"#id-data-model-conformance">Data Model Conformance</a><br />
&#160;&#160;&#160;&#160;5.4 <a href="#id-syntax-extensions">Syntax
Extensions</a><br /></p>
<h3><a name="appendices" id="appendices"></a>Appendices</h3>
<p class="toc">A <a href="#nt-bnf">XQuery Grammar</a><br />
&#160;&#160;&#160;&#160;A.1 <a href="#id-grammar">EBNF</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.1.1 <a href=
"#EBNFNotation">Notation</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.1.2 <a href=
"#extra-grammatical-constraints">Extra-grammatical
Constraints</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.1.3 <a href=
"#notes-on-parsing">Grammar Notes</a><br />
&#160;&#160;&#160;&#160;A.2 <a href="#lexical-structure">Lexical
structure</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.1 <a href=
"#terminal-symbols">Terminal Symbols</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.2 <a href=
"#id-terminal-delimitation">Terminal Delimitation</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.3 <a href=
"#id-eol-handling">End-of-Line Handling</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.3.1
<a href="#id-xml10-eol-handling">XML 1.0 End-of-Line
Handling</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.3.2
<a href="#id-xml11-eol-handling">XML 1.1 End-of-Line
Handling</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.4 <a href=
"#whitespace-rules">Whitespace Rules</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.4.1
<a href="#DefaultWhitespaceHandling">Default Whitespace
Handling</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;A.2.4.2
<a href="#ExplicitWhitespaceHandling">Explicit Whitespace
Handling</a><br />
&#160;&#160;&#160;&#160;A.3 <a href=
"#id-reserved-fn-names">Reserved Function Names</a><br />
&#160;&#160;&#160;&#160;A.4 <a href=
"#id-precedence-order">Precedence Order</a><br />
B <a href="#id-type-promotion-and-operator-mapping">Type Promotion
and Operator Mapping</a><br />
&#160;&#160;&#160;&#160;B.1 <a href="#promotion">Type
Promotion</a><br />
&#160;&#160;&#160;&#160;B.2 <a href="#mapping">Operator
Mapping</a><br />
C <a href="#id-xq-context-components">Context Components</a><br />
&#160;&#160;&#160;&#160;C.1 <a href=
"#id-xq-static-context-components">Static Context
Components</a><br />
&#160;&#160;&#160;&#160;C.2 <a href=
"#id-xq-evaluation-context-components">Dynamic Context
Components</a><br />
&#160;&#160;&#160;&#160;C.3 <a href=
"#id-xq-serialization-parameters">Serialization
Parameters</a><br />
D <a href="#id-impl-defined-items">Implementation-Defined
Items</a><br />
E <a href="#id-references">References</a><br />
&#160;&#160;&#160;&#160;E.1 <a href=
"#id-normative-references">Normative References</a><br />
&#160;&#160;&#160;&#160;E.2 <a href=
"#id-non-normative-references">Non-normative References</a><br />
&#160;&#160;&#160;&#160;E.3 <a href=
"#id-background-material">Background Material</a><br />
F <a href="#id-errors">Error Conditions</a><br />
G <a href="#id-mime-type">The application/xquery Media
Type</a><br />
&#160;&#160;&#160;&#160;G.1 <a href=
"#id-mime-type-intro">Introduction</a><br />
&#160;&#160;&#160;&#160;G.2 <a href=
"#id-registration-of-mime-type">Registration of MIME Media Type
application/xquery</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;G.2.1 <a href=
"#id-interoperability-considerations">Interoperability
Considerations</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;G.2.2 <a href=
"#id-published-specification">Published specification</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;G.2.3 <a href=
"#id-applications-of-media-type">Applications Using this Media
Type</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;G.2.4 <a href=
"#id-file-extensions">File Extensions</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;G.2.5 <a href=
"#id-intended-usage">Intended Usage</a><br />
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;G.2.6 <a href=
"#id-author-change-controller">Author/Change Controller</a><br />
&#160;&#160;&#160;&#160;G.3 <a href=
"#xquery-mime-encoding">Encoding Considerations</a><br />
&#160;&#160;&#160;&#160;G.4 <a href=
"#xquery-mime-recognizing">Recognizing XQuery Files</a><br />
&#160;&#160;&#160;&#160;G.5 <a href=
"#id-charset-default-rules">Charset Default Rules</a><br />
&#160;&#160;&#160;&#160;G.6 <a href=
"#id-security-considerations">Security Considerations</a><br />
H <a href="#id-glossary">Glossary</a> (Non-Normative)<br />
I <a href="#id-example-applications">Example Applications</a>
(Non-Normative)<br />
&#160;&#160;&#160;&#160;I.1 <a href="#id-joins">Joins</a><br />
&#160;&#160;&#160;&#160;I.2 <a href=
"#id-grouping">Grouping</a><br />
&#160;&#160;&#160;&#160;I.3 <a href=
"#id-queries-on-sequence">Queries on Sequence</a><br />
&#160;&#160;&#160;&#160;I.4 <a href=
"#id-recursive-transformations">Recursive Transformations</a><br />
&#160;&#160;&#160;&#160;I.5 <a href="#id-select-distinct">Selecting
Distinct Combinations</a><br />
J <a href="#id-module-handling">Guidance for Handling of
Modules</a> (Non-Normative)<br />
&#160;&#160;&#160;&#160;J.1 <a href=
"#id-module-handling-module-uris">Module URIs</a><br />
&#160;&#160;&#160;&#160;J.2 <a href=
"#id-module-handling-multiple-same">Multiple Modules with the same
Module URI</a><br />
&#160;&#160;&#160;&#160;J.3 <a href=
"#id-module-handling-location-uris">Location URIs</a><br />
&#160;&#160;&#160;&#160;J.4 <a href=
"#id-module-handling-cycles">Cycles</a><br />
K <a href="#id-revisions-log">Changes since the First Edition</a>
(Non-Normative)<br /></p>
</div>
<hr />
<div class="body">
<div class="div1">
<h2><a name="id-introduction" id="id-introduction"></a>1
Introduction</h2>
<div class="xquery">
<p class="xquery">As increasing amounts of information are stored,
exchanged, and presented using XML, the ability to intelligently
query XML data sources becomes increasingly important. One of the
great strengths of XML is its flexibility in representing many
different kinds of information from diverse sources. To exploit
this flexibility, an XML query language must provide features for
retrieving and interpreting information from these diverse
sources.</p>
</div>
<div class="xquery">
<p class="xquery">XQuery is designed to meet the requirements
identified by the W3C XML Query Working Group <a href=
"#Requirements">[XML Query 1.0 Requirements]</a> and the use cases
in <a href="#UseCases">[XML Query Use Cases]</a>. It is designed to
be a language in which queries are concise and easily understood.
It is also flexible enough to query a broad spectrum of XML
information sources, including both databases and documents. The
Query Working Group has identified a requirement for both a non-XML
query syntax and an XML-based query syntax. XQuery is designed to
meet the first of these requirements. XQuery is derived from an XML
query language called Quilt <a href="#Quilt">[Quilt]</a>, which in
turn borrowed features from several other languages, including
XPath 1.0 <a href="#XPath">[XPath 1.0]</a>, XQL <a href=
"#XQL">[XQL]</a>, XML-QL <a href="#XML-QL">[XML-QL]</a>, SQL
<a href="#SQL">[SQL]</a>, and OQL <a href="#ODMG">[ODMG]</a>.</p>
</div>
<p>[<a name="dt-datamodel" id="dt-datamodel" title=
"data model">Definition</a>: XQuery operates on the abstract,
logical structure of an XML document, rather than its surface
syntax. This logical structure, known as the <b>data model</b>, is
defined in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data
Model (Second Edition)]</a>.]</p>
<p>XQuery Version 1.0 is an extension of XPath Version 2.0. Any
expression that is syntactically valid and executes successfully in
both XPath 2.0 and XQuery 1.0 will return the same result in both
languages. Since these languages are so closely related, their
grammars and language descriptions are generated from a common
source to ensure consistency, and the editors of these
specifications work together closely.</p>
<p>XQuery also depends on and is closely related to the following
specifications:</p>
<ul>
<li>
<p><a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data Model
(Second Edition)]</a> defines the data model that underlies all
XQuery expressions.</p>
</li>
<li>
<p><a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0
Formal Semantics (Second Edition)]</a> defines the static semantics
of XQuery and also contains a formal but non-normative description
of the dynamic semantics that may be useful for implementors and
others who require a formal definition.</p>
</li>
<li>
<p>The type system of XQuery is based on <a href="#XMLSchema">[XML
Schema]</a>.</p>
</li>
<li>
<p>The built-in function library and the operators supported by
XQuery are defined in <a href="#FunctionsAndOperators">[XQuery 1.0
and XPath 2.0 Functions and Operators (Second Edition)]</a>.</p>
</li>
<li class="xquery">
<p>One requirement in <a href="#Requirements">[XML Query 1.0
Requirements]</a> is that an XML query language have both a
human-readable syntax and an XML-based syntax. The XML-based syntax
for XQuery is described in <a href="#XQueryX">[XML Syntax for
XQuery 1.0 (XQueryX) (Second Edition)]</a>.</p>
</li>
</ul>
<p>This document specifies a grammar for XQuery, using the same
basic EBNF notation used in <a href="#XML">[XML 1.0]</a>. Unless
otherwise noted (see <a href="#lexical-structure"><b>A.2 Lexical
structure</b></a>), whitespace is not significant in <span class=
"xquery"><span class="xquery">queries</span></span>. Grammar
productions are introduced together with the features that they
describe, and a complete grammar is also presented in the appendix
[<a href="#nt-bnf"><b>A XQuery Grammar</b></a>]. The appendix is
the normative version.</p>
<p>In the grammar productions in this document, named symbols are
underlined and literal text is enclosed in double quotes. For
example, the following production describes the syntax of a
function call:</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="fakeid_doc-xquery-FunctionCall" id=
"fakeid_doc-xquery-FunctionCall"></a>[93]&#160;&#160;&#160;</td>
<td><code>FunctionCall</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a> "(" (<a href=
"#doc-xquery-ExprSingle">ExprSingle</a> ("," <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>)*)? ")"</code></td>
</tr>
</tbody>
</table>
<p>The production should be read as follows: A function call
consists of a QName followed by an open-parenthesis. The
open-parenthesis is followed by an optional argument list. The
argument list (if present) consists of one or more expressions,
separated by commas. The optional argument list is followed by a
close-parenthesis.</p>
<p>Certain aspects of language processing are described in this
specification as <b>implementation-defined</b> or
<b>implementation-dependent</b>.</p>
<ul>
<li>
<p>[<a name="dt-implementation-defined" id=
"dt-implementation-defined" title=
"implementation defined">Definition</a>:
<b>Implementation-defined</b> indicates an aspect that may differ
between implementations, but must be specified by the implementor
for each particular implementation.]</p>
</li>
<li>
<p>[<a name="dt-implementation-dependent" id=
"dt-implementation-dependent" title=
"implementation dependent">Definition</a>:
<b>Implementation-dependent</b> indicates an aspect that may differ
between implementations, is not specified by this or any W3C
specification, and is not required to be specified by the
implementor for any particular implementation.]</p>
</li>
</ul>
<p>This document normatively defines the dynamic semantics of
XQuery. The static semantics of XQuery are normatively defined in
<a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal
Semantics (Second Edition)]</a>. In this document, examples and
material labeled as "Note" are provided for explanatory purposes
and are not normative.</p>
</div>
<div class="div1">
<h2><a name="id-basics" id="id-basics"></a>2 Basics</h2>
<p>The basic building block of XQuery is the <b>expression</b>,
which is a string of <a href="#Unicode">[Unicode]</a> characters
(the version of Unicode to be used is <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.) The
language provides several kinds of expressions which may be
constructed from keywords, symbols, and operands. In general, the
operands of an expression are other expressions. XQuery allows
expressions to be nested with full generality. <span class=
"xquery"><span class="xquery">(However, unlike a pure functional
language, it does not allow variable substitution if the variable
declaration contains construction of new nodes.)</span></span></p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>This specification contains no assumptions or requirements
regarding the character set encoding of strings of <a href=
"#Unicode">[Unicode]</a> characters.</p>
</div>
<p>Like XML, XQuery is a case-sensitive language. Keywords in
XQuery use lower-case characters and are not reserved—that is,
names in XQuery expressions are allowed to be the same as language
keywords, except for certain unprefixed function-names listed in
<a href="#id-reserved-fn-names"><b>A.3 Reserved Function
Names</b></a>.</p>
<p>[<a name="dt-value" id="dt-value" title="value">Definition</a>:
In the <a title="data model" href="#dt-datamodel">data model</a>, a
<b>value</b> is always a <a title="sequence" href=
"#dt-sequence">sequence</a>.] [<a name="dt-sequence" id=
"dt-sequence" title="sequence">Definition</a>: A <b>sequence</b> is
an ordered collection of zero or more <a title="item" href=
"#dt-item">items</a>.] [<a name="dt-item" id="dt-item" title=
"item">Definition</a>: An <b>item</b> is either an <a title=
"atomic value" href="#dt-atomic-value">atomic value</a> or a
<a title="node" href="#dt-node">node</a>.] [<a name=
"dt-atomic-value" id="dt-atomic-value" title=
"atomic value">Definition</a>: An <b>atomic value</b> is a value in
the value space of an <b>atomic type</b>, as defined in <a href=
"#XMLSchema">[XML Schema]</a>.] [<a name="dt-node" id="dt-node"
title="node">Definition</a>: A <b>node</b> is an instance of one of
the <b>node kinds</b> defined in <a href="#datamodel">[XQuery 1.0
and XPath 2.0 Data Model (Second Edition)]</a>.] Each node has a
unique <b>node identity</b>, a <b>typed value</b>, and a <b>string
value</b>. In addition, some nodes have a <b>name</b>. The <b>typed
value</b> of a node is a sequence of zero or more atomic values.
The <b>string value</b> of a node is a value of type
<code>xs:string</code>. The <b>name</b> of a node is a value of
type <code>xs:QName</code>. [<a name="dt-undefined" id=
"dt-undefined" title="undefined">Definition</a>: In certain
situations a value is said to be <b>undefined</b> (for example, the
value of the context item, or the typed value of an element node).
This term indicates that the property in question has no value and
that any attempt to use its value results in an error.]</p>
<p>[<a name="dt-singleton" id="dt-singleton" title=
"singleton">Definition</a>: A sequence containing exactly one item
is called a <b>singleton</b>.] An item is identical to a singleton
sequence containing that item. Sequences are never nested—for
example, combining the values 1, (2, 3), and ( ) into a single
sequence results in the sequence (1, 2, 3). [<a name=
"dt-empty-sequence" id="dt-empty-sequence" title=
"empty sequence">Definition</a>: A sequence containing zero items
is called an <b>empty sequence</b>.]</p>
<p>[<a name="dt-data-model-instance" id="dt-data-model-instance"
title="XDM instance">Definition</a>: The term <b>XDM instance</b>
is used, synonymously with the term <b>value</b>, to denote an
unconstrained sequence of <a title="node" href="#dt-node">nodes</a>
and/or <a title="atomic value" href="#dt-atomic-value">atomic
values</a> in the <a title="data model" href="#dt-datamodel">data
model</a>.]</p>
<p>Names in XQuery are called <b>QNames</b>, and conform to the
syntax in <a href="#XMLNAMES">[XML Names]</a>. [<a name="dt-qname"
id="dt-qname" title="QName">Definition</a>: Lexically, a
<b>QName</b> consists of an optional namespace prefix and a local
name. If the namespace prefix is present, it is separated from the
local name by a colon.] A lexical QName can be converted into an
<b>expanded QName</b> by resolving its namespace prefix to a
namespace URI, using the <a title="statically known namespaces"
href="#dt-static-namespaces">statically known namespaces</a>
[<a href="#ERRXPST0081" title="err:XPST0081">err:XPST0081</a>].
[<a name="dt-expanded-qname" id="dt-expanded-qname" title=
"expanded QName">Definition</a>: An <b>expanded QName</b> consists
of an optional namespace URI and a local name. An expanded QName
also retains its original namespace prefix (if any), to facilitate
casting the expanded QName into a string.] The namespace URI value
is whitespace normalized according to the rules for the
<code>xs:anyURI</code> type in <a href="#XMLSchema">[XML
Schema]</a>. Two expanded QNames are equal if their namespace URIs
are equal and their local names are equal (even if their namespace
prefixes are not equal). Namespace URIs and local names are
compared on a codepoint basis, without further normalization.</p>
<div class="xquery">
<p class="xquery">Certain namespace prefixes are predeclared by
XQuery and bound to fixed namespace URIs. These namespace prefixes
are as follows:</p>
</div>
<ul>
<li class="xquery">
<p><code>xml = http://www.w3.org/XML/1998/namespace</code></p>
</li>
<li>
<p><code>xs = http://www.w3.org/2001/XMLSchema</code></p>
</li>
<li class="xquery">
<p><code>xsi = http://www.w3.org/2001/XMLSchema-instance</code></p>
</li>
<li>
<p><code>fn = http://www.w3.org/2005/xpath-functions</code></p>
</li>
<li class="xquery">
<p><code>local =
http://www.w3.org/2005/xquery-local-functions</code> (see <a href=
"#FunctionDeclns"><b>4.15 Function Declaration</b></a>.)</p>
</li>
</ul>
<div class="xquery">
<p class="xquery">In addition to the prefixes in the above list,
this document uses the prefix <code>err</code> to represent the
namespace URI <code>http://www.w3.org/2005/xqt-errors</code> (see
<a href="#id-identifying-errors"><b>2.3.2 Identifying and Reporting
Errors</b></a>). This namespace prefix is not predeclared and its
use in this document is not normative.</p>
</div>
<p>Element nodes have a property called <b>in-scope namespaces</b>.
[<a name="dt-in-scope-namespaces" id="dt-in-scope-namespaces"
title="in-scope namespaces">Definition</a>: The <b>in-scope
namespaces</b> property of an element node is a set of <b>namespace
bindings</b>, each of which associates a namespace prefix with a
URI, thus defining the set of namespace prefixes that are available
for interpreting QNames within the scope of the element. For a
given element, one namespace binding may have an empty prefix; the
URI of this namespace binding is the default namespace within the
scope of the element.]</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>In <a href="#XPath">[XPath 1.0]</a>, the in-scope namespaces of
an element node are represented by a collection of <b>namespace
nodes</b> arranged on a <b>namespace axis</b>, which is optional
and deprecated in <a href="#XPath20">[XML Path Language (XPath) 2.0
(Second Edition)]</a>. XQuery does not support the namespace axis
and does not represent namespace bindings in the form of nodes.
However, where other specifications such as <a href=
"#serialization">[XSLT 2.0 and XQuery 1.0 Serialization (Second
Edition)]</a> refer to namespace nodes, these nodes may be
synthesized from the in-scope namespaces of an element node by
interpreting each namespace binding as a namespace node.</p>
</div>
<p>[<a name="dt-URI" id="dt-URI" title="URI">Definition</a>: Within
this specification, the term <b>URI</b> refers to a Universal
Resource Identifier as defined in <a href="#RFC3986">[RFC3986]</a>
and extended in <a href="#RFC3987">[RFC3987]</a> with the new name
<b>IRI</b>.] The term URI has been retained in preference to IRI to
avoid introducing new names for concepts such as "Base URI" that
are defined or referenced across the whole family of XML
specifications.</p>
<div class="div2">
<h3><a name="context" id="context"></a>2.1 Expression Context</h3>
<p>[<a name="dt-expression-context" id="dt-expression-context"
title="expression context">Definition</a>: The <b>expression
context</b> for a given expression consists of all the information
that can affect the result of the expression.] This information is
organized into two categories called the <a title="static context"
href="#dt-static-context">static context</a> and the <a title=
"dynamic context" href="#dt-dynamic-context">dynamic
context</a>.</p>
<div class="div3">
<h4><a name="static_context" id="static_context"></a>2.1.1 Static
Context</h4>
<p>[<a name="dt-static-context" id="dt-static-context" title=
"static context">Definition</a>: The <b>static context</b> of an
expression is the information that is available during static
analysis of the expression, prior to its evaluation.] This
information can be used to decide whether the expression contains a
<a title="static error" href="#dt-static-error">static error</a>.
If analysis of an expression relies on some component of the
<a title="static context" href="#dt-static-context">static
context</a> that has not been assigned a value, a <a title=
"static error" href="#dt-static-error">static error</a> is raised
[<a href="#ERRXPST0001" title="err:XPST0001">err:XPST0001</a>].</p>
<p>The individual components of the <a title="static context" href=
"#dt-static-context">static context</a> are summarized below.
<span class="xquery"><span class="xquery">Rules governing the scope
and initialization of these components can be found in <a href=
"#id-xq-static-context-components"><b>C.1 Static Context
Components</b></a>.</span></span></p>
<ul>
<li>
<p>[<a name="dt-xpath-compat-mode" id="dt-xpath-compat-mode" title=
"XPath 1.0 compatibility mode">Definition</a>: <b>XPath 1.0
compatibility mode.</b> <span class="xquery"><span class=
"xquery">This component must be set by all host languages that
include XPath 2.0 as a subset, indicating whether rules for
compatibility with XPath 1.0 are in effect. XQuery sets the value
of this component to <code>false</code>.</span></span> ]</p>
</li>
<li>
<p>[<a name="dt-static-namespaces" id="dt-static-namespaces" title=
"statically known namespaces">Definition</a>: <b>Statically known
namespaces.</b> This is a set of (prefix, URI) pairs that define
all the namespaces that are known during static processing of a
given expression.] The URI value is whitespace normalized according
to the rules for the <code>xs:anyURI</code> type in <a href=
"#XMLSchema">[XML Schema]</a>. Note the difference between
<a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a>, which is a
dynamic property of an element node, and <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>, which is a
static property of an expression.</p>
<div class="xquery">
<p class="xquery">Some namespaces are predefined; additional
namespaces can be added to the statically known namespaces by
<a title="namespace declaration" href=
"#dt-namespace-declaration">namespace declarations</a> in a
<a title="Prolog" href="#dt-prolog">Prolog</a> and by <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attributes</a> in
<a title="direct element constructor" href=
"#dt-direct-elem-const">direct element constructors</a>.</p>
</div>
</li>
<li>
<p>[<a name="dt-def-elemtype-ns" id="dt-def-elemtype-ns" title=
"default element/type namespace">Definition</a>: <b>Default
element/type namespace.</b> This is a namespace URI or "none". The
namespace URI, if present, is used for any unprefixed QName
appearing in a position where an element or type name is expected.]
The URI value is whitespace normalized according to the rules for
the <code>xs:anyURI</code> type in <a href="#XMLSchema">[XML
Schema]</a>.</p>
</li>
<li>
<p>[<a name="dt-def-fn-ns" id="dt-def-fn-ns" title=
"default function namespace">Definition</a>: <b>Default function
namespace.</b> This is a namespace URI or "none". The namespace
URI, if present, is used for any unprefixed QName appearing in a
position where a function name is expected.] The URI value is
whitespace normalized according to the rules for the
<code>xs:anyURI</code> type in <a href="#XMLSchema">[XML
Schema]</a>.</p>
</li>
<li>
<p>[<a name="dt-issd" id="dt-issd" title=
"in-scope schema definitions">Definition</a>: <b>In-scope schema
definitions.</b> This is a generic term for all the element
declarations, attribute declarations, and schema type definitions
that are in scope during processing of an expression.] It includes
the following three parts:</p>
<ul>
<li>
<p>[<a name="dt-is-types" id="dt-is-types" title=
"in-scope schema type">Definition</a>: <b>In-scope schema
types.</b> Each schema type definition is identified either by an
<a title="expanded QName" href="#dt-expanded-qname">expanded
QName</a> (for a <b>named type</b>) or by an <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> type
identifier (for an <b>anonymous type</b>). The in-scope schema
types include the predefined schema types described in <a href=
"#id-predefined-types"><b>2.5.1 Predefined Schema Types</b></a>.
<span class="xquery"><span class="xquery">If the <a title=
"schema import feature" href="#dt-schema-import-feature">Schema
Import Feature</a> is supported, in-scope schema types also include
all type definitions found in imported schemas.</span></span> ]</p>
</li>
<li>
<p>[<a name="dt-is-elems" id="dt-is-elems" title=
"in-scope element declarations">Definition</a>: <b>In-scope element
declarations.</b> Each element declaration is identified either by
an <a title="expanded QName" href="#dt-expanded-qname">expanded
QName</a> (for a top-level element declaration) or by an <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> element
identifier (for a local element declaration). <span class=
"xquery"><span class="xquery">If the <a title=
"schema import feature" href="#dt-schema-import-feature">Schema
Import Feature</a> is supported, in-scope element declarations
include all element declarations found in imported
schemas.</span></span> ] An element declaration includes
information about the element's <a title="substitution group" href=
"#dt-substitution-group">substitution group</a> affiliation.</p>
<p>[<a name="dt-substitution-group" id="dt-substitution-group"
title="substitution group">Definition</a>: <b>Substitution
groups</b> are defined in <a href="#XMLSchema">[XML Schema]</a>
Part 1, Section 2.2.2.2. Informally, the substitution group headed
by a given element (called the <b>head element</b>) consists of the
set of elements that can be substituted for the head element
without affecting the outcome of schema validation.]</p>
</li>
<li>
<p>[<a name="dt-is-attrs" id="dt-is-attrs" title=
"in-scope attribute declarations">Definition</a>: <b>In-scope
attribute declarations.</b> Each attribute declaration is
identified either by an <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (for a top-level attribute
declaration) or by an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
attribute identifier (for a local attribute declaration).
<span class="xquery"><span class="xquery">If the <a title=
"schema import feature" href="#dt-schema-import-feature">Schema
Import Feature</a> is supported, in-scope attribute declarations
include all attribute declarations found in imported
schemas.</span></span>]</p>
</li>
</ul>
</li>
<li>
<p>[<a name="dt-in-scope-variables" id="dt-in-scope-variables"
title="in-scope variables">Definition</a>: <b>In-scope
variables.</b> This is a set of (expanded QName, type) pairs. It
defines the set of variables that are available for reference
within an expression. The <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> is the name of the
variable, and the type is the <a title="static type" href=
"#dt-static-type">static type</a> of the variable.]</p>
<p><span class="xquery"><span class="xquery">Variable declarations
in a <a title="Prolog" href="#dt-prolog">Prolog</a> are added to
<a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a>.</span></span> An
expression that binds a variable (such as a <span class=
"xquery"><span class="xquery"><code>let</code>,</span></span>
<code>for</code>, <code>some</code>, or <code>every</code>
expression) extends the <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> of its
subexpressions with the new bound variable and its type.
<span class="xquery"><span class="xquery">Within a <b>function
declaration</b>, the <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> are extended by the
names and types of the <b>function
parameters</b>.</span></span></p>
<div class="xquery">
<p class="xquery">The static type of a variable may be either
declared in a query or (if the <a title="static typing feature"
href="#dt-static-typing-feature">Static Typing Feature</a> is
enabled) inferred by static type inference rules as described in
<a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal
Semantics (Second Edition)]</a>.</p>
</div>
</li>
<li>
<p>[<a name="dt-context-item-static-type" id=
"dt-context-item-static-type" title=
"context item static type">Definition</a>: <b>Context item static
type.</b> This component defines the <a title="static type" href=
"#dt-static-type">static type</a> of the context item within the
scope of a given expression.]</p>
</li>
<li>
<p>[<a name="dt-function-signature" id="dt-function-signature"
title="function signature">Definition</a>: <b>Function
signatures.</b> This component defines the set of functions that
are available to be called from within an expression. Each function
is uniquely identified by its <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> and its arity (number of
parameters).] In addition to the name and arity, each function
signature specifies the <a title="static type" href=
"#dt-static-type">static types</a> of the function parameters and
result.</p>
<p>The <a title="function signature" href=
"#dt-function-signature">function signatures</a> include the
signatures of <a title="constructor function" href=
"#dt-constructor-function">constructor functions</a>, which are
discussed in <a href="#id-constructor-functions"><b>3.12.5
Constructor Functions</b></a>.</p>
</li>
<li>
<p>[<a name="dt-static-collations" id="dt-static-collations" title=
"statically known collations">Definition</a>: <b>Statically known
collations.</b> This is an <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> set of
(URI, collation) pairs. It defines the names of the collations that
are available for use in processing <span class=
"xquery"><span class="xquery">queries and</span></span>
expressions.] [<a name="dt-collation" id="dt-collation" title=
"collation">Definition</a>: A <b>collation</b> is a specification
of the manner in which strings and URIs are compared and, by
extension, ordered. For a more complete definition of collation,
see <a href="#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0
Functions and Operators (Second Edition)]</a>.]</p>
</li>
<li>
<p>[<a name="dt-def-collation" id="dt-def-collation" title=
"default collation">Definition</a>: <b>Default collation.</b> This
identifies one of the collations in <a title=
"statically known collations" href=
"#dt-static-collations">statically known collations</a> as the
collation to be used by functions and operators for comparing and
ordering values of type <code>xs:string</code> and
<code>xs:anyURI</code> (and types derived from them) when no
explicit collation is specified.]</p>
</li>
<li class="xquery">
<p>[<a name="dt-construction-mode" id="dt-construction-mode" title=
"construction mode">Definition</a>: <b>Construction mode.</b> The
construction mode governs the behavior of element and document node
constructors. If construction mode is <code>preserve</code>, the
type of a constructed element node is <code>xs:anyType</code>, and
all attribute and element nodes copied during node construction
retain their original types. If construction mode is
<code>strip</code>, the type of a constructed element node is
<code>xs:untyped</code>; all element nodes copied during node
construction receive the type <code>xs:untyped</code>, and all
attribute nodes copied during node construction receive the type
<code>xs:untypedAtomic</code>.]</p>
</li>
<li class="xquery">
<p>[<a name="dt-ordering-mode" id="dt-ordering-mode" title=
"ordering mode">Definition</a>: <b>Ordering mode.</b> Ordering
mode, which has the value <code>ordered</code> or
<code>unordered</code>, affects the ordering of the result sequence
returned by certain <a title="path expression" href=
"#dt-path-expression">path expressions</a>, <code>union</code>,
<code>intersect</code>, and <code>except</code> expressions, and
FLWOR expressions that have no <code>order by</code> clause.]
Details are provided in the descriptions of these expressions.</p>
</li>
<li class="xquery">
<p>[<a name="dt-default-empty-order" id="dt-default-empty-order"
title="default order for empty sequences">Definition</a>:
<b>Default order for empty sequences.</b> This component controls
the processing of empty sequences and <code>NaN</code> values as
ordering keys in an <code>order by</code> clause in a FLWOR
expression, as described in <a href="#id-orderby-return"><b>3.8.3
Order By and Return Clauses</b></a>.] Its value may be
<code>greatest</code> or <code>least</code>.</p>
</li>
<li class="xquery">
<p>[<a name="dt-boundary-space-policy" id=
"dt-boundary-space-policy" title=
"boundary-space policy">Definition</a>: <b>Boundary-space
policy.</b> This component controls the processing of <a title=
"boundary whitespace" href="#dt-boundary-whitespace">boundary
whitespace</a> by <a title="direct element constructor" href=
"#dt-direct-elem-const">direct element constructors</a>, as
described in <a href="#id-whitespace"><b>3.7.1.4 Boundary
Whitespace</b></a>.] Its value may be <code>preserve</code> or
<code>strip</code>.</p>
</li>
<li class="xquery">
<p>[<a name="dt-copy-namespaces-mode" id="dt-copy-namespaces-mode"
title="copy-namespaces mode">Definition</a>: <b>Copy-namespaces
mode.</b> This component controls the namespace bindings that are
assigned when an existing element node is copied by an element
constructor, as described in <a href=
"#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a>. Its value consists of two parts:
<code>preserve</code> or <code>no-preserve</code>, and
<code>inherit</code> or <code>no-inherit</code>.]</p>
</li>
<li>
<p>[<a name="dt-base-uri" id="dt-base-uri" title=
"base URI">Definition</a>: <b>Base URI.</b> This is an absolute
URI, used when necessary in the resolution of relative URIs (for
example, by the <code>fn:resolve-uri</code> function.)] The URI
value is whitespace normalized according to the rules for the
<code>xs:anyURI</code> type in <a href="#XMLSchema">[XML
Schema]</a>.</p>
</li>
<li>
<p>[<a name="dt-known-docs" id="dt-known-docs" title=
"statically known documents">Definition</a>: <b>Statically known
documents.</b> This is a mapping from strings onto types. The
string represents the absolute URI of a resource that is
potentially available using the <code>fn:doc</code> function. The
type is the <a title="static type" href="#dt-static-type">static
type</a> of a call to <code>fn:doc</code> with the given URI as its
literal argument. ] If the argument to <code>fn:doc</code> is a
string literal that is not present in <b>statically known
documents</b>, then the <a title="static type" href=
"#dt-static-type">static type</a> of <code>fn:doc</code> is
<code>document-node()?</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The purpose of the <b>statically known documents</b> is to
provide static type information, not to determine which documents
are available. A URI need not be found in the <b>statically known
documents</b> to be accessed using <code>fn:doc</code>.</p>
</div>
</li>
<li>
<p>[<a name="dt-known-collections" id="dt-known-collections" title=
"statically known collections">Definition</a>: <b>Statically known
collections.</b> This is a mapping from strings onto types. The
string represents the absolute URI of a resource that is
potentially available using the <code>fn:collection</code>
function. The type is the type of the sequence of nodes that would
result from calling the <code>fn:collection</code> function with
this URI as its argument.] If the argument to
<code>fn:collection</code> is a string literal that is not present
in <b>statically known collections</b>, then the <a title=
"static type" href="#dt-static-type">static type</a> of
<code>fn:collection</code> is <code>node()*</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The purpose of the <b>statically known collections</b> is to
provide static type information, not to determine which collections
are available. A URI need not be found in the <b>statically known
collections</b> to be accessed using
<code>fn:collection</code>.</p>
</div>
</li>
<li>
<p>[<a name="dt-known-default-collection" id=
"dt-known-default-collection" title=
"statically known default collection type">Definition</a>:
<b>Statically known default collection type.</b> This is the type
of the sequence of nodes that would result from calling the
<code>fn:collection</code> function with no arguments.] Unless
initialized to some other value by an implementation, the value of
<b>statically known default collection type</b> is
<code>node()*</code>.</p>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="eval_context" id="eval_context"></a>2.1.2 Dynamic
Context</h4>
<p>[<a name="dt-dynamic-context" id="dt-dynamic-context" title=
"dynamic context">Definition</a>: The <b>dynamic context</b> of an
expression is defined as information that is available at the time
the expression is evaluated.] If evaluation of an expression relies
on some part of the <a title="dynamic context" href=
"#dt-dynamic-context">dynamic context</a> that has not been
assigned a value, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p>
<p>The individual components of the <a title="dynamic context"
href="#dt-dynamic-context">dynamic context</a> are summarized
below. Further rules governing the semantics of these components
can be found in <a href=
"#id-xq-evaluation-context-components"><b>C.2 Dynamic Context
Components</b></a>.</p>
<p>The <a title="dynamic context" href=
"#dt-dynamic-context">dynamic context</a> consists of all the
components of the <a title="static context" href=
"#dt-static-context">static context</a>, and the additional
components listed below.</p>
<p>[<a name="dt-focus" id="dt-focus" title="focus">Definition</a>:
The first three components of the <a title="dynamic context" href=
"#dt-dynamic-context">dynamic context</a> (context item, context
position, and context size) are called the <b>focus</b> of the
expression. ] The focus enables the processor to keep track of
which items are being processed by the expression.</p>
<p>Certain language constructs, notably the <a title=
"path expression" href="#dt-path-expression">path expression</a>
<code>E1/E2</code> and the <a title="predicate" href=
"#dt-predicate">predicate</a> <code>E1[E2]</code>, create a new
focus for the evaluation of a sub-expression. In these constructs,
<code>E2</code> is evaluated once for each item in the sequence
that results from evaluating <code>E1</code>. Each time
<code>E2</code> is evaluated, it is evaluated with a different
focus. The focus for evaluating <code>E2</code> is referred to
below as the <b>inner focus</b>, while the focus for evaluating
<code>E1</code> is referred to as the <b>outer focus</b>. The inner
focus exists only while <code>E2</code> is being evaluated. When
this evaluation is complete, evaluation of the containing
expression continues with its original focus unchanged.</p>
<ul>
<li>
<p>[<a name="dt-context-item" id="dt-context-item" title=
"context item">Definition</a>: The <b>context item</b> is the item
currently being processed. An item is either an atomic value or a
node.][<a name="dt-context-node" id="dt-context-node" title=
"context node">Definition</a>: When the context item is a node, it
can also be referred to as the <b>context node</b>.] The context
item is returned by an expression consisting of a single dot
(<code>.</code>). When an expression <code>E1/E2</code> or
<code>E1[E2]</code> is evaluated, each item in the sequence
obtained by evaluating <code>E1</code> becomes the context item in
the inner focus for an evaluation of <code>E2</code>.</p>
</li>
<li>
<p>[<a name="dt-context-position" id="dt-context-position" title=
"context position">Definition</a>: The <b>context position</b> is
the position of the context item within the sequence of items
currently being processed.] It changes whenever the context item
changes. When the focus is defined, the value of the context
position is an integer greater than zero. The context position is
returned by the expression <code>fn:position()</code>. When an
expression <code>E1/E2</code> or <code>E1[E2]</code> is evaluated,
the context position in the inner focus for an evaluation of
<code>E2</code> is the position of the context item in the sequence
obtained by evaluating <code>E1</code>. The position of the first
item in a sequence is always 1 (one). The context position is
always less than or equal to the context size.</p>
</li>
<li>
<p>[<a name="dt-context-size" id="dt-context-size" title=
"context size">Definition</a>: The <b>context size</b> is the
number of items in the sequence of items currently being
processed.] Its value is always an integer greater than zero. The
context size is returned by the expression <code>fn:last()</code>.
When an expression <code>E1/E2</code> or <code>E1[E2]</code> is
evaluated, the context size in the inner focus for an evaluation of
<code>E2</code> is the number of items in the sequence obtained by
evaluating <code>E1</code>.</p>
</li>
<li>
<p>[<a name="dt-variable-values" id="dt-variable-values" title=
"variable values">Definition</a>: <b>Variable values</b>. This is a
set of (expanded QName, value) pairs. It contains the same
<a title="expanded QName" href="#dt-expanded-qname">expanded
QNames</a> as the <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> in the <a title=
"static context" href="#dt-static-context">static context</a> for
the expression. The expanded QName is the name of the variable and
the value is the dynamic value of the variable, which includes its
<a title="dynamic type" href="#dt-dynamic-type">dynamic
type</a>.]</p>
</li>
<li>
<p>[<a name="dt-function-implementation" id=
"dt-function-implementation" title=
"function implementation">Definition</a>: <b>Function
implementations</b>. Each function in <a title="function signature"
href="#dt-function-signature">function signatures</a> has a
function implementation that enables the function to map instances
of its parameter types into an instance of its result type.
<span class="xquery"><span class="xquery">For a <a title=
"user-defined function" href="#dt-udf">user-defined function</a>,
the function implementation is an XQuery expression. For a
<a title="built-in function" href="#dt-built-in-function">built-in
function</a> or <a title="external function" href=
"#dt-external-function">external function</a>, the function
implementation is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</span></span>]</p>
</li>
<li>
<p>[<a name="dt-date-time" id="dt-date-time" title=
"current dateTime">Definition</a>: <b>Current dateTime.</b> This
information represents an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> point
in time during the processing of <span class="xquery"><span class=
"xquery">a query</span></span>, and includes an explicit timezone.
It can be retrieved by the <code>fn:current-dateTime</code>
function. If invoked multiple times during the execution of
<span class="xquery"><span class="xquery">a query</span></span>,
this function always returns the same result.]</p>
</li>
<li>
<p>[<a name="dt-timezone" id="dt-timezone" title=
"implicit timezone">Definition</a>: <b>Implicit timezone.</b> This
is the timezone to be used when a date, time, or dateTime value
that does not have a timezone is used in a comparison or arithmetic
operation. The implicit timezone is an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> value of
type <code>xs:dayTimeDuration</code>. See <a href="#XMLSchema">[XML
Schema]</a> for the range of legal values of a timezone.]</p>
</li>
<li>
<p>[<a name="dt-available-docs" id="dt-available-docs" title=
"available documents">Definition</a>: <b>Available documents.</b>
This is a mapping of strings onto document nodes. The string
represents the absolute URI of a resource. The document node is the
root of a tree that represents that resource using the <a title=
"data model" href="#dt-datamodel">data model</a>. The document node
is returned by the <code>fn:doc</code> function when applied to
that URI.] The set of available documents is not limited to the set
of <a title="statically known documents" href=
"#dt-known-docs">statically known documents</a>, and it may be
empty.</p>
<p>If there are one or more URIs in <a title="available documents"
href="#dt-available-docs">available documents</a> that map to a
document node <code>D</code>, then the document-uri property of
<code>D</code> must either be absent, or must be one of these
URIs.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>This means that given a document node <code>$N</code>, the
result of <code>fn:doc(fn:document-uri($N)) is $N</code> will
always be True, unless <code>fn:document-uri($N)</code> is an empty
sequence.</p>
</div>
</li>
<li>
<p>[<a name="dt-available-collections" id=
"dt-available-collections" title=
"available collections">Definition</a>: <b>Available
collections.</b> This is a mapping of strings onto sequences of
nodes. The string represents the absolute URI of a resource. The
sequence of nodes represents the result of the
<code>fn:collection</code> function when that URI is supplied as
the argument. ] The set of available collections is not limited to
the set of <a title="statically known collections" href=
"#dt-known-collections">statically known collections</a>, and it
may be empty.</p>
<p>For every document node <code>D</code> that is in the target of
a mapping in <a title="available collections" href=
"#dt-available-collections">available collections</a>, or that is
the root of a tree containing such a node, the document-uri
property of <code>D</code> must either be absent, or must be a URI
<code>U</code> such that <a title="available documents" href=
"#dt-available-docs">available documents</a> contains a mapping
from <code>U</code> to <code>D</code>."</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>This means that for any document node <code>$N</code> retrieved
using the <code>fn:collection</code> function, either directly or
by navigating to the root of a node that was returned, the result
of <code>fn:doc(fn:document-uri($N)) is $N</code> will always be
True, unless <code>fn:document-uri($N)</code> is an empty sequence.
This implies a requirement for the <code>fn:doc</code> and
<code>fn:collection</code> functions to be consistent in their
effect. If the implementation uses catalogs or user-supplied URI
resolvers to dereference URIs supplied to the <code>fn:doc</code>
function, the implementation of the <code>fn:collection</code>
function must take these mechanisms into account. For example, an
implementation might achieve this by mapping the collection URI to
a set of document URIs, which are then resolved using the same
catalog or URI resolver that is used by the <code>fn:doc</code>
function.</p>
</div>
</li>
<li>
<p>[<a name="dt-default-collection" id="dt-default-collection"
title="default collection">Definition</a>: <b>Default
collection.</b> This is the sequence of nodes that would result
from calling the <code>fn:collection</code> function with no
arguments.] The value of <b>default collection</b> may be
initialized by the implementation.</p>
</li>
</ul>
</div>
</div>
<div class="div2">
<h3><a name="id-processing-model" id="id-processing-model"></a>2.2
Processing Model</h3>
<p>XQuery is defined in terms of the <a title="data model" href=
"#dt-datamodel">data model</a> and the <a title=
"expression context" href="#dt-expression-context">expression
context</a>.</p>
<img src="ProcMod-XQuery.gif" alt="Processing Model Overview" />
<p>Figure 1: Processing Model Overview</p>
<p>Figure 1 provides a schematic overview of the processing steps
that are discussed in detail below. Some of these steps are
completely outside the domain of XQuery; in Figure 1, these are
depicted outside the line that represents the boundaries of the
language, an area labeled <b>external processing</b>. The external
processing domain includes generation of an <a title="XDM instance"
href="#dt-data-model-instance">XDM instance</a> that represents the
data to be queried (see <a href=
"#id-data-model-generation"><b>2.2.1 Data Model
Generation</b></a>), schema import processing (see <a href=
"#id-schema-import-processing"><b>2.2.2 Schema Import
Processing</b></a>) and serialization (see <a href=
"#id-serialization"><b>2.2.4 Serialization</b></a>). The area
inside the boundaries of the language is known as the <span class=
"xquery"><span class="xquery"><b>query processing
domain</b></span></span>, which includes the static analysis and
dynamic evaluation phases (see <a href=
"#id-expression-processing"><b>2.2.3 Expression
Processing</b></a>). Consistency constraints on the <span class=
"xquery"><span class="xquery">query</span></span> processing domain
are defined in <a href="#id-consistency-constraints"><b>2.2.5
Consistency Constraints</b></a>.</p>
<div class="div3">
<h4><a name="id-data-model-generation" id=
"id-data-model-generation"></a>2.2.1 Data Model Generation</h4>
<p>Before <span class="xquery"><span class="xquery">a
query</span></span> can be processed, its input data must be
represented as an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a>. This process occurs
outside the domain of XQuery, which is why Figure 1 represents it
in the external processing domain. Here are some steps by which an
XML document might be converted to an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a>:</p>
<ol class="enumar">
<li>
<p>A document may be parsed using an XML parser that generates an
<b>XML Information Set</b> (see <a href="#XINFO">[XML
Infoset]</a>). The parsed document may then be validated against
one or more schemas. This process, which is described in <a href=
"#XMLSchema">[XML Schema]</a>, results in an abstract information
structure called the <b>Post-Schema Validation Infoset</b> (PSVI).
If a document has no associated schema, its Information Set is
preserved. (See DM1 in Fig. 1.)</p>
</li>
<li>
<p>The Information Set or PSVI may be transformed into an <a title=
"XDM instance" href="#dt-data-model-instance">XDM instance</a> by a
process described in <a href="#datamodel">[XQuery 1.0 and XPath 2.0
Data Model (Second Edition)]</a>. (See DM2 in Fig. 1.)</p>
</li>
</ol>
<p>The above steps provide an example of how an <a title=
"XDM instance" href="#dt-data-model-instance">XDM instance</a>
might be constructed. An XDM instance might also be synthesized
directly from a relational database, or constructed in some other
way (see DM3 in Fig. 1.) XQuery is defined in terms of the
<a title="data model" href="#dt-datamodel">data model</a>, but it
does not place any constraints on how XDM instances are
constructed.</p>
<p>[<a name="dt-type-annotation" id="dt-type-annotation" title=
"type annotation">Definition</a>: Each element node and attribute
node in an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a> has a <b>type
annotation</b> (referred to in <a href="#datamodel">[XQuery 1.0 and
XPath 2.0 Data Model (Second Edition)]</a> as its
<code>type-name</code> property.) The type annotation of a node is
a <a title="schema type" href="#dt-schema-type">schema type</a>
that describes the relationship between the <a title="string value"
href="#dt-string-value">string value</a> of the node and its
<a title="typed value" href="#dt-typed-value">typed value</a>.] If
the <a title="XDM instance" href="#dt-data-model-instance">XDM
instance</a> was derived from a validated XML document as described
in <a href=
"http://www.w3.org/TR/xpath-datamodel/#const-psvi">Section 3.3
Construction from a PSVI</a><sup><small>DM</small></sup>, the type
annotations of the element and attribute nodes are derived from
schema validation. XQuery does not provide a way to directly access
the type annotation of an element or attribute node.</p>
<p>The value of an attribute is represented directly within the
attribute node. An attribute node whose type is unknown (such as
might occur in a schemaless document) is given the <a title=
"type annotation" href="#dt-type-annotation">type annotation</a>
<code>xs:untypedAtomic</code>.</p>
<p>The value of an element is represented by the children of the
element node, which may include text nodes and other element nodes.
The <a title="type annotation" href="#dt-type-annotation">type
annotation</a> of an element node indicates how the values in its
child text nodes are to be interpreted. An element that has not
been validated (such as might occur in a schemaless document) is
annotated with the schema type <code>xs:untyped</code>. An element
that has been validated and found to be partially valid is
annotated with the schema type <code>xs:anyType</code>. If an
element node is annotated as <code>xs:untyped</code>, all its
descendant element nodes are also annotated as
<code>xs:untyped</code>. However, if an element node is annotated
as <code>xs:anyType</code>, some of its descendant element nodes
may have a more specific <a title="type annotation" href=
"#dt-type-annotation">type annotation</a>.</p>
</div>
<div class="div3">
<h4><a name="id-schema-import-processing" id=
"id-schema-import-processing"></a>2.2.2 Schema Import
Processing</h4>
<div class="xquery">
<p class="xquery">The <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a> in the <a title=
"static context" href="#dt-static-context">static context</a> may
be extracted from actual XML schemas as described in <a href=
"#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal Semantics
(Second Edition)]</a> (see step SI1 in Figure 1) or may be
generated by some other mechanism (see step SI2 in Figure 1). In
either case, the result must satisfy the consistency constraints
defined in <a href="#id-consistency-constraints"><b>2.2.5
Consistency Constraints</b></a>.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-expression-processing" id=
"id-expression-processing"></a>2.2.3 Expression Processing</h4>
<p>XQuery defines two phases of processing called the <a title=
"static analysis phase" href="#dt-static-analysis">static analysis
phase</a> and the <a title="dynamic evaluation phase" href=
"#dt-dynamic-evaluation">dynamic evaluation phase</a> (see Fig. 1).
During the static analysis phase, <a title="static error" href=
"#dt-static-error">static errors</a>, <a title="dynamic error"
href="#dt-dynamic-error">dynamic errors</a>, or <a title=
"type error" href="#dt-type-error">type errors</a> may be raised.
During the dynamic evaluation phase, only <a title="dynamic error"
href="#dt-dynamic-error">dynamic errors</a> or <a title=
"type error" href="#dt-type-error">type errors</a> may be raised.
These kinds of errors are defined in <a href=
"#id-kinds-of-errors"><b>2.3.1 Kinds of Errors</b></a>.</p>
<p>Within each phase, an implementation is free to use any strategy
or algorithm whose result conforms to the specifications in this
document.</p>
<div class="div4">
<h5><a name="id-static-analysis" id=
"id-static-analysis"></a>2.2.3.1 Static Analysis Phase</h5>
<p>[<a name="dt-static-analysis" id="dt-static-analysis" title=
"static analysis phase">Definition</a>: The <b>static analysis
phase</b> depends on the expression itself and on the <a title=
"static context" href="#dt-static-context">static context</a>. The
<b>static analysis phase</b> does not depend on input data (other
than schemas).]</p>
<p>During the static analysis phase, the <span class=
"xquery"><span class="xquery">query</span></span> is parsed into an
internal representation called the <b>operation tree</b> (step SQ1
in Figure 1). A parse error is raised as a <a title="static error"
href="#dt-static-error">static error</a> [<a href="#ERRXPST0003"
title="err:XPST0003">err:XPST0003</a>]. The <a title=
"static context" href="#dt-static-context">static context</a> is
initialized by the implementation (step SQ2). <span class=
"xquery"><span class="xquery">The <a title="static context" href=
"#dt-static-context">static context</a> is then changed and
augmented based on information in the <b>prolog</b> (step SQ3). If
the <a title="schema import feature" href=
"#dt-schema-import-feature">Schema Import Feature</a> is supported,
the <a title="in-scope schema definitions" href="#dt-issd">in-scope
schema definitions</a> are populated with information from imported
schemas. If the <a title="module feature" href=
"#dt-module-feature">Module Feature</a> is supported, the static
context is extended with function declarations and variable
declarations from imported modules.</span></span> The <a title=
"static context" href="#dt-static-context">static context</a> is
used to resolve schema type names, function names, namespace
prefixes, and variable names (step SQ4). If a name of one of these
kinds in the <b>operation tree</b> is not found in the <a title=
"static context" href="#dt-static-context">static context</a>, a
<a title="static error" href="#dt-static-error">static error</a>
([<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] or
[<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]) is
raised (however, see exceptions to this rule in <a href=
"#id-element-test"><b>2.5.4.3 Element Test</b></a> and <a href=
"#id-attribute-test"><b>2.5.4.5 Attribute Test</b></a>.)</p>
<p>The <b>operation tree</b> is then <b>normalized</b> by making
explicit the implicit operations such as <a title="atomization"
href="#dt-atomization">atomization</a> and extraction of <a title=
"effective boolean value" href="#dt-ebv">Effective Boolean
Values</a> (step SQ5). The normalization process is described in
<a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal
Semantics (Second Edition)]</a>.</p>
<p>Each expression is then assigned a <a title="static type" href=
"#dt-static-type">static type</a> (step SQ6). [<a name=
"dt-static-type" id="dt-static-type" title=
"static type">Definition</a>: The <b>static type</b> of an
expression is a type such that, when the expression is evaluated,
the resulting value will always conform to the static type.] If the
<a title="static typing feature" href=
"#dt-static-typing-feature">Static Typing Feature</a> is supported,
the <a title="static type" href="#dt-static-type">static types</a>
of various expressions are inferred according to the rules
described in <a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath
2.0 Formal Semantics (Second Edition)]</a>. If the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is not supported, the static types that are
assigned are <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
<p>During the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>, if the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is in effect and an operand of an expression is
found to have a <a title="static type" href=
"#dt-static-type">static type</a> that is not appropriate for that
operand, a <a title="type error" href="#dt-type-error">type
error</a> is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>]. If static type checking raises no
errors and assigns a <a title="static type" href=
"#dt-static-type">static type</a> T to an expression, then
execution of the expression on valid input data is guaranteed
either to produce a value of type T or to raise a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a>.</p>
<p>The purpose of the <a title="static typing feature" href=
"#dt-static-typing-feature">Static Typing Feature</a> is to provide
early detection of <a title="type error" href="#dt-type-error">type
errors</a> and to infer type information that may be useful in
optimizing the evaluation of an expression.</p>
</div>
<div class="div4">
<h5><a name="id-dynamic-evaluation" id=
"id-dynamic-evaluation"></a>2.2.3.2 Dynamic Evaluation Phase</h5>
<p>[<a name="dt-dynamic-evaluation" id="dt-dynamic-evaluation"
title="dynamic evaluation phase">Definition</a>: The <b>dynamic
evaluation phase</b> is the phase during which the value of an
expression is computed.] It occurs after completion of the
<a title="static analysis phase" href="#dt-static-analysis">static
analysis phase</a>.</p>
<p>The dynamic evaluation phase can occur only if no errors were
detected during the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>. If the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is in effect, all <a title="type error" href=
"#dt-type-error">type errors</a> are detected during static
analysis and serve to inhibit the dynamic evaluation phase.</p>
<p>The dynamic evaluation phase depends on the <b>operation
tree</b> of the expression being evaluated (step DQ1), on the input
data (step DQ4), and on the <a title="dynamic context" href=
"#dt-dynamic-context">dynamic context</a> (step DQ5), which in turn
draws information from the external environment (step DQ3) and the
<a title="static context" href="#dt-static-context">static
context</a> (step DQ2). The dynamic evaluation phase may create new
data-model values (step DQ4) and it may extend the <a title=
"dynamic context" href="#dt-dynamic-context">dynamic context</a>
(step DQ5)—for example, by binding values to variables.</p>
<p>[<a name="dt-dynamic-type" id="dt-dynamic-type" title=
"dynamic type">Definition</a>: A <b>dynamic type</b> is associated
with each value as it is computed. The dynamic type of a value may
be more specific than the <a title="static type" href=
"#dt-static-type">static type</a> of the expression that computed
it (for example, the static type of an expression might be
<code>xs:integer*</code>, denoting a sequence of zero or more
integers, but at evaluation time its value may have the dynamic
type <code>xs:integer</code>, denoting exactly one integer.)]</p>
<p>If an operand of an expression is found to have a <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a> that is not
appropriate for that operand, a <a title="type error" href=
"#dt-type-error">type error</a> is raised [<a href="#ERRXPTY0004"
title="err:XPTY0004">err:XPTY0004</a>].</p>
<p>Even though static typing can catch many <a title="type error"
href="#dt-type-error">type errors</a> before an expression is
executed, it is possible for an expression to raise an error during
evaluation that was not detected by static analysis. For example,
an expression may contain a cast of a string into an integer, which
is statically valid. However, if the actual value of the string at
run time cannot be cast into an integer, a <a title="dynamic error"
href="#dt-dynamic-error">dynamic error</a> will result. Similarly,
an expression may apply an arithmetic operator to a value whose
<a title="static type" href="#dt-static-type">static type</a> is
<code>xs:untypedAtomic</code>. This is not a <a title=
"static error" href="#dt-static-error">static error</a>, but at run
time, if the value cannot be successfully cast to a <a title=
"numeric" href="#dt-numeric">numeric</a> type, a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a> will be
raised.</p>
<p>When the <a title="static typing feature" href=
"#dt-static-typing-feature">Static Typing Feature</a> is in effect,
it is also possible for static analysis of an expression to raise a
<a title="type error" href="#dt-type-error">type error</a>, even
though execution of the expression on certain inputs would be
successful. For example, an expression might contain a function
that requires an element as its parameter, and the static analysis
phase might infer the <a title="static type" href=
"#dt-static-type">static type</a> of the function parameter to be
an optional element. This case is treated as a <a title=
"type error" href="#dt-type-error">type error</a> and inhibits
evaluation, even though the function call would have been
successful for input data in which the optional element is
present.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-serialization" id="id-serialization"></a>2.2.4
Serialization</h4>
<p>[<a name="dt-serialization" id="dt-serialization" title=
"serialization">Definition</a>: <b>Serialization</b> is the process
of converting an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a> into a sequence of
octets (step DM4 in Figure 1.) ] The general framework for
serialization is described in <a href="#serialization">[XSLT 2.0
and XQuery 1.0 Serialization (Second Edition)]</a>.</p>
<div class="xquery">
<p class="xquery">An XQuery implementation is not required to
provide a serialization interface. For example, an implementation
may only provide a DOM interface (see <a href="#DOM">[Document
Object Model]</a>) or an interface based on an event stream. In
these cases, serialization would be outside of the scope of this
specification.</p>
</div>
<div class="xquery">
<p class="xquery"><a href="#serialization">[XSLT 2.0 and XQuery 1.0
Serialization (Second Edition)]</a> defines a set of
<b>serialization parameters</b> that govern the serialization
process. If an XQuery implementation provides a serialization
interface, it may support (and may expose to users) any of the
serialization parameters listed (with default values) in <a href=
"#id-xq-serialization-parameters"><b>C.3 Serialization
Parameters</b></a>. An XQuery implementation that provides a
serialization interface must support some combination of
serialization parameters in which <code>method = "xml"</code> and
<code>version = "1.0"</code>.</p>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The <a title="data model" href="#dt-datamodel">data model</a>
permits an element node to have fewer <a title=
"in-scope namespaces" href="#dt-in-scope-namespaces">in-scope
namespaces</a> than its parent. Correct serialization of such an
element node would require "undeclaration" of namespaces, which is
a feature of <a href="#XMLNAMES11">[XML Names 1.1]</a>. An
implementation that does not support <a href="#XMLNAMES11">[XML
Names 1.1]</a> is permitted to serialize such an element without
"undeclaration" of namespaces, which effectively causes the element
to inherit the in-scope namespaces of its parent.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-consistency-constraints" id=
"id-consistency-constraints"></a>2.2.5 Consistency Constraints</h4>
<p>In order for XQuery to be well defined, the input <a title=
"XDM instance" href="#dt-data-model-instance">XDM instance</a>, the
<a title="static context" href="#dt-static-context">static
context</a>, and the <a title="dynamic context" href=
"#dt-dynamic-context">dynamic context</a> must be mutually
consistent. The consistency constraints listed below are
prerequisites for correct functioning of an XQuery implementation.
Enforcement of these consistency constraints is beyond the scope of
this specification. This specification does not define the result
of <span class="xquery"><span class="xquery">a query</span></span>
under any condition in which one or more of these constraints is
not satisfied.</p>
<p>Some of the consistency constraints use the term <b>data model
schema</b>. [<a name="dt-data-model-schema" id=
"dt-data-model-schema" title="data model schema">Definition</a>:
For a given node in an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a>, the <b>data model
schema</b> is defined as the schema from which the <a title=
"type annotation" href="#dt-type-annotation">type annotation</a> of
that node was derived.] For a node that was constructed by some
process other than schema validation, the <b>data model schema</b>
consists simply of the schema type definition that is represented
by the <a title="type annotation" href="#dt-type-annotation">type
annotation</a> of the node.</p>
<ul>
<li>
<p>For every node that has a type annotation, if that type
annotation is found in the <a title="in-scope schema definitions"
href="#dt-issd">in-scope schema definitions</a> (ISSD), then its
definition in the ISSD must be equivalent to its definition in the
<a title="data model schema" href="#dt-data-model-schema">data
model schema</a>. Furthermore, all types that are derived by
extension from the given type in the <a title="data model schema"
href="#dt-data-model-schema">data model schema</a> must also be
known by equivalent definitions in the ISSD.</p>
</li>
<li>
<p>For every element name <em>EN</em> that is found both in an
<a title="XDM instance" href="#dt-data-model-instance">XDM
instance</a> and in the <a title="in-scope schema definitions"
href="#dt-issd">in-scope schema definitions</a> (ISSD), all
elements that are known in the <a title="data model schema" href=
"#dt-data-model-schema">data model schema</a> to be in the
<a title="substitution group" href=
"#dt-substitution-group">substitution group</a> headed by
<em>EN</em> must also be known in the ISSD to be in the <a title=
"substitution group" href="#dt-substitution-group">substitution
group</a> headed by <em>EN</em>.</p>
</li>
<li>
<p>Every element name, attribute name, or schema type name
referenced in <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> or <a title=
"function signature" href="#dt-function-signature">function
signatures</a> must be in the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a>, unless it is an element name referenced as part of
an <a href="#doc-xquery-ElementTest">ElementTest</a> or an
attribute name referenced as part of an <a href=
"#doc-xquery-AttributeTest">AttributeTest</a>.</p>
</li>
<li>
<p>Any reference to a global element, attribute, or type name in
the <a title="in-scope schema definitions" href="#dt-issd">in-scope
schema definitions</a> must have a corresponding element, attribute
or type definition in the <a title="in-scope schema definitions"
href="#dt-issd">in-scope schema definitions</a>.</p>
</li>
<li>
<p>For each mapping of a string to a document node in <a title=
"available documents" href="#dt-available-docs">available
documents</a>, if there exists a mapping of the same string to a
document type in <a title="statically known documents" href=
"#dt-known-docs">statically known documents</a>, the document node
must match the document type, using the matching rules in <a href=
"#id-sequencetype-matching"><b>2.5.4 SequenceType
Matching</b></a>.</p>
</li>
<li>
<p>For each mapping of a string to a sequence of nodes in <a title=
"available collections" href="#dt-available-collections">available
collections</a>, if there exists a mapping of the same string to a
type in <a title="statically known collections" href=
"#dt-known-collections">statically known collections</a>, the
sequence of nodes must match the type, using the matching rules in
<a href="#id-sequencetype-matching"><b>2.5.4 SequenceType
Matching</b></a>.</p>
</li>
<li>
<p>The sequence of nodes in the <a title="default collection" href=
"#dt-default-collection">default collection</a> must match the
<a title="statically known default collection type" href=
"#dt-known-default-collection">statically known default collection
type</a>, using the matching rules in <a href=
"#id-sequencetype-matching"><b>2.5.4 SequenceType
Matching</b></a>.</p>
</li>
<li>
<p>The value of the <a title="context item" href=
"#dt-context-item">context item</a> must match the <a title=
"context item static type" href=
"#dt-context-item-static-type">context item static type</a>, using
the matching rules in <a href="#id-sequencetype-matching"><b>2.5.4
SequenceType Matching</b></a>.</p>
</li>
<li>
<p>For each (variable, type) pair in <a title="in-scope variables"
href="#dt-in-scope-variables">in-scope variables</a> and the
corresponding (variable, value) pair in <a title="variable values"
href="#dt-variable-values">variable values</a> such that the
variable names are equal, the value must match the type, using the
matching rules in <a href="#id-sequencetype-matching"><b>2.5.4
SequenceType Matching</b></a>.</p>
</li>
<li class="xquery">
<p>For each variable declared as <code>external</code>: If the
variable declaration includes a declared type, the external
environment must provide a value for the variable that matches the
declared type, using the matching rules in <a href=
"#id-sequencetype-matching"><b>2.5.4 SequenceType Matching</b></a>.
If the variable declaration does not include a declared type, the
external environment must provide a type and a matching value,
using the same matching rules.</p>
</li>
<li class="xquery">
<p>For each function declared as external: the <a title=
"function implementation" href=
"#dt-function-implementation">function implementation</a> must
either return a value that matches the declared result type, using
the matching rules in <a href="#id-sequencetype-matching"><b>2.5.4
SequenceType Matching</b></a>, or raise an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> error.</p>
</li>
<li class="xquery">
<p>For a given query, define a <b>participating ISSD</b> as the
<a title="in-scope schema definitions" href="#dt-issd">in-scope
schema definitions</a> of a module that is used in evaluating the
query. If two participating ISSDs contain a definition for the same
schema type, element name, or attribute name, the definitions must
be equivalent in both ISSDs. Furthermore, if two participating
ISSDs each contain a definition of a schema type <em>T</em>, the
set of types derived by extension from <em>T</em> must be
equivalent in both ISSDs. Also, if two participating ISSDs each
contain a definition of an element name <em>E</em>, the
substitution group headed by <em>E</em> must be equivalent in both
ISSDs.</p>
</li>
<li>
<p>In the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>, the prefix
<code>xml</code> must not be bound to any namespace URI other than
<code>http://www.w3.org/XML/1998/namespace</code>, and no prefix
other than <code>xml</code> may be bound to this namespace URI.</p>
</li>
</ul>
</div>
</div>
<div class="div2">
<h3><a name="errors" id="errors"></a>2.3 Error Handling</h3>
<div class="div3">
<h4><a name="id-kinds-of-errors" id="id-kinds-of-errors"></a>2.3.1
Kinds of Errors</h4>
<p>As described in <a href="#id-expression-processing"><b>2.2.3
Expression Processing</b></a>, XQuery defines a <a title=
"static analysis phase" href="#dt-static-analysis">static analysis
phase</a>, which does not depend on input data, and a <a title=
"dynamic evaluation phase" href="#dt-dynamic-evaluation">dynamic
evaluation phase</a>, which does depend on input data. Errors may
be raised during each phase.</p>
<p>[<a name="dt-static-error" id="dt-static-error" title=
"static error">Definition</a>: A <b>static error</b> is an error
that must be detected during the static analysis phase. A syntax
error is an example of a <a title="static error" href=
"#dt-static-error">static error</a>.]</p>
<p>[<a name="dt-dynamic-error" id="dt-dynamic-error" title=
"dynamic error">Definition</a>: A <b>dynamic error</b> is an error
that must be detected during the dynamic evaluation phase and may
be detected during the static analysis phase. Numeric overflow is
an example of a dynamic error. ]</p>
<p>[<a name="dt-type-error" id="dt-type-error" title=
"type error">Definition</a>: A <b>type error</b> may be raised
during the static analysis phase or the dynamic evaluation phase.
During the static analysis phase, a <a title="type error" href=
"#dt-type-error">type error</a> occurs when the <a title=
"static type" href="#dt-static-type">static type</a> of an
expression does not match the expected type of the context in which
the expression occurs. During the dynamic evaluation phase, a
<a title="type error" href="#dt-type-error">type error</a> occurs
when the <a title="dynamic type" href="#dt-dynamic-type">dynamic
type</a> of a value does not match the expected type of the context
in which the value occurs.]</p>
<p>The outcome of the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a> is either success
or one or more <a title="type error" href="#dt-type-error">type
errors</a>, <a title="static error" href="#dt-static-error">static
errors</a>, or statically-detected <a title="dynamic error" href=
"#dt-dynamic-error">dynamic errors</a>. The result of the <a title=
"dynamic evaluation phase" href="#dt-dynamic-evaluation">dynamic
evaluation phase</a> is either a result value, a <a title=
"type error" href="#dt-type-error">type error</a>, or a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a>.</p>
<p>If more than one error is present, or if an error condition
comes within the scope of more than one error defined in this
specification, then any non-empty subset of these errors may be
reported.</p>
<p>During the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>, if the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is in effect and the <a title="static type"
href="#dt-static-type">static type</a> assigned to an expression
other than <code>()</code> or <code>data(())</code> is
<code>empty-sequence()</code>, a <a title="static error" href=
"#dt-static-error">static error</a> is raised [<a href=
"#ERRXPST0005" title="err:XPST0005">err:XPST0005</a>]. This catches
cases in which a query refers to an element or attribute that is
not present in the <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a>, possibly because of a
spelling error.</p>
<p>Independently of whether the <a title="static typing feature"
href="#dt-static-typing-feature">Static Typing Feature</a> is in
effect, if an implementation can determine during the <a title=
"static analysis phase" href="#dt-static-analysis">static analysis
phase</a> that an expression, if evaluated, would necessarily raise
a <a title="type error" href="#dt-type-error">type error</a> or a
<a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a>, the implementation may (but is not required to) report
that error during the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>. However, the
<code>fn:error()</code> function must not be evaluated during the
<a title="static analysis phase" href="#dt-static-analysis">static
analysis phase</a>.</p>
<p>[<a name="dt-warning" id="dt-warning" title=
"warning">Definition</a>: In addition to <a title="static error"
href="#dt-static-error">static errors</a>, <a title="dynamic error"
href="#dt-dynamic-error">dynamic errors</a>, and <a title=
"type error" href="#dt-type-error">type errors</a>, an XQuery
implementation may raise <b>warnings</b>, either during the
<a title="static analysis phase" href="#dt-static-analysis">static
analysis phase</a> or the <a title="dynamic evaluation phase" href=
"#dt-dynamic-evaluation">dynamic evaluation phase</a>. The
circumstances in which warnings are raised, and the ways in which
warnings are handled, are <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.]</p>
<p>In addition to the errors defined in this specification, an
implementation may raise a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> for a reason beyond the scope
of this specification. For example, limitations may exist on the
maximum numbers or sizes of various objects. Any such limitations,
and the consequences of exceeding them, are <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
</div>
<div class="div3">
<h4><a name="id-identifying-errors" id=
"id-identifying-errors"></a>2.3.2 Identifying and Reporting
Errors</h4>
<p>The errors defined in this specification are identified by
QNames that have the form <code>err:XXYYnnnn</code>, where:</p>
<ul>
<li>
<p><code>err</code> denotes the namespace for XPath and XQuery
errors, <code>http://www.w3.org/2005/xqt-errors</code>. This
binding of the namespace prefix <code>err</code> is used for
convenience in this document, and is not normative.</p>
</li>
<li class="xquery">
<p><code>XX</code> denotes the language in which the error is
defined, using the following encoding:</p>
<ul>
<li>
<p><code>XP</code> denotes an error defined by XPath. Such an error
may also occur XQuery since XQuery includes XPath as a subset.</p>
</li>
<li>
<p><code>XQ</code> denotes an error defined by XQuery.</p>
</li>
</ul>
</li>
<li>
<p><code>YY</code> denotes the error category, using the following
encoding:</p>
<ul>
<li>
<p><code>ST</code> denotes a static error.</p>
</li>
<li>
<p><code>DY</code> denotes a dynamic error.</p>
</li>
<li>
<p><code>TY</code> denotes a type error.</p>
</li>
</ul>
</li>
<li>
<p><code>nnnn</code> is a unique numeric code.</p>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The namespace URI for XPath and XQuery errors is not expected to
change from one version of XQuery to another. However, the contents
of this namespace may be extended to include additional error
definitions.</p>
</div>
<p>The method by which an XQuery processor reports error
information to the external environment is <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
<p>An error can be represented by a URI reference that is derived
from the error QName as follows: an error with namespace URI
<em><code>NS</code></em> and local part <em><code>LP</code></em>
can be represented as the URI reference
<em><code>NS</code></em><code>#</code><em><code>LP</code></em>. For
example, an error whose QName is <code>err:XPST0017</code> could be
represented as
<code>http://www.w3.org/2005/xqt-errors#XPST0017</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Along with a code identifying an error, implementations may wish
to return additional information, such as the location of the error
or the processing phase in which it was detected. If an
implementation chooses to do so, then the mechanism that it uses to
return this information is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-handling-dynamic" id=
"id-handling-dynamic"></a>2.3.3 Handling Dynamic Errors</h4>
<p>Except as noted in this document, if any operand of an
expression raises a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a>, the expression also raises a
<a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a>. If an expression can validly return a value or raise a
dynamic error, the implementation may choose to return the value or
raise the dynamic error. For example, the logical expression
<code>expr1 and expr2</code> may return the value
<code>false</code> if either operand returns <code>false</code>, or
may raise a dynamic error if either operand raises a dynamic
error.</p>
<p>If more than one operand of an expression raises an error, the
implementation may choose which error is raised by the expression.
For example, in this expression:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
($x div $y) + xs:decimal($z)
</pre></div>
</div>
<p>both the sub-expressions <code>($x div $y)</code> and
<code>xs:decimal($z)</code> may raise an error. The implementation
may choose which error is raised by the "<code>+</code>"
expression. Once one operand raises an error, the implementation is
not required, but is permitted, to evaluate any other operands.</p>
<p>[<a name="dt-error-value" id="dt-error-value" title=
"error value">Definition</a>: In addition to its identifying QName,
a dynamic error may also carry a descriptive string and one or more
additional values called <b>error values</b>.] An implementation
may provide a mechanism whereby an application-defined error
handler can process error values and produce diagnostic
messages.</p>
<p>A dynamic error may be raised by a <a title="built-in function"
href="#dt-built-in-function">built-in function</a> or operator. For
example, the <code>div</code> operator raises an error if its
operands are <code>xs:decimal</code> values and its second operand
is equal to zero. Errors raised by built-in functions and operators
are defined in <a href="#FunctionsAndOperators">[XQuery 1.0 and
XPath 2.0 Functions and Operators (Second Edition)]</a>.</p>
<p>A dynamic error can also be raised explicitly by calling the
<code>fn:error</code> function, which only raises an error and
never returns a value. This function is defined in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>. For example, the following
function call raises a dynamic error, providing a QName that
identifies the error, a descriptive string, and a diagnostic value
(assuming that the prefix <code>app</code> is bound to a namespace
containing application-defined error codes):</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
fn:error(xs:QName("app:err057"), "Unexpected value", fn:string($v))
</pre></div>
</div>
</div>
<div class="div3">
<h4><a name="id-errors-and-opt" id="id-errors-and-opt"></a>2.3.4
Errors and Optimization</h4>
<p>Because different implementations may choose to evaluate or
optimize an expression in different ways, certain aspects of the
detection and reporting of <a title="dynamic error" href=
"#dt-dynamic-error">dynamic errors</a> are <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>, as
described in this section.</p>
<p>An implementation is always free to evaluate the operands of an
operator in any order.</p>
<p>In some cases, a processor can determine the result of an
expression without accessing all the data that would be implied by
the formal expression semantics. For example, the formal
description of <a title="filter expression" href=
"#dt-filter-expression">filter expressions</a> suggests that
<code>$s[1]</code> should be evaluated by examining all the items
in sequence <code>$s</code>, and selecting all those that satisfy
the predicate <code>position()=1</code>. In practice, many
implementations will recognize that they can evaluate this
expression by taking the first item in the sequence and then
exiting. If <code>$s</code> is defined by an expression such as
<code>//book[author eq 'Berners-Lee']</code>, then this strategy
may avoid a complete scan of a large document and may therefore
greatly improve performance. However, a consequence of this
strategy is that a dynamic error or type error that would be
detected if the expression semantics were followed literally might
not be detected at all if the evaluation exits early. In this
example, such an error might occur if there is a <code>book</code>
element in the input data with more than one <code>author</code>
subelement.</p>
<p>The extent to which a processor may optimize its access to data,
at the cost of not detecting errors, is defined by the following
rules.</p>
<p>Consider an expression <em>Q</em> that has an operand
(sub-expression) <em>E</em>. In general the value of <em>E</em> is
a sequence. At an intermediate stage during evaluation of the
sequence, some of its items will be known and others will be
unknown. If, at such an intermediate stage of evaluation, a
processor is able to establish that there are only two possible
outcomes of evaluating <em>Q</em>, namely the value <em>V</em> or
an error, then the processor may deliver the result <em>V</em>
without evaluating further items in the operand <em>E</em>. For
this purpose, two values are considered to represent the same
outcome if their items are pairwise the same, where nodes are the
same if they have the same identity, and values are the same if
they are equal and have exactly the same type.</p>
<p>There is an exception to this rule: If a processor evaluates an
operand <em>E</em> (wholly or in part), then it is required to
establish that the actual value of the operand <em>E</em> does not
violate any constraints on its cardinality. For example, the
expression <code>$e eq 0</code> results in a type error if the
value of <code>$e</code> contains two or more items. A processor is
not allowed to decide, after evaluating the first item in the value
of <code>$e</code> and finding it equal to zero, that the only
possible outcomes are the value <code>true</code> or a type error
caused by the cardinality violation. It must establish that the
value of <code>$e</code> contains no more than one item.</p>
<p>These rules apply to all the operands of an expression
considered in combination: thus if an expression has two operands
<em>E1</em> and <em>E2</em>, it may be evaluated using any samples
of the respective sequences that satisfy the above rules.</p>
<p>The rules cascade: if <em>A</em> is an operand of <em>B</em> and
<em>B</em> is an operand of <em>C</em>, then the processor needs to
evaluate only a sufficient sample of <em>B</em> to determine the
value of <em>C</em>, and needs to evaluate only a sufficient sample
of <em>A</em> to determine this sample of <em>B</em>.</p>
<p>The effect of these rules is that the processor is free to stop
examining further items in a sequence as soon as it can establish
that further items would not affect the result except possibly by
causing an error. For example, the processor may return
<code>true</code> as the result of the expression <code>S1 =
S2</code> as soon as it finds a pair of equal values from the two
sequences.</p>
<p>Another consequence of these rules is that where none of the
items in a sequence contributes to the result of an expression, the
processor is not obliged to evaluate any part of the sequence.
Again, however, the processor cannot dispense with a required
cardinality check: if an empty sequence is not permitted in the
relevant context, then the processor must ensure that the operand
is not an empty sequence.</p>
<p>Examples:</p>
<ul>
<li>
<p>If an implementation can find (for example, by using an index)
that at least one item returned by <code>$expr1</code> in the
following example has the value <code>47</code>, it is allowed to
return <code>true</code> as the result of the <code>some</code>
expression, without searching for another item returned by
<code>$expr1</code> that would raise an error if it were
evaluated.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
some $x in $expr1 satisfies $x = 47
</pre></div>
</div>
</li>
<li>
<p>In the following example, if an implementation can find (for
example, by using an index) the <code>product</code> element-nodes
that have an <code>id</code> child with the value <code>47</code>,
it is allowed to return these nodes as the result of the <a title=
"path expression" href="#dt-path-expression">path expression</a>,
without searching for another <code>product</code> node that would
raise an error because it has an <code>id</code> child whose value
is not an integer.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
//product[id = 47]
</pre></div>
</div>
</li>
</ul>
<p>For a variety of reasons, including optimization,
implementations may rewrite expressions into a different form.
There are a number of rules that limit the extent of this
freedom:</p>
<ul>
<li>
<p>Other than the raising or not raising of errors, the result of
evaluating a rewritten expression must conform to the semantics
defined in this specification for the original expression.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>This allows an implementation to return a result in cases where
the original expression would have raised an error, or to raise an
error in cases where the original expression would have returned a
result. The main cases where this is likely to arise in practice
are (a) where a rewrite changes the order of evaluation, such that
a subexpression causing an error is evaluated when the expression
is written one way and is not evaluated when the expression is
written a different way, and (b) where intermediate results of the
evaluation cause overflow or other out-of-range conditions.</p>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>This rule does not mean that the result of the expression will
always be the same in non-error cases as if it had not been
rewritten, because there are many cases where the result of an
expression is to some degree <a title="implementation dependent"
href="#dt-implementation-dependent">implementation-dependent</a> or
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
</div>
</li>
<li>
<p>Conditional and typeswitch expressions must not raise a dynamic
error in respect of subexpressions occurring in a branch that is
not selected, and must not return the value delivered by a branch
unless that branch is selected. Thus, the following example must
not raise a dynamic error if the document <code>abc.xml</code> does
not exist:</p>
<div class="exampleInner">
<pre>
if (doc-available('abc.xml')) then doc('abc.xml') else ()
</pre></div>
</li>
<li>
<p>As stated earlier, an expression must not be rewritten to
dispense with a required cardinality check: for example,
<code>string-length(//title)</code> must raise an error if the
document contains more than one title element.</p>
</li>
<li>
<p>Expressions must not be rewritten in such a way as to create or
remove static errors. For example, there is a rule that in casting
a string to a QName the operand must be a string literal. This rule
applies to the original expression and not to any rewritten form of
the expression.</p>
</li>
</ul>
<p>Expression rewrite is illustrated by the following examples.</p>
<ul>
<li>
<p>Consider the expression <code>//part[color eq "Red"]</code>. An
implementation might choose to rewrite this expression as
<code>//part[color = "Red"][color eq "Red"]</code>. The
implementation might then process the expression as follows: First
process the "<code>=</code>" predicate by probing an index on parts
by color to quickly find all the parts that have a Red color; then
process the "<code>eq</code>" predicate by checking each of these
parts to make sure it has only a single color. The result would be
as follows:</p>
<ul>
<li>
<p>Parts that have exactly one color that is Red are returned.</p>
</li>
<li>
<p>If some part has color Red together with some other color, an
error is raised.</p>
</li>
<li>
<p>The existence of some part that has no color Red but has
multiple non-Red colors does not trigger an error.</p>
</li>
</ul>
</li>
<li>
<p>The expression in the following example cannot raise a casting
error if it is evaluated exactly as written (i.e., left to right).
Since neither predicate depends on the context position, an
implementation might choose to reorder the predicates to achieve
better performance (for example, by taking advantage of an index).
This reordering could cause the expression to raise an error.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$N[@x castable as xs:date][xs:date(@x) gt xs:date("2000-01-01")]
</pre></div>
</div>
<p>To avoid unexpected errors caused by expression rewrite, tests
that are designed to prevent dynamic errors should be expressed
using conditional <span class="xquery"><span class="xquery">or
<code>typeswitch</code></span></span> expressions. For example, the
above expression can be written as follows:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$N[if (@x castable as xs:date)
   then xs:date(@x) gt xs:date("2000-01-01")
   else false()]
</pre></div>
</div>
</li>
</ul>
</div>
</div>
<div class="div2">
<h3><a name="id-important-concepts" id=
"id-important-concepts"></a>2.4 Concepts</h3>
<p>This section explains some concepts that are important to the
processing of XQuery expressions.</p>
<div class="div3">
<h4><a name="id-document-order" id="id-document-order"></a>2.4.1
Document Order</h4>
<p>An ordering called <b>document order</b> is defined among all
the nodes accessible during processing of a given <span class=
"xquery"><span class="xquery">query</span></span>, which may
consist of one or more <b>trees</b> (documents or fragments).
Document order is defined in <a href="#datamodel">[XQuery 1.0 and
XPath 2.0 Data Model (Second Edition)]</a>, and its definition is
repeated here for convenience. [<a name="dt-reverse-document-order"
id="dt-reverse-document-order" title=
"reverse document order">Definition</a>: The node ordering that is
the reverse of document order is called <b>reverse document
order</b>.]</p>
<p>Document order is a total ordering, although the relative order
of some nodes is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.
[<a name="dt-document-order" id="dt-document-order" title=
"document order">Definition</a>: Informally, <b>document order</b>
is the order in which nodes appear in the XML serialization of a
document.] [<a name="stable" id="stable" title=
"stable">Definition</a>: Document order is <b>stable</b>, which
means that the relative order of two nodes will not change during
the processing of a given <span class="xquery"><span class=
"xquery">query</span></span>, even if this order is <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.]</p>
<p>Within a tree, document order satisfies the following
constraints:</p>
<ol class="enumar">
<li>
<p>The root node is the first node.</p>
</li>
<li>
<p>Every node occurs before all of its children and
descendants.</p>
</li>
<li>
<p>Attribute nodes immediately follow the element node with which
they are associated. The relative order of attribute nodes is
stable but <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
</li>
<li>
<p>The relative order of siblings is the order in which they occur
in the <code>children</code> property of their parent node.</p>
</li>
<li>
<p>Children and descendants occur before following siblings.</p>
</li>
</ol>
<p>The relative order of nodes in distinct trees is stable but
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>,
subject to the following constraint: If any node in a given tree T1
is before any node in a different tree T2, then all nodes in tree
T1 are before all nodes in tree T2.</p>
</div>
<div class="div3">
<h4><a name="id-atomization" id="id-atomization"></a>2.4.2
Atomization</h4>
<p>The semantics of some XQuery operators depend on a process
called <a title="atomization" href=
"#dt-atomization">atomization</a>. Atomization is applied to a
value when the value is used in a context in which a sequence of
atomic values is required. The result of atomization is either a
sequence of atomic values or a <a title="type error" href=
"#dt-type-error">type error</a> [err:FOTY0012]. [<a name=
"dt-atomization" id="dt-atomization" title=
"atomization">Definition</a>: <b>Atomization</b> of a sequence is
defined as the result of invoking the <code>fn:data</code> function
on the sequence, as defined in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.]</p>
<p>The semantics of <code>fn:data</code> are repeated here for
convenience. The result of <code>fn:data</code> is the sequence of
atomic values produced by applying the following rules to each item
in the input sequence:</p>
<ul>
<li>
<p>If the item is an atomic value, it is returned.</p>
</li>
<li>
<p>If the item is a node, its <a title="typed value" href=
"#dt-typed-value">typed value</a> is returned (err:FOTY0012 is
raised if the node has no typed value.)</p>
</li>
</ul>
<p>Atomization is used in processing the following types of
expressions:</p>
<ul>
<li>
<p>Arithmetic expressions</p>
</li>
<li>
<p>Comparison expressions</p>
</li>
<li>
<p>Function calls and returns</p>
</li>
<li>
<p>Cast expressions</p>
</li>
<li class="xquery">
<p>Constructor expressions for various kinds of nodes</p>
</li>
<li class="xquery">
<p><code>order by</code> clauses in FLWOR expressions</p>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="id-ebv" id="id-ebv"></a>2.4.3 Effective Boolean
Value</h4>
<p>Under certain circumstances (listed below), it is necessary to
find the <a title="effective boolean value" href=
"#dt-ebv">effective boolean value</a> of a value. [<a name="dt-ebv"
id="dt-ebv" title="effective boolean value">Definition</a>: The
<b>effective boolean value</b> of a value is defined as the result
of applying the <code>fn:boolean</code> function to the value, as
defined in <a href="#FunctionsAndOperators">[XQuery 1.0 and XPath
2.0 Functions and Operators (Second Edition)]</a>.]</p>
<p>The dynamic semantics of <code>fn:boolean</code> are repeated
here for convenience:</p>
<ol class="enumar">
<li>
<p>If its operand is an empty sequence, <code>fn:boolean</code>
returns <code>false</code>.</p>
</li>
<li>
<p>If its operand is a sequence whose first item is a node,
<code>fn:boolean</code> returns <code>true</code>.</p>
</li>
<li>
<p>If its operand is a <a title="singleton" href=
"#dt-singleton">singleton</a> value of type <code>xs:boolean</code>
or derived from <code>xs:boolean</code>, <code>fn:boolean</code>
returns the value of its operand unchanged.</p>
</li>
<li>
<p>If its operand is a <a title="singleton" href=
"#dt-singleton">singleton</a> value of type <code>xs:string</code>,
<code>xs:anyURI</code>, <code>xs:untypedAtomic</code>, or a type
derived from one of these, <code>fn:boolean</code> returns
<code>false</code> if the operand value has zero length; otherwise
it returns <code>true</code>.</p>
</li>
<li>
<p>If its operand is a <a title="singleton" href=
"#dt-singleton">singleton</a> value of any <a title="numeric" href=
"#dt-numeric">numeric</a> type or derived from a numeric type,
<code>fn:boolean</code> returns <code>false</code> if the operand
value is <code>NaN</code> or is numerically equal to zero;
otherwise it returns <code>true</code>.</p>
</li>
<li>
<p>In all other cases, <code>fn:boolean</code> raises a type error
[err:FORG0006].</p>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The static semantics of <code>fn:boolean</code> are defined in
<a href=
"http://www.w3.org/TR/xquery-semantics/#sec_fn_boolean">Section
7.2.4 The fn:boolean and fn:not
functions</a><sup><small>FS</small></sup>.</p>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The <a title="effective boolean value" href="#dt-ebv">effective
boolean value</a> of a sequence that contains at least one node and
at least one atomic value may be nondeterministic in regions of a
query where <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is
<code>unordered</code>.</p>
</div>
<p>The <a title="effective boolean value" href="#dt-ebv">effective
boolean value</a> of a sequence is computed implicitly during
processing of the following types of expressions:</p>
<ul>
<li>
<p>Logical expressions (<code>and</code>, <code>or</code>)</p>
</li>
<li>
<p>The <code>fn:not</code> function</p>
</li>
<li class="xquery">
<p>The <code>where</code> clause of a FLWOR expression</p>
</li>
<li>
<p>Certain types of <a title="predicate" href=
"#dt-predicate">predicates</a>, such as <code>a[b]</code></p>
</li>
<li>
<p>Conditional expressions (<code>if</code>)</p>
</li>
<li>
<p>Quantified expressions (<code>some</code>,
<code>every</code>)</p>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The definition of <a title="effective boolean value" href=
"#dt-ebv">effective boolean value</a> is <em>not</em> used when
casting a value to the type <code>xs:boolean</code>, for example in
a <code>cast</code> expression or when passing a value to a
function whose expected parameter is of type
<code>xs:boolean</code>.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-input-sources" id="id-input-sources"></a>2.4.4
Input Sources</h4>
<p>XQuery has a set of functions that provide access to input data.
These functions are of particular importance because they provide a
way in which an expression can reference a document or a collection
of documents. The input functions are described informally here;
they are defined in <a href="#FunctionsAndOperators">[XQuery 1.0
and XPath 2.0 Functions and Operators (Second Edition)]</a>.</p>
<p>An expression can access input data either by calling one of the
input functions or by referencing some part of the <a title=
"dynamic context" href="#dt-dynamic-context">dynamic context</a>
that is initialized by the external environment, such as a
<a title="variable values" href="#dt-variable-values">variable</a>
or <a title="context item" href="#dt-context-item">context
item</a>.</p>
<p>The input functions supported by XQuery are as follows:</p>
<ul>
<li>
<p>The <code>fn:doc</code> function takes a string containing a
URI. If that URI is associated with a document in <a title=
"available documents" href="#dt-available-docs">available
documents</a>, <code>fn:doc</code> returns a document node whose
content is the <a title="data model" href="#dt-datamodel">data
model</a> representation of the given document; otherwise it raises
a <a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a> (see <a href="#FunctionsAndOperators">[XQuery 1.0 and
XPath 2.0 Functions and Operators (Second Edition)]</a> for
details).</p>
</li>
<li>
<p>The <code>fn:collection</code> function with one argument takes
a string containing a URI. If that URI is associated with a
collection in <a title="available collections" href=
"#dt-available-collections">available collections</a>,
<code>fn:collection</code> returns the data model representation of
that collection; otherwise it raises a <a title="dynamic error"
href="#dt-dynamic-error">dynamic error</a> (see <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a> for details). A collection may be
any sequence of nodes. For example, the expression
<code>fn:collection("http://example.org")//customer</code>
identifies all the <code>customer</code> elements that are
descendants of nodes found in the collection whose URI is
<code>http://example.org</code>.</p>
</li>
<li>
<p>The <code>fn:collection</code> function with zero arguments
returns the <a title="default collection" href=
"#dt-default-collection">default collection</a>, an <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
sequence of nodes.</p>
</li>
</ul>
</div>
<div class="xquery">
<div class="div3">
<h4><a name="id-uri-literals" id="id-uri-literals"></a>2.4.5 URI
Literals</h4>
<p>In certain places in the XQuery grammar, a statically known
valid URI is required. These places are denoted by the grammatical
symbol <a href="#doc-xquery-URILiteral">URILiteral</a>. For
example, URILiterals are used to specify namespaces and collations,
both of which must be statically known.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-URILiteral" id=
"doc-xquery-URILiteral"></a>[140]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-URILiteral" class=
"xquery">URILiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-StringLiteral">StringLiteral</a></code></td>
</tr>
</tbody>
</table>
<p>Syntactically, a URILiteral is identical to a <a href=
"#doc-xquery-StringLiteral">StringLiteral</a>: a sequence of zero
or more characters enclosed in single or double quotes. However, an
implementation <a title="may" href="#may">MAY</a> raise a <a title=
"static error" href="#dt-static-error">static error</a> [<a href=
"#ERRXQST0046" title="err:XQST0046">err:XQST0046</a>] if the value
of a URILiteral is of nonzero length and is not in the lexical
space of <code>xs:anyURI</code>.</p>
<p>As in a string literal, any <a title=
"predefined entity reference" href=
"#dt-predefined-entity-reference">predefined entity reference</a>
(such as <code>&amp;amp;</code>), <a title="character reference"
href="#dt-character-reference">character reference</a> (such as
<code>&amp;#x2022;</code>), or <a href=
"#doc-xquery-EscapeQuot">EscapeQuot</a> or <a href=
"#doc-xquery-EscapeApos">EscapeApos</a> (for example,
<code>""</code>) is replaced by its appropriate expansion. Certain
characters, notably the ampersand, can only be represented using a
<a title="predefined entity reference" href=
"#dt-predefined-entity-reference">predefined entity reference</a>
or a <a title="character reference" href=
"#dt-character-reference">character reference</a>.</p>
<p>The URILiteral is subjected to whitespace normalization as
defined for the <code>xs:anyURI</code> type in <a href=
"#XMLSchema">[XML Schema]</a>: this means that leading and trailing
whitespace is removed, and any other sequence of whitespace
characters is replaced by a single space (#x20) character.
Whitespace normalization is done after the expansion of <a title=
"character reference" href="#dt-character-reference">character
references</a>, so writing a newline (for example) as
<code>&amp;#xA;</code> does not prevent its being normalized to a
space character.</p>
<p>The URILiteral is not automatically subjected to
percent-encoding or decoding as defined in <a href=
"#RFC3986">[RFC3986]</a>. Any process that attempts to resolve the
URI against a base URI, or to dereference the URI, may however
apply percent-encoding or decoding as defined in the relevant
RFCs.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The <code>xs:anyURI</code> type is designed to anticipate the
introduction of Internationalized Resource Identifiers (IRI's) as
defined in <a href="#RFC3987">[RFC3987]</a>.</p>
</div>
<p>The following is an example of a valid URILiteral:</p>
<div class="exampleInner">
<pre>
"http://www.w3.org/2005/xpath-functions/collation/codepoint"
</pre></div>
</div>
</div>
</div>
<div class="div2">
<h3><a name="id-types" id="id-types"></a>2.5 Types</h3>
<p>The type system of XQuery is based on <a href="#XMLSchema">[XML
Schema]</a>, and is formally defined in <a href=
"#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal Semantics
(Second Edition)]</a>.</p>
<p>[<a name="dt-sequence-type" id="dt-sequence-type" title=
"sequence type">Definition</a>: A <b>sequence type</b> is a type
that can be expressed using the <a href=
"#doc-xquery-SequenceType">SequenceType</a> syntax. Sequence types
are used whenever it is necessary to refer to a type in an XQuery
expression. The term <b>sequence type</b> suggests that this syntax
is used to describe the type of an XQuery value, which is always a
sequence.]</p>
<p>[<a name="dt-schema-type" id="dt-schema-type" title=
"schema type">Definition</a>: A <b>schema type</b> is a type that
is (or could be) defined using the facilities of <a href=
"#XMLSchema">[XML Schema]</a> (including the built-in types of
<a href="#XMLSchema">[XML Schema]</a>).] A schema type can be used
as a type annotation on an element or attribute node (unless it is
a non-instantiable type such as <code>xs:NOTATION</code> or
<code>xs:anyAtomicType</code>, in which case its derived types can
be so used). Every schema type is either a <b>complex type</b> or a
<b>simple type</b>; simple types are further subdivided into
<b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see
<a href="#XMLSchema">[XML Schema]</a> for definitions and
explanations of these terms.)</p>
<p>Atomic types represent the intersection between the categories
of <a title="sequence type" href="#dt-sequence-type">sequence
type</a> and <a title="schema type" href="#dt-schema-type">schema
type</a>. An atomic type, such as <code>xs:integer</code> or
<code>my:hatsize</code>, is both a <a title="sequence type" href=
"#dt-sequence-type">sequence type</a> and a <a title="schema type"
href="#dt-schema-type">schema type</a>.</p>
<div class="div3">
<h4><a name="id-predefined-types" id=
"id-predefined-types"></a>2.5.1 Predefined Schema Types</h4>
<div class="xquery">
<p class="xquery">The <a title="in-scope schema type" href=
"#dt-is-types">in-scope schema types</a> in the <a title=
"static context" href="#dt-static-context">static context</a> are
initialized with certain predefined schema types, including the
built-in schema types in the namespace
<code>http://www.w3.org/2001/XMLSchema</code>, which has the
predefined namespace prefix <code>xs</code>. The schema types in
this namespace are defined in <a href="#XMLSchema">[XML Schema]</a>
and augmented by additional types defined in <a href=
"#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a>. Element and attribute declarations in the
<code>xs</code> namespace are not implicitly included in the static
context. The schema types defined in <a href="#datamodel">[XQuery
1.0 and XPath 2.0 Data Model (Second Edition)]</a> are summarized
below.</p>
</div>
<ol class="enumar">
<li>
<p>[<a name="dt-untyped" id="dt-untyped" title=
"xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the
<a title="type annotation" href="#dt-type-annotation">type
annotation</a> of an element node that has not been validated, or
has been validated in <code>skip</code> mode.] No predefined schema
types are derived from <code>xs:untyped</code>.</p>
</li>
<li>
<p>[<a name="dt-untypedAtomic" id="dt-untypedAtomic" title=
"xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is
an atomic type that is used to denote untyped atomic data, such as
text that has not been assigned a more specific type.] An attribute
that has been validated in <code>skip</code> mode is represented in
the <a title="data model" href="#dt-datamodel">data model</a> by an
attribute node with the <a title="type annotation" href=
"#dt-type-annotation">type annotation</a>
<code>xs:untypedAtomic</code>. No predefined schema types are
derived from <code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>[<a name="dt-dayTimeDuration" id="dt-dayTimeDuration" title=
"xs:dayTimeDuration">Definition</a>:
<code>xs:dayTimeDuration</code> is derived by restriction from
<code>xs:duration</code>. The lexical representation of
<code>xs:dayTimeDuration</code> is restricted to contain only day,
hour, minute, and second components.]</p>
</li>
<li>
<p>[<a name="dt-yearMonthDuration" id="dt-yearMonthDuration" title=
"xs:yearMonthDuration">Definition</a>:
<code>xs:yearMonthDuration</code> is derived by restriction from
<code>xs:duration</code>. The lexical representation of
<code>xs:yearMonthDuration</code> is restricted to contain only
year and month components.]</p>
</li>
<li>
<p>[<a name="dt-anyAtomicType" id="dt-anyAtomicType" title=
"xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is
an atomic type that includes all atomic values (and no values that
are not atomic). Its base type is <code>xs:anySimpleType</code>
from which all simple types, including atomic, list, and union
types, are derived. All primitive atomic types, such as
<code>xs:decimal</code> and <code>xs:string</code>, have
<code>xs:anyAtomicType</code> as their base type.]</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p><code>xs:anyAtomicType</code> will not appear as the type of an
actual value in an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a>.</p>
</div>
</li>
</ol>
<p>The relationships among the schema types in the <code>xs</code>
namespace are illustrated in Figure 2. A more complete description
of the XQuery type hierarchy can be found in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
<img src="types.jpg" alt="Type Hierarchy Diagram" />
<p>Figure 2: Hierarchy of Schema Types used in XQuery</p>
</div>
<div class="div3">
<h4><a name="id-typed-value" id="id-typed-value"></a>2.5.2 Typed
Value and String Value</h4>
<p>Every node has a <b>typed value</b> and a <b>string value</b>.
[<a name="dt-typed-value" id="dt-typed-value" title=
"typed value">Definition</a>: The <b>typed value</b> of a node is a
sequence of atomic values and can be extracted by applying the
<code>fn:data</code> function to the node.] [<a name=
"dt-string-value" id="dt-string-value" title=
"string value">Definition</a>: The <b>string value</b> of a node is
a string and can be extracted by applying the
<code>fn:string</code> function to the node.] Definitions of
<code>fn:data</code> and <code>fn:string</code> can be found in
<a href="#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0
Functions and Operators (Second Edition)]</a>.</p>
<p>An implementation may store both the <a title="typed value"
href="#dt-typed-value">typed value</a> and the <a title=
"string value" href="#dt-string-value">string value</a> of a node,
or it may store only one of these and derive the other as needed.
The string value of a node must be a valid lexical representation
of the typed value of the node, but the node is not required to
preserve the string representation from the original source
document. For example, if the typed value of a node is the
<code>xs:integer</code> value <code>30</code>, its string value
might be "<code>30</code>" or "<code>0030</code>".</p>
<div class="xquery">
<p class="xquery">The <a title="typed value" href=
"#dt-typed-value">typed value</a>, <a title="string value" href=
"#dt-string-value">string value</a>, and <a title="type annotation"
href="#dt-type-annotation">type annotation</a> of a node are
closely related, and are defined by rules found in the following
locations:</p>
</div>
<ul>
<li>
<p>If the node was created by mapping from an Infoset or PSVI, see
rules in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data Model
(Second Edition)]</a>.</p>
</li>
<li>
<p>If the node was created by an XQuery node constructor, see rules
in <a href="#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a>, <a href="#id-computedElements"><b>3.7.3.1
Computed Element Constructors</b></a>, or <a href=
"#id-computedAttributes"><b>3.7.3.2 Computed Attribute
Constructors</b></a>.</p>
</li>
<li>
<p>If the node was created by a <code>validate</code> expression,
see rules in <a href="#id-validate"><b>3.13 Validate
Expressions</b></a>.</p>
</li>
</ul>
<p>As a convenience to the reader, the relationship between
<a title="typed value" href="#dt-typed-value">typed value</a> and
<a title="string value" href="#dt-string-value">string value</a>
for various kinds of nodes is summarized and illustrated by
examples below.</p>
<ol class="enumar">
<li>
<p>For text and document nodes, the typed value of the node is the
same as its string value, as an instance of the type
<code>xs:untypedAtomic</code>. The string value of a document node
is formed by concatenating the string values of all its descendant
text nodes, in <a title="document order" href=
"#dt-document-order">document order</a>.</p>
</li>
<li>
<p>The typed value of a comment or processing instruction node is
the same as its string value. It is an instance of the type
<code>xs:string</code>.</p>
</li>
<li>
<p>The typed value of an attribute node with the <a title=
"type annotation" href="#dt-type-annotation">type annotation</a>
<code>xs:anySimpleType</code> or <code>xs:untypedAtomic</code> is
the same as its string value, as an instance of
<code>xs:untypedAtomic</code>. The typed value of an attribute node
with any other type annotation is derived from its string value and
type annotation using the lexical-to-value-space mapping defined in
<a href="#XMLSchema">[XML Schema]</a> Part 2 for the relevant
type.</p>
<p>Example: A1 is an attribute having string value
<code>"3.14E-2"</code> and type annotation <code>xs:double</code>.
The typed value of A1 is the <code>xs:double</code> value whose
lexical representation is <code>3.14E-2</code>.</p>
<p>Example: A2 is an attribute with type annotation
<code>xs:IDREFS</code>, which is a list datatype whose item type is
the atomic datatype <code>xs:IDREF</code>. Its string value is
"<code>bar baz faz</code>". The typed value of A2 is a sequence of
three atomic values ("<code>bar</code>", "<code>baz</code>",
"<code>faz</code>"), each of type <code>xs:IDREF</code>. The typed
value of a node is never treated as an instance of a named list
type. Instead, if the type annotation of a node is a list type
(such as <code>xs:IDREFS</code>), its typed value is treated as a
sequence of the atomic type from which it is derived (such as
<code>xs:IDREF</code>).</p>
</li>
<li>
<p>For an element node, the relationship between typed value and
string value depends on the node's <a title="type annotation" href=
"#dt-type-annotation">type annotation</a>, as follows:</p>
<ol class="enumla">
<li>
<p>If the type annotation is <code>xs:untyped</code> or
<code>xs:anySimpleType</code> or denotes a complex type with mixed
content (including <code>xs:anyType</code>), then the typed value
of the node is equal to its string value, as an instance of
<code>xs:untypedAtomic</code>. However, if the <code>nilled</code>
property of the node is <code>true</code>, then its typed value is
the empty sequence.</p>
<p>Example: E1 is an element node having type annotation
<code>xs:untyped</code> and string value "<code>1999-05-31</code>".
The typed value of E1 is "<code>1999-05-31</code>", as an instance
of <code>xs:untypedAtomic</code>.</p>
<p>Example: E2 is an element node with the type annotation
<code>formula</code>, which is a complex type with mixed content.
The content of E2 consists of the character "<code>H</code>", a
child element named <code>subscript</code> with string value
"<code>2</code>", and the character "<code>O</code>". The typed
value of E2 is "<code>H2O</code>" as an instance of
<code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>If the type annotation denotes a simple type or a complex type
with simple content, then the typed value of the node is derived
from its string value and its type annotation in a way that is
consistent with schema validation. However, if the
<code>nilled</code> property of the node is <code>true</code>, then
its typed value is the empty sequence.</p>
<p>Example: E3 is an element node with the type annotation
<code>cost</code>, which is a complex type that has several
attributes and a simple content type of <code>xs:decimal</code>.
The string value of E3 is "<code>74.95</code>". The typed value of
E3 is <code>74.95</code>, as an instance of
<code>xs:decimal</code>.</p>
<p>Example: E4 is an element node with the type annotation
<code>hatsizelist</code>, which is a simple type derived from the
atomic type <code>hatsize</code>, which in turn is derived from
<code>xs:integer</code>. The string value of E4 is "<code>7 8
9</code>". The typed value of E4 is a sequence of three values
(<code>7</code>, <code>8</code>, <code>9</code>), each of type
<code>hatsize</code>.</p>
<p>Example: E5 is an element node with the type annotation
<code>my:integer-or-string</code> which is a union type with member
types <code>xs:integer</code> and <code>xs:string</code>. The
string value of E5 is "<code>47</code>". The typed value of E5 is
<code>47</code> as an <code>xs:integer</code>, since
<code>xs:integer</code> is the member type that validated the
content of E5. In general, when the type annotation of a node is a
union type, the typed value of the node will be an instance of one
of the member types of the union.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>If an implementation stores only the string value of a node, and
the type annotation of the node is a union type, the implementation
must be able to deliver the typed value of the node as an instance
of the appropriate member type.</p>
</div>
</li>
<li>
<p>If the type annotation denotes a complex type with empty
content, then the typed value of the node is the empty sequence and
its string value is the zero-length string.</p>
</li>
<li>
<p>If the type annotation denotes a complex type with element-only
content, then the typed value of the node is <a title="undefined"
href="#dt-undefined">undefined</a>. The <code>fn:data</code>
function raises a <a title="type error" href="#dt-type-error">type
error</a> [err:FOTY0012] when applied to such a node. The string
value of such a node is equal to the concatenated string values of
all its text node descendants, in document order.</p>
<p>Example: E6 is an element node with the type annotation
<code>weather</code>, which is a complex type whose content type
specifies <code>element-only</code>. E6 has two child elements
named <code>temperature</code> and <code>precipitation</code>. The
typed value of E6 is <a title="undefined" href=
"#dt-undefined">undefined</a>, and the <code>fn:data</code>
function applied to E6 raises an error.</p>
</li>
</ol>
</li>
</ol>
</div>
<div class="div3">
<h4><a name="id-sequencetype-syntax" id=
"id-sequencetype-syntax"></a>2.5.3 SequenceType Syntax</h4>
<p>Whenever it is necessary to refer to a type in an XQuery
expression, the <a href="#doc-xquery-SequenceType">SequenceType</a>
syntax is used.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-SequenceType" id=
"doc-xquery-SequenceType"></a>[119]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-SequenceType">SequenceType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("empty-sequence" "(" ")")<br />
| (<a href="#doc-xquery-ItemType">ItemType</a> <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a>?)</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ItemType" id=
"doc-xquery-ItemType"></a>[121]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ItemType">ItemType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-KindTest">KindTest</a> | ("item" "("
")") | <a href="#doc-xquery-AtomicType">AtomicType</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OccurrenceIndicator" id=
"doc-xquery-OccurrenceIndicator"></a>[120]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-OccurrenceIndicator">OccurrenceIndicator</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"?" | "*" | "+"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AtomicType" id=
"doc-xquery-AtomicType"></a>[122]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AtomicType">AtomicType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-KindTest" id=
"doc-xquery-KindTest"></a>[123]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-KindTest">KindTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-DocumentTest">DocumentTest</a><br />
| <a href="#doc-xquery-ElementTest">ElementTest</a><br />
| <a href="#doc-xquery-AttributeTest">AttributeTest</a><br />
| <a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a><br />
| <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a><br />
| <a href="#doc-xquery-PITest">PITest</a><br />
| <a href="#doc-xquery-CommentTest">CommentTest</a><br />
| <a href="#doc-xquery-TextTest">TextTest</a><br />
| <a href="#doc-xquery-AnyKindTest">AnyKindTest</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DocumentTest" id=
"doc-xquery-DocumentTest"></a>[125]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DocumentTest">DocumentTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"document-node" "(" (<a href=
"#doc-xquery-ElementTest">ElementTest</a> | <a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a>)?
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ElementTest" id=
"doc-xquery-ElementTest"></a>[133]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ElementTest">ElementTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"element" "(" (<a href=
"#doc-xquery-ElementNameOrWildcard">ElementNameOrWildcard</a> (","
<a href="#doc-xquery-TypeName">TypeName</a> "?"?)?)?
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-SchemaElementTest" id=
"doc-xquery-SchemaElementTest"></a>[135]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-SchemaElementTest">SchemaElementTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"schema-element" "(" <a href=
"#doc-xquery-ElementDeclaration">ElementDeclaration</a>
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ElementDeclaration" id=
"doc-xquery-ElementDeclaration"></a>[136]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ElementDeclaration">ElementDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ElementName">ElementName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AttributeTest" id=
"doc-xquery-AttributeTest"></a>[129]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AttributeTest">AttributeTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"attribute" "(" (<a href=
"#doc-xquery-AttribNameOrWildcard">AttribNameOrWildcard</a> (","
<a href="#doc-xquery-TypeName">TypeName</a>)?)? ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-SchemaAttributeTest" id=
"doc-xquery-SchemaAttributeTest"></a>[131]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-SchemaAttributeTest">SchemaAttributeTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"schema-attribute" "(" <a href=
"#doc-xquery-AttributeDeclaration">AttributeDeclaration</a>
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AttributeDeclaration" id=
"doc-xquery-AttributeDeclaration"></a>[132]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AttributeDeclaration">AttributeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AttributeName">AttributeName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ElementNameOrWildcard" id=
"doc-xquery-ElementNameOrWildcard"></a>[134]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ElementNameOrWildcard">ElementNameOrWildcard</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ElementName">ElementName</a> |
"*"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ElementName" id=
"doc-xquery-ElementName"></a>[138]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ElementName">ElementName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AttribNameOrWildcard" id=
"doc-xquery-AttribNameOrWildcard"></a>[130]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AttribNameOrWildcard">AttribNameOrWildcard</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AttributeName">AttributeName</a> |
"*"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AttributeName" id=
"doc-xquery-AttributeName"></a>[137]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AttributeName">AttributeName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-TypeName" id=
"doc-xquery-TypeName"></a>[139]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TypeName">TypeName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PITest" id=
"doc-xquery-PITest"></a>[128]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-PITest">PITest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"processing-instruction" "(" (<a href=
"#prod-xquery-NCName">NCName</a> | <a href=
"#doc-xquery-StringLiteral">StringLiteral</a>)? ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CommentTest" id=
"doc-xquery-CommentTest"></a>[127]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-CommentTest">CommentTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"comment" "(" ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-TextTest" id=
"doc-xquery-TextTest"></a>[126]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TextTest">TextTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"text" "(" ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AnyKindTest" id=
"doc-xquery-AnyKindTest"></a>[124]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AnyKindTest">AnyKindTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"node" "(" ")"</code></td>
</tr>
</tbody>
</table>
<p>With the exception of the special type
<code>empty-sequence()</code>, a <a title="sequence type" href=
"#dt-sequence-type">sequence type</a> consists of an <b>item
type</b> that constrains the type of each item in the sequence, and
a <b>cardinality</b> that constrains the number of items in the
sequence. Apart from the item type <code>item()</code>, which
permits any kind of item, item types divide into <b>node types</b>
(such as <code>element()</code>) and <b>atomic types</b> (such as
<code>xs:integer</code>).</p>
<p>Item types representing element and attribute nodes may specify
the required <a title="type annotation" href=
"#dt-type-annotation">type annotations</a> of those nodes, in the
form of a <a title="schema type" href="#dt-schema-type">schema
type</a>. Thus the item type <code>element(*, us:address)</code>
denotes any element node whose type annotation is (or is derived
from) the schema type named <code>us:address</code>.</p>
<p>Here are some examples of <a title="sequence type" href=
"#dt-sequence-type">sequence types</a> that might be used in XQuery
expressions:</p>
<ul>
<li>
<p><code>xs:date</code> refers to the built-in atomic schema type
named <code>xs:date</code></p>
</li>
<li>
<p><code>attribute()?</code> refers to an optional attribute
node</p>
</li>
<li>
<p><code>element()</code> refers to any element node</p>
</li>
<li>
<p><code>element(po:shipto, po:address)</code> refers to an element
node that has the name <code>po:shipto</code> and has the type
annotation <code>po:address</code> (or a schema type derived from
<code>po:address</code>)</p>
</li>
<li>
<p><code>element(*, po:address)</code> refers to an element node of
any name that has the type annotation <code>po:address</code> (or a
type derived from <code>po:address</code>)</p>
</li>
<li>
<p><code>element(customer)</code> refers to an element node named
<code>customer</code> with any type annotation</p>
</li>
<li>
<p><code>schema-element(customer)</code> refers to an element node
whose name is <code>customer</code> (or is in the substitution
group headed by <code>customer</code>) and whose type annotation
matches the schema type declared for a <code>customer</code>
element in the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a></p>
</li>
<li>
<p><code>node()*</code> refers to a sequence of zero or more nodes
of any kind</p>
</li>
<li>
<p><code>item()+</code> refers to a sequence of one or more nodes
or atomic values</p>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="id-sequencetype-matching" id=
"id-sequencetype-matching"></a>2.5.4 SequenceType Matching</h4>
<p>[<a name="dt-sequencetype-matching" id=
"dt-sequencetype-matching" title=
"SequenceType matching">Definition</a>: During evaluation of an
expression, it is sometimes necessary to determine whether a value
with a known <a title="dynamic type" href=
"#dt-dynamic-type">dynamic type</a> "matches" an expected <a title=
"sequence type" href="#dt-sequence-type">sequence type</a>. This
process is known as <b>SequenceType matching</b>.] For example, an
<code>instance of</code> expression returns <code>true</code> if
the <a title="dynamic type" href="#dt-dynamic-type">dynamic
type</a> of a given value matches a given <a title="sequence type"
href="#dt-sequence-type">sequence type</a>, or <code>false</code>
if it does not.</p>
<p>QNames appearing in a <a title="sequence type" href=
"#dt-sequence-type">sequence type</a> have their prefixes expanded
to namespace URIs by means of the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> and (where
applicable) the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a>. An
unprefixed attribute QName is in no namespace. Equality of QNames
is defined by the <code>eq</code> operator.</p>
<p>The rules for <a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a> compare the
<a title="dynamic type" href="#dt-dynamic-type">dynamic type</a> of
a value with an expected <a title="sequence type" href=
"#dt-sequence-type">sequence type</a>. These rules are a subset of
the formal rules that match a value with an expected type defined
in <a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0
Formal Semantics (Second Edition)]</a>, because the Formal
Semantics must be able to match values against types that are not
expressible using the <a href=
"#doc-xquery-SequenceType">SequenceType</a> syntax.</p>
<p>Some of the rules for <a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a> require
determining whether a given schema type is the same as or derived
from an expected schema type. The given schema type may be "known"
(defined in the <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a>), or "unknown" (not
defined in the <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a>). An unknown schema type
might be encountered, for example, if a source document has been
validated using a schema that was not imported into the <a title=
"static context" href="#dt-static-context">static context</a>. In
this case, an implementation is allowed (but is not required) to
provide an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
mechanism for determining whether the unknown schema type is
derived from the expected schema type. For example, an
implementation might maintain a data dictionary containing
information about type hierarchies.</p>
<p>[<a name="dt-subtype-substitution" id="dt-subtype-substitution"
title="subtype substitution">Definition</a>: The use of a value
whose <a title="dynamic type" href="#dt-dynamic-type">dynamic
type</a> is derived from an expected type is known as <b>subtype
substitution</b>.] Subtype substitution does not change the actual
type of a value. For example, if an <code>xs:integer</code> value
is used where an <code>xs:decimal</code> value is expected, the
value retains its type as <code>xs:integer</code>.</p>
<p>The definition of <a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a> relies on a
pseudo-function named <code>derives-from(</code><em>AT,
ET</em><code>)</code>, which takes an actual simple or complex
schema type <em>AT</em> and an expected simple or complex schema
type <em>ET</em>, and either returns a boolean value or raises a
<a title="type error" href="#dt-type-error">type error</a>
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. The
pseudo-function <code>derives-from</code> is defined below and is
defined formally in <a href="#XQueryFormalSemantics">[XQuery 1.0
and XPath 2.0 Formal Semantics (Second Edition)]</a>.</p>
<ul>
<li>
<p><code>derives-from(</code><em>AT</em>, <em>ET</em><code>)</code>
returns <code>true</code> if <em>ET</em> is a known type and any of
the following three conditions is true:</p>
<ol class="enumar">
<li>
<p><em>AT</em> is a schema type found in the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a>, and is the same as <em>ET</em> or is derived by
restriction or extension from <em>ET</em></p>
</li>
<li>
<p><em>AT</em> is a schema type not found in the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a>, and an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
mechanism is able to determine that <em>AT</em> is derived by
restriction from <em>ET</em></p>
</li>
<li>
<p>There exists some schema type <em>IT</em> such that
<code>derives-from(</code><em>IT, ET</em><code>)</code> and
<code>derives-from(</code><em>AT, IT</em><code>)</code> are
true.</p>
</li>
</ol>
</li>
<li>
<p><code>derives-from(</code><em>AT</em>, <em>ET</em><code>)</code>
returns <code>false</code> if <em>ET</em> is a known type and
either the first and third or the second and third of the following
conditions are true:</p>
<ol class="enumar">
<li>
<p><em>AT</em> is a schema type found in the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a>, and is not the same as <em>ET</em>, and is not
derived by restriction or extension from <em>ET</em></p>
</li>
<li>
<p><em>AT</em> is a schema type not found in the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a>, and an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
mechanism is able to determine that <em>AT</em> is not derived by
restriction from <em>ET</em></p>
</li>
<li>
<p>No schema type <em>IT</em> exists such that
<code>derives-from(</code><em>IT, ET</em><code>)</code> and
<code>derives-from(</code><em>AT, IT</em><code>)</code> are
true.</p>
</li>
</ol>
</li>
<li>
<p><code>derives-from(</code><em>AT</em>, <em>ET</em><code>)</code>
raises a <a title="type error" href="#dt-type-error">type error</a>
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]
if:</p>
<ol class="enumar">
<li>
<p><em>ET</em> is an unknown type, or</p>
</li>
<li>
<p><em>AT</em> is an unknown type, and the implementation is not
able to determine whether <em>AT</em> is derived by restriction
from <em>ET</em>.</p>
</li>
</ol>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The <code>derives-from</code> pseudo-function cannot be written
as a real XQuery function, because types are not valid function
parameters.</p>
</div>
<p>The rules for <a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a> are given
below, with examples (the examples are for purposes of
illustration, and do not cover all possible cases).</p>
<div class="div4">
<h5><a name="id-matching-value" id="id-matching-value"></a>2.5.4.1
Matching a SequenceType and a Value</h5>
<ul>
<li>
<p>The <a title="sequence type" href="#dt-sequence-type">sequence
type</a> <code>empty-sequence()</code> matches a value that is the
empty sequence.</p>
</li>
<li>
<p>An <a href="#doc-xquery-ItemType">ItemType</a> with no <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a> matches
any value that contains exactly one item if the <a href=
"#doc-xquery-ItemType">ItemType</a> matches that item (see <a href=
"#id-matching-item"><b>2.5.4.2 Matching an ItemType and an
Item</b></a>).</p>
</li>
<li>
<p>An <a href="#doc-xquery-ItemType">ItemType</a> with an <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a> matches a
value if the number of items in the value matches the <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a> and the
<a href="#doc-xquery-ItemType">ItemType</a> matches each of the
items in the value.</p>
</li>
</ul>
<p>An <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a> specifies
the number of items in a sequence, as follows:</p>
<ul>
<li>
<p><code>?</code> matches zero or one items</p>
</li>
<li>
<p><code>*</code> matches zero or more items</p>
</li>
<li>
<p><code>+</code> matches one or more items</p>
</li>
</ul>
<p>As a consequence of these rules, any <a title="sequence type"
href="#dt-sequence-type">sequence type</a> whose <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a> is
<code>*</code> or <code>?</code> matches a value that is an empty
sequence.</p>
</div>
<div class="div4">
<h5><a name="id-matching-item" id="id-matching-item"></a>2.5.4.2
Matching an ItemType and an Item</h5>
<ul>
<li>
<p>An <a href="#doc-xquery-ItemType">ItemType</a> consisting simply
of a QName is interpreted as an <a href=
"#doc-xquery-AtomicType">AtomicType</a>. An AtomicType
<em>AtomicType</em> matches an atomic value whose actual type is
<em>AT</em> if <code>derives-from(</code><em>AT,
AtomicType</em><code>)</code> is <code>true</code>. If a QName that
is used as an <a href="#doc-xquery-AtomicType">AtomicType</a> is
not defined as an atomic type in the <a title=
"in-scope schema type" href="#dt-is-types">in-scope schema
types</a>, a <a title="static error" href="#dt-static-error">static
error</a> is raised [<a href="#ERRXPST0051" title=
"err:XPST0051">err:XPST0051</a>].</p>
<p>Example: The <a href="#doc-xquery-AtomicType">AtomicType</a>
<code>xs:decimal</code> matches the value <code>12.34</code> (a
decimal literal). <code>xs:decimal</code> also matches a value
whose type is <code>shoesize</code>, if <code>shoesize</code> is an
atomic type derived by restriction from
<code>xs:decimal</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The names of non-atomic types such as <code>xs:IDREFS</code> are
not accepted in this context, but can often be replaced by an
atomic type with an occurrence indicator, such as
<code>xs:IDREF+</code>.</p>
</div>
</li>
<li>
<p><code>item()</code> matches any single item.</p>
<p>Example: <code>item()</code> matches the atomic value
<code>1</code> or the element <code>&lt;a/&gt;</code>.</p>
</li>
<li>
<p><code>node()</code> matches any node.</p>
</li>
<li>
<p><code>text()</code> matches any text node.</p>
</li>
<li>
<p><code>processing-instruction()</code> matches any
processing-instruction node.</p>
</li>
<li>
<p><code>processing-instruction(</code><em>N</em><code>)</code>
matches any processing-instruction node whose PITarget is equal to
<code>fn:normalize-space(N)</code>. If
<code>fn:normalize-space(N)</code> is not in the lexical space of
NCName, a type error is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>]</p>
<p>Example: <code>processing-instruction(xml-stylesheet)</code>
matches any processing instruction whose PITarget is
<code>xml-stylesheet</code>.</p>
<p>For backward compatibility with XPath 1.0, the PITarget of a
processing instruction may also be expressed as a string literal,
as in this example:
<code>processing-instruction("xml-stylesheet")</code>.</p>
</li>
<li>
<p><code>comment()</code> matches any comment node.</p>
</li>
<li>
<p><code>document-node()</code> matches any document node.</p>
</li>
<li>
<p><code>document-node(</code><em>E</em><code>)</code> matches any
document node that contains exactly one element node, optionally
accompanied by one or more comment and processing instruction
nodes, if <em>E</em> is an <a href=
"#doc-xquery-ElementTest">ElementTest</a> or <a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a> that matches
the element node (see <a href="#id-element-test"><b>2.5.4.3 Element
Test</b></a> and <a href="#id-schema-element-test"><b>2.5.4.4
Schema Element Test</b></a>).</p>
<p>Example: <code>document-node(element(book))</code> matches a
document node containing exactly one element node that is matched
by the ElementTest <code>element(book)</code>.</p>
</li>
<li>
<p>An <a href="#doc-xquery-ItemType">ItemType</a> that is an
<a href="#doc-xquery-ElementTest">ElementTest</a>, <a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a>, <a href=
"#doc-xquery-AttributeTest">AttributeTest</a>, or <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a> matches
an element or attribute node as described in the following
sections.</p>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="id-element-test" id="id-element-test"></a>2.5.4.3
Element Test</h5>
<p>An <a href="#doc-xquery-ElementTest">ElementTest</a> is used to
match an element node by its name and/or <a title="type annotation"
href="#dt-type-annotation">type annotation</a>. An <a href=
"#doc-xquery-ElementTest">ElementTest</a> may take any of the
following forms. In these forms, <a href=
"#doc-xquery-ElementName">ElementName</a> need not be present in
the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a>, but <a href=
"#doc-xquery-TypeName">TypeName</a> must be present in the
<a title="in-scope schema type" href="#dt-is-types">in-scope schema
types</a> [<a href="#ERRXPST0008" title=
"err:XPST0008">err:XPST0008</a>]. Note that <a title=
"substitution group" href="#dt-substitution-group">substitution
groups</a> do not affect the semantics of <a href=
"#doc-xquery-ElementTest">ElementTest</a>.</p>
<ol class="enumar">
<li>
<p><code>element()</code> and <code>element(*)</code> match any
single element node, regardless of its name or type annotation.</p>
</li>
<li>
<p><code>element(</code><a href=
"#doc-xquery-ElementName">ElementName</a><code>)</code> matches any
element node whose name is <a href=
"#doc-xquery-ElementName">ElementName</a>, regardless of its type
annotation or <code>nilled</code> property.</p>
<p>Example: <code>element(person)</code> matches any element node
whose name is <code>person</code>.</p>
</li>
<li>
<p><code>element(</code><a href=
"#doc-xquery-ElementName">ElementName</a><code>,</code> <a href=
"#doc-xquery-TypeName">TypeName</a><code>)</code> matches an
element node whose name is <a href=
"#doc-xquery-ElementName">ElementName</a> if
<code>derives-from(</code><em>AT</em>, <a href=
"#doc-xquery-TypeName">TypeName</a> <code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
element node, and the <code>nilled</code> property of the node is
<code>false</code>.</p>
<p>Example: <code>element(person, surgeon)</code> matches a
non-nilled element node whose name is <code>person</code> and whose
type annotation is <code>surgeon</code> (or is derived from
<code>surgeon</code>).</p>
</li>
<li>
<p><code>element(</code><a href=
"#doc-xquery-ElementName">ElementName</a>, <a href=
"#doc-xquery-TypeName">TypeName</a> <code>?)</code> matches an
element node whose name is <a href=
"#doc-xquery-ElementName">ElementName</a> if
<code>derives-from(</code><em>AT</em>, <a href=
"#doc-xquery-TypeName">TypeName</a><code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
element node. The <code>nilled</code> property of the node may be
either <code>true</code> or <code>false</code>.</p>
<p>Example: <code>element(person, surgeon?)</code> matches a nilled
or non-nilled element node whose name is <code>person</code> and
whose type annotation is <code>surgeon</code> (or is derived from
<code>surgeon</code>).</p>
</li>
<li>
<p><code>element(*,</code> <a href=
"#doc-xquery-TypeName">TypeName</a><code>)</code> matches an
element node regardless of its name, if
<code>derives-from(</code><em>AT</em>, <a href=
"#doc-xquery-TypeName">TypeName</a> <code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
element node, and the <code>nilled</code> property of the node is
<code>false</code>.</p>
<p>Example: <code>element(*, surgeon)</code> matches any non-nilled
element node whose type annotation is <code>surgeon</code> (or is
derived from <code>surgeon</code>), regardless of its name.</p>
</li>
<li>
<p><code>element(*,</code> <a href=
"#doc-xquery-TypeName">TypeName</a> <code>?)</code> matches an
element node regardless of its name, if
<code>derives-from(</code><em>AT</em>, <a href=
"#doc-xquery-TypeName">TypeName</a> <code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
element node. The <code>nilled</code> property of the node may be
either <code>true</code> or <code>false</code>.</p>
<p>Example: <code>element(*, surgeon?)</code> matches any nilled or
non-nilled element node whose type annotation is
<code>surgeon</code> (or is derived from <code>surgeon</code>),
regardless of its name.</p>
</li>
</ol>
</div>
<div class="div4">
<h5><a name="id-schema-element-test" id=
"id-schema-element-test"></a>2.5.4.4 Schema Element Test</h5>
<p>A <a href="#doc-xquery-SchemaElementTest">SchemaElementTest</a>
matches an element node against a corresponding element declaration
found in the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a>. It takes the
following form:</p>
<p><code>schema-element(</code><a href=
"#doc-xquery-ElementName">ElementName</a><code>)</code></p>
<p>If the <a href="#doc-xquery-ElementName">ElementName</a>
specified in the <a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a> is not found
in the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a>, a <a title=
"static error" href="#dt-static-error">static error</a> is raised
[<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>].</p>
<p>A <a href="#doc-xquery-SchemaElementTest">SchemaElementTest</a>
matches a candidate element node if all three of the following
conditions are satisfied:</p>
<ol class="enumar">
<li>
<p>The name of the candidate node matches the specified <a href=
"#doc-xquery-ElementName">ElementName</a> or matches the name of an
element in a <a title="substitution group" href=
"#dt-substitution-group">substitution group</a> headed by an
element named <a href=
"#doc-xquery-ElementName">ElementName</a>.</p>
</li>
<li>
<p><code>derives-from(</code><em>AT, ET</em><code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
candidate node and <em>ET</em> is the schema type declared for
element <a href="#doc-xquery-ElementName">ElementName</a> in the
<a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a>.</p>
</li>
<li>
<p>If the element declaration for <a href=
"#doc-xquery-ElementName">ElementName</a> in the <a title=
"in-scope element declarations" href="#dt-is-elems">in-scope
element declarations</a> is not <code>nillable</code>, then the
<code>nilled</code> property of the candidate node is
<code>false</code>.</p>
</li>
</ol>
<p>Example: The <a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a>
<code>schema-element(customer)</code> matches a candidate element
node if <code>customer</code> is a top-level element declaration in
the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a>, the name of the
candidate node is <code>customer</code> or is in a <a title=
"substitution group" href="#dt-substitution-group">substitution
group</a> headed by <code>customer</code>, the type annotation of
the candidate node is the same as or derived from the schema type
declared for the <code>customer</code> element, and either the
candidate node is not <code>nilled</code> or <code>customer</code>
is declared to be <code>nillable</code>.</p>
</div>
<div class="div4">
<h5><a name="id-attribute-test" id="id-attribute-test"></a>2.5.4.5
Attribute Test</h5>
<p>An <a href="#doc-xquery-AttributeTest">AttributeTest</a> is used
to match an attribute node by its name and/or <a title=
"type annotation" href="#dt-type-annotation">type annotation</a>.
An <a href="#doc-xquery-AttributeTest">AttributeTest</a> any take
any of the following forms. In these forms, <a href=
"#doc-xquery-AttributeName">AttributeName</a> need not be present
in the <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declarations</a>, but <a href=
"#doc-xquery-TypeName">TypeName</a> must be present in the
<a title="in-scope schema type" href="#dt-is-types">in-scope schema
types</a> [<a href="#ERRXPST0008" title=
"err:XPST0008">err:XPST0008</a>].</p>
<ol class="enumar">
<li>
<p><code>attribute()</code> and <code>attribute(*)</code> match any
single attribute node, regardless of its name or type
annotation.</p>
</li>
<li>
<p><code>attribute(</code><a href=
"#doc-xquery-AttributeName">AttributeName</a><code>)</code> matches
any attribute node whose name is <a href=
"#doc-xquery-AttributeName">AttributeName</a>, regardless of its
type annotation.</p>
<p>Example: <code>attribute(price)</code> matches any attribute
node whose name is <code>price</code>.</p>
</li>
<li>
<p><code>attribute(</code><a href=
"#doc-xquery-AttributeName">AttributeName</a>, <a href=
"#doc-xquery-TypeName">TypeName</a><code>)</code> matches an
attribute node whose name is <a href=
"#doc-xquery-AttributeName">AttributeName</a> if
<code>derives-from(</code><em>AT</em>, <a href=
"#doc-xquery-TypeName">TypeName</a> <code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
attribute node.</p>
<p>Example: <code>attribute(price, currency)</code> matches an
attribute node whose name is <code>price</code> and whose type
annotation is <code>currency</code> (or is derived from
<code>currency</code>).</p>
</li>
<li>
<p><code>attribute(*,</code> <a href=
"#doc-xquery-TypeName">TypeName</a><code>)</code> matches an
attribute node regardless of its name, if
<code>derives-from(</code><em>AT</em>, <a href=
"#doc-xquery-TypeName">TypeName</a><code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
attribute node.</p>
<p>Example: <code>attribute(*, currency)</code> matches any
attribute node whose type annotation is <code>currency</code> (or
is derived from <code>currency</code>), regardless of its name.</p>
</li>
</ol>
</div>
<div class="div4">
<h5><a name="id-schema-attribute-test" id=
"id-schema-attribute-test"></a>2.5.4.6 Schema Attribute Test</h5>
<p>A <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a> matches
an attribute node against a corresponding attribute declaration
found in the <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declarations</a>. It takes the
following form:</p>
<p><code>schema-attribute(</code><a href=
"#doc-xquery-AttributeName">AttributeName</a><code>)</code></p>
<p>If the <a href="#doc-xquery-AttributeName">AttributeName</a>
specified in the <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a> is not
found in the <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declarations</a>, a <a title=
"static error" href="#dt-static-error">static error</a> is raised
[<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>].</p>
<p>A <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a> matches a
candidate attribute node if both of the following conditions are
satisfied:</p>
<ol class="enumar">
<li>
<p>The name of the candidate node matches the specified <a href=
"#doc-xquery-AttributeName">AttributeName</a>.</p>
</li>
<li>
<p><code>derives-from(</code><em>AT, ET</em><code>)</code> is
<code>true</code>, where <em>AT</em> is the type annotation of the
candidate node and <em>ET</em> is the schema type declared for
attribute <a href="#doc-xquery-AttributeName">AttributeName</a> in
the <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declarations</a>.</p>
</li>
</ol>
<p>Example: The <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a>
<code>schema-attribute(color)</code> matches a candidate attribute
node if <code>color</code> is a top-level attribute declaration in
the <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declarations</a>, the name of the
candidate node is <code>color</code>, and the type annotation of
the candidate node is the same as or derived from the schema type
declared for the <code>color</code> attribute.</p>
</div>
</div>
</div>
<div class="div2">
<h3><a name="comments" id="comments"></a>2.6 Comments</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Comment" id=
"doc-xquery-Comment"></a>[151]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Comment">Comment</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"(:" (<a href=
"#doc-xquery-CommentContents">CommentContents</a> | <a href=
"#doc-xquery-Comment">Comment</a>)* ":)"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CommentContents" id=
"doc-xquery-CommentContents"></a>[159]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-CommentContents">CommentContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>+ - (Char* ('(:' |
':)') Char*))</code></td>
</tr>
</tbody>
</table>
<p>Comments may be used to provide informative annotation for
<span class="xquery"><span class="xquery">a query, either in the
<a title="Prolog" href="#dt-prolog">Prolog</a> or in the <a title=
"query body" href="#dt-queryBody">Query Body</a></span></span>.
Comments are lexical constructs only, and do not affect
<span class="xquery"><span class="xquery">query</span></span>
processing.</p>
<p>Comments are strings, delimited by the symbols <code>(:</code>
and <code>:)</code>. Comments may be nested.</p>
<p>A comment may be used anywhere <a title="ignorable whitespace"
href="#IgnorableWhitespace">ignorable whitespace</a> is allowed
(see <a href="#DefaultWhitespaceHandling"><b>A.2.4.1 Default
Whitespace Handling</b></a>).</p>
<p>The following is an example of a comment:</p>
<div class="exampleInner">
<pre>
(: Houston, we have a problem :)
</pre></div>
</div>
</div>
<div class="div1">
<h2><a name="id-expressions" id="id-expressions"></a>3
Expressions</h2>
<p>This section discusses each of the basic kinds of expression.
Each kind of expression has a name such as <code>PathExpr</code>,
which is introduced on the left side of the grammar production that
defines the expression. Since XQuery is a composable language, each
kind of expression is defined in terms of other expressions whose
operators have a higher precedence. In this way, the precedence of
operators is represented explicitly in the grammar.</p>
<p>The order in which expressions are discussed in this document
does not reflect the order of operator precedence. In general, this
document introduces the simplest kinds of expressions first,
followed by more complex expressions. For the complete grammar, see
Appendix [<a href="#nt-bnf"><b>A XQuery Grammar</b></a>].</p>
<p><span class="xquery"><span class="xquery">[<a name="dt-query"
id="dt-query" title="query">Definition</a>: A <b>query</b> consists
of one or more <a title="module" href="#dt-module">modules</a>.] If
a query is executable, one of its modules has a <a title=
"query body" href="#dt-queryBody">Query Body</a> containing an
expression whose value is the result of the query. An expression is
represented in the XQuery grammar by the symbol <a href=
"#doc-xquery-Expr">Expr</a>.</span></span></p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Expr" id=
"doc-xquery-Expr"></a>[31]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Expr">Expr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ExprSingle">ExprSingle</a> (","
<a href="#doc-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ExprSingle" id=
"doc-xquery-ExprSingle"></a>[32]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-FLWORExpr">FLWORExpr</a><br />
| <a href="#doc-xquery-QuantifiedExpr">QuantifiedExpr</a><br />
| <a href="#doc-xquery-TypeswitchExpr">TypeswitchExpr</a><br />
| <a href="#doc-xquery-IfExpr">IfExpr</a><br />
| <a href="#doc-xquery-OrExpr">OrExpr</a></code></td>
</tr>
</tbody>
</table>
<p>The XQuery operator that has lowest precedence is the <a title=
"comma operator" href="#dt-comma-operator">comma operator</a>,
which is used to combine two operands to form a sequence. As shown
in the grammar, a general expression (<a href=
"#doc-xquery-Expr">Expr</a>) can consist of multiple <a href=
"#doc-xquery-ExprSingle">ExprSingle</a> operands, separated by
commas. The name <a href="#doc-xquery-ExprSingle">ExprSingle</a>
denotes an expression that does not contain a top-level <a title=
"comma operator" href="#dt-comma-operator">comma operator</a>
(despite its name, an <a href=
"#doc-xquery-ExprSingle">ExprSingle</a> may evaluate to a sequence
containing more than one item.)</p>
<p>The symbol <a href="#doc-xquery-ExprSingle">ExprSingle</a> is
used in various places in the grammar where an expression is not
allowed to contain a top-level comma. For example, each of the
arguments of a function call must be an <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>, because commas are used to
separate the arguments of a function call.</p>
<p>After the comma, the expressions that have next lowest
precedence are <span class="xquery"><span class="xquery"><a href=
"#doc-xquery-FLWORExpr">FLWORExpr</a>,</span></span> <a href=
"#doc-xquery-QuantifiedExpr">QuantifiedExpr</a>, <span class=
"xquery"><span class="xquery"><a href=
"#doc-xquery-TypeswitchExpr">TypeswitchExpr</a>,</span></span>
<a href="#doc-xquery-IfExpr">IfExpr</a>, and <a href=
"#doc-xquery-OrExpr">OrExpr</a>. Each of these expressions is
described in a separate section of this document.</p>
<div class="div2">
<h3><a name="id-primary-expressions" id=
"id-primary-expressions"></a>3.1 Primary Expressions</h3>
<p>[<a name="dt-primary-expression" id="dt-primary-expression"
title="primary expression">Definition</a>: <b>Primary
expressions</b> are the basic primitives of the language. They
include literals, variable references, context item expressions,
<span class="xquery"><span class=
"xquery">constructors,</span></span> and function calls. A primary
expression may also be created by enclosing any expression in
parentheses, which is sometimes helpful in controlling the
precedence of operators.] <span class="xquery"><span class=
"xquery">Constructors are described in <a href=
"#id-constructors"><b>3.7 Constructors</b></a>.</span></span></p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PrimaryExpr" id=
"doc-xquery-PrimaryExpr"></a>[84]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-PrimaryExpr">PrimaryExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Literal">Literal</a> | <a href=
"#doc-xquery-VarRef">VarRef</a> | <a href=
"#doc-xquery-ParenthesizedExpr">ParenthesizedExpr</a> | <a href=
"#doc-xquery-ContextItemExpr">ContextItemExpr</a> | <a href=
"#doc-xquery-FunctionCall">FunctionCall</a> | <a href=
"#doc-xquery-OrderedExpr">OrderedExpr</a> | <a href=
"#doc-xquery-UnorderedExpr">UnorderedExpr</a> | <a href=
"#doc-xquery-Constructor">Constructor</a></code></td>
</tr>
</tbody>
</table>
<div class="div3">
<h4><a name="id-literals" id="id-literals"></a>3.1.1 Literals</h4>
<p>[<a name="dt-literal" id="dt-literal" title=
"literal">Definition</a>: A <b>literal</b> is a direct syntactic
representation of an atomic value.] XQuery supports two kinds of
literals: numeric literals and string literals.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Literal" id=
"doc-xquery-Literal"></a>[85]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Literal">Literal</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-NumericLiteral">NumericLiteral</a> |
<a href="#doc-xquery-StringLiteral">StringLiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-NumericLiteral" id=
"doc-xquery-NumericLiteral"></a>[86]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-NumericLiteral">NumericLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-IntegerLiteral">IntegerLiteral</a> |
<a href="#doc-xquery-DecimalLiteral">DecimalLiteral</a> | <a href=
"#doc-xquery-DoubleLiteral">DoubleLiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-IntegerLiteral" id=
"doc-xquery-IntegerLiteral"></a>[141]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-IntegerLiteral">IntegerLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Digits">Digits</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DecimalLiteral" id=
"doc-xquery-DecimalLiteral"></a>[142]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DecimalLiteral">DecimalLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("." <a href="#doc-xquery-Digits">Digits</a>) | (<a href=
"#doc-xquery-Digits">Digits</a> "." [0-9]*)</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DoubleLiteral" id=
"doc-xquery-DoubleLiteral"></a>[143]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DoubleLiteral">DoubleLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(("." <a href="#doc-xquery-Digits">Digits</a>) |
(<a href="#doc-xquery-Digits">Digits</a> ("." [0-9]*)?)) [eE] [+-]?
<a href="#doc-xquery-Digits">Digits</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-StringLiteral" id=
"doc-xquery-StringLiteral"></a>[144]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-StringLiteral">StringLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>('"' (<a href=
"#doc-xquery-PredefinedEntityRef">PredefinedEntityRef</a> |
<a href="#prod-xquery-CharRef">CharRef</a> | <a href=
"#doc-xquery-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"') | ("'"
(<a href="#doc-xquery-PredefinedEntityRef">PredefinedEntityRef</a>
| <a href="#prod-xquery-CharRef">CharRef</a> | <a href=
"#doc-xquery-EscapeApos">EscapeApos</a> | [^'&amp;])*
"'")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PredefinedEntityRef" id=
"doc-xquery-PredefinedEntityRef"></a>[145]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-PredefinedEntityRef">PredefinedEntityRef</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos")
";"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Digits" id=
"doc-xquery-Digits"></a>[158]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Digits">Digits</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>[0-9]+</code></td>
</tr>
</tbody>
</table>
<p>The value of a <b>numeric literal</b> containing no
"<code>.</code>" and no <code>e</code> or <code>E</code> character
is an atomic value of type <code>xs:integer</code>. The value of a
numeric literal containing "<code>.</code>" but no <code>e</code>
or <code>E</code> character is an atomic value of type
<code>xs:decimal</code>. The value of a numeric literal containing
an <code>e</code> or <code>E</code> character is an atomic value of
type <code>xs:double</code>. The value of the numeric literal is
determined by casting it to the appropriate type according to the
rules for casting from <code>xs:untypedAtomic</code> to a numeric
type as specified in <a href=
"http://www.w3.org/TR/xpath-functions/#casting-from-strings">Section
17.1.1 Casting from xs:string and
xs:untypedAtomic</a><sup><small>FO</small></sup>.</p>
<p>The value of a <b>string literal</b> is an atomic value whose
type is <code>xs:string</code> and whose value is the string
denoted by the characters between the delimiting apostrophes or
quotation marks. If the literal is delimited by apostrophes, two
adjacent apostrophes within the literal are interpreted as a single
apostrophe. Similarly, if the literal is delimited by quotation
marks, two adjacent quotation marks within the literal are
interpreted as one quotation mark.</p>
<div class="xquery">
<p class="xquery">A string literal may contain a <b>predefined
entity reference</b>. [<a name="dt-predefined-entity-reference" id=
"dt-predefined-entity-reference" title=
"predefined entity reference">Definition</a>: A <b>predefined
entity reference</b> is a short sequence of characters, beginning
with an ampersand, that represents a single character that might
otherwise have syntactic significance.] Each predefined entity
reference is replaced by the character it represents when the
string literal is processed. The predefined entity references
recognized by XQuery are as follows:</p>
</div>
<div class="xquery">
<table width="60%" border="1" class="xquery" summary=
"Special characters">
<tbody>
<tr>
<td align="center">Entity Reference</td>
<td align="center">Character Represented</td>
</tr>
<tr>
<td align="center"><code>&amp;lt;</code></td>
<td align="center"><code>&lt;</code></td>
</tr>
<tr>
<td align="center"><code>&amp;gt;</code></td>
<td align="center"><code>&gt;</code></td>
</tr>
<tr>
<td align="center"><code>&amp;amp;</code></td>
<td align="center"><code>&amp;</code></td>
</tr>
<tr>
<td align="center"><code>&amp;quot;</code></td>
<td align="center"><code>"</code></td>
</tr>
<tr>
<td align="center"><code>&amp;apos;</code></td>
<td align="center"><code>'</code></td>
</tr>
</tbody>
</table>
</div>
<div class="xquery">
<p class="xquery">A string literal may also contain a <b>character
reference</b>. [<a name="dt-character-reference" id=
"dt-character-reference" title=
"character reference">Definition</a>: A <b>character reference</b>
is an XML-style reference to a <a href="#Unicode">[Unicode]</a>
character, identified by its decimal or hexadecimal code point.]
For example, the Euro symbol (€) can be represented by the
character reference <code>&amp;#8364;</code>. Character references
are normatively defined in Section 4.1 of the XML specification (it
is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> whether the
rules in <a href="#XML">[XML 1.0]</a> or <a href="#XML1.1">[XML
1.1]</a> apply.) A <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXQST0090" title=
"err:XQST0090">err:XQST0090</a>] is raised if a character reference
does not identify a valid character in the version of XML that is
in use.</p>
</div>
<p>Here are some examples of literal expressions:</p>
<ul>
<li>
<p><code>"12.5"</code> denotes the string containing the characters
'1', '2', '.', and '5'.</p>
</li>
<li>
<p><code>12</code> denotes the <code>xs:integer</code> value
twelve.</p>
</li>
<li>
<p><code>12.5</code> denotes the <code>xs:decimal</code> value
twelve and one half.</p>
</li>
<li>
<p><code>125E2</code> denotes the <code>xs:double</code> value
twelve thousand, five hundred.</p>
</li>
<li>
<p><code>"He said, ""I don't like it."""</code> denotes a string
containing two quotation marks and one apostrophe.</p>
</li>
<li class="xquery">
<p><code>"Ben &amp;amp; Jerry&amp;apos;s"</code> denotes the
<code>xs:string</code> value "<code>Ben &amp; Jerry's</code>".</p>
</li>
<li class="xquery">
<p><code>"&amp;#8364;99.50"</code> denotes the
<code>xs:string</code> value "<code>€99.50</code>".</p>
</li>
</ul>
<p>The <code>xs:boolean</code> values <code>true</code> and
<code>false</code> can be represented by calls to the <a title=
"built-in function" href="#dt-built-in-function">built-in
functions</a> <code>fn:true()</code> and <code>fn:false()</code>,
respectively.</p>
<p>Values of other atomic types can be constructed by calling the
<a title="constructor function" href=
"#dt-constructor-function">constructor function</a> for the given
type. The constructor functions for XML Schema built-in types are
defined in <a href="#FunctionsAndOperators">[XQuery 1.0 and XPath
2.0 Functions and Operators (Second Edition)]</a>. In general, the
name of a constructor function for a given type is the same as the
name of the type (including its namespace). For example:</p>
<ul>
<li>
<p><code>xs:integer("12")</code> returns the integer value
twelve.</p>
</li>
<li>
<p><code>xs:date("2001-08-25")</code> returns an item whose type is
<code>xs:date</code> and whose value represents the date 25th
August 2001.</p>
</li>
<li>
<p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose
type is <code>xs:dayTimeDuration</code> and whose value represents
a duration of five hours.</p>
</li>
</ul>
<p>Constructor functions can also be used to create special values
that have no literal representation, as in the following
examples:</p>
<ul>
<li>
<p><code>xs:float("NaN")</code> returns the special floating-point
value, "Not a Number."</p>
</li>
<li>
<p><code>xs:double("INF")</code> returns the special
double-precision value, "positive infinity."</p>
</li>
</ul>
<p>It is also possible to construct values of various types by
using a <code>cast</code> expression. For example:</p>
<ul>
<li>
<p><code>9 cast as hatsize</code> returns the atomic value
<code>9</code> whose type is <code>hatsize</code>.</p>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="id-variables" id="id-variables"></a>3.1.2 Variable
References</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-VarRef" id=
"doc-xquery-VarRef"></a>[87]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-VarRef">VarRef</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"$" <a href="#doc-xquery-VarName">VarName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-VarName" id=
"doc-xquery-VarName"></a>[88]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-VarName">VarName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-variable-reference" id="dt-variable-reference"
title="variable reference">Definition</a>: A <b>variable
reference</b> is a QName preceded by a $-sign.] Two variable
references are equivalent if their local names are the same and
their namespace prefixes are bound to the same namespace URI in the
<a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>. An
unprefixed variable reference is in no namespace.</p>
<p>Every variable reference must match a name in the <a title=
"in-scope variables" href="#dt-in-scope-variables">in-scope
variables</a>, which include variables from the following
sources:</p>
<ol class="enumar">
<li class="xquery">
<p>A variable may be declared in a <a title="Prolog" href=
"#dt-prolog">Prolog</a>, in the current <a title="module" href=
"#dt-module">module</a> or an <b>imported module</b>. See <a href=
"#id-query-prolog"><b>4 Modules and Prologs</b></a> for a
discussion of modules and Prologs.</p>
</li>
<li>
<p>The <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> may be augmented by
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>
variables.</p>
</li>
<li>
<p>A variable may be bound by an XQuery expression. <span class=
"xquery"><span class="xquery">The kinds of expressions that can
bind variables are FLWOR expressions (<a href=
"#id-flwor-expressions"><b>3.8 FLWOR Expressions</b></a>),
quantified expressions (<a href=
"#id-quantified-expressions"><b>3.11 Quantified
Expressions</b></a>), and <code>typeswitch</code> expressions
(<a href="#id-typeswitch"><b>3.12.2 Typeswitch</b></a>). Function
calls also bind values to the formal parameters of functions before
executing the function body.</span></span></p>
</li>
</ol>
<p>Every variable binding has a static scope. The scope defines
where references to the variable can validly occur. It is a
<a title="static error" href="#dt-static-error">static error</a>
[<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to
reference a variable that is not in scope. If a variable is bound
in the <a title="static context" href="#dt-static-context">static
context</a> for an expression, that variable is in scope for the
entire expression.</p>
<div class="xquery">
<p class="xquery">A reference to a variable that was declared
<code>external</code>, but was not bound to a value by the external
environment, raises a dynamic error [<a href="#ERRXPDY0002" title=
"err:XPDY0002">err:XPDY0002</a>].</p>
</div>
<p>If a variable reference matches two or more variable bindings
that are in scope, then the reference is taken as referring to the
inner binding, that is, the one whose scope is smaller. At
evaluation time, the value of a variable reference is the value of
the expression to which the relevant variable is bound. The scope
of a variable binding is defined separately for each kind of
expression that can bind variables.</p>
</div>
<div class="div3">
<h4><a name="id-paren-expressions" id=
"id-paren-expressions"></a>3.1.3 Parenthesized Expressions</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ParenthesizedExpr" id=
"doc-xquery-ParenthesizedExpr"></a>[89]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ParenthesizedExpr">ParenthesizedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"(" <a href="#doc-xquery-Expr">Expr</a>? ")"</code></td>
</tr>
</tbody>
</table>
<p>Parentheses may be used to enforce a particular evaluation order
in expressions that contain multiple operators. For example, the
expression <code>(2 + 4) * 5</code> evaluates to thirty, since the
parenthesized expression <code>(2 + 4)</code> is evaluated first
and its result is multiplied by five. Without parentheses, the
expression <code>2 + 4 * 5</code> evaluates to twenty-two, because
the multiplication operator has higher precedence than the addition
operator.</p>
<p>Empty parentheses are used to denote an empty sequence, as
described in <a href="#construct_seq"><b>3.3.1 Constructing
Sequences</b></a>.</p>
</div>
<div class="div3">
<h4><a name="id-context-item-expression" id=
"id-context-item-expression"></a>3.1.4 Context Item Expression</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ContextItemExpr" id=
"doc-xquery-ContextItemExpr"></a>[90]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ContextItemExpr">ContextItemExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"."</code></td>
</tr>
</tbody>
</table>
<p>A <b>context item expression</b> evaluates to the <a title=
"context item" href="#dt-context-item">context item</a>, which may
be either a node (as in the expression
<code>fn:doc("bib.xml")/books/book[fn:count(./author)&gt;1]</code>)
or an atomic value (as in the expression <code>(1 to 100)[. mod 5
eq 0]</code>).</p>
<p>If the <a title="context item" href="#dt-context-item">context
item</a> is <a title="undefined" href=
"#dt-undefined">undefined</a>, a context item expression raises a
dynamic error [<a href="#ERRXPDY0002" title=
"err:XPDY0002">err:XPDY0002</a>].</p>
</div>
<div class="div3">
<h4><a name="id-function-calls" id="id-function-calls"></a>3.1.5
Function Calls</h4>
<p>[<a name="dt-built-in-function" id="dt-built-in-function" title=
"built-in function">Definition</a>: The <b>built-in functions</b>
supported by XQuery are defined in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.] <span class="xquery"><span class=
"xquery">Additional functions may be declared in a <a title=
"Prolog" href="#dt-prolog">Prolog</a>, imported from a <a title=
"library module" href="#dt-library-module">library module</a>, or
provided by the external environment as part of the <a title=
"static context" href="#dt-static-context">static
context</a>.</span></span></p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-FunctionCall" id=
"doc-xquery-FunctionCall"></a>[93]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-FunctionCall">FunctionCall</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a> "(" (<a href=
"#doc-xquery-ExprSingle">ExprSingle</a> ("," <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>)*)? ")"</code></td>
</tr>
</tbody>
</table>
<p>A <b>function call</b> consists of a QName followed by a
parenthesized list of zero or more expressions, called
<b>arguments</b>. If the QName in the function call has no
namespace prefix, it is considered to be in the <a title=
"default function namespace" href="#dt-def-fn-ns">default function
namespace.</a></p>
<p>If the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> and number of arguments in
a function call do not match the name and arity of a <a title=
"function signature" href="#dt-function-signature">function
signature</a> in the <a title="static context" href=
"#dt-static-context">static context</a>, a <a title="static error"
href="#dt-static-error">static error</a> is raised [<a href=
"#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p>
<p>A function call is evaluated as follows:</p>
<ol class="enumar">
<li>
<p>Argument expressions are evaluated, producing argument values.
The order of argument evaluation is <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> and a
function need not evaluate an argument if the function can evaluate
its body without evaluating that argument.</p>
</li>
<li>
<p>Each argument value is converted by applying the function
conversion rules listed below.</p>
</li>
<li class="xquery">
<p>If the function is a built-in function, it is evaluated using
the converted argument values. The result is either an instance of
the function's declared return type or a dynamic error. Errors
raised by built-in functions are defined in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
</li>
<li class="xquery">
<p>If the function is a user-declared function that has a body, the
converted argument values are bound to the formal parameters of the
function, and the function body is evaluated. The value returned by
the function body is then converted to the declared return type of
the function by applying the function conversion rules.</p>
<p>When a converted argument value is bound to a function
parameter, the argument value retains its most specific <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a>, even
though this type may be derived from the type of the formal
parameter. For example, a function with a parameter <code>$p</code>
of type <code>xs:decimal</code> can be invoked with an argument of
type <code>xs:integer</code>, which is derived from
<code>xs:decimal</code>. During the processing of this function
invocation, the <a title="dynamic type" href=
"#dt-dynamic-type">dynamic type</a> of <code>$p</code> inside the
body of the function is considered to be <code>xs:integer</code>.
Similarly, the value returned by a function retains its most
specific type, which may be derived from the declared return type
of the function. For example, a function that has a declared return
type of <code>xs:decimal</code> may in fact return a value of
dynamic type <code>xs:integer</code>.</p>
<p>During evaluation of a function body, the <a title=
"static context" href="#dt-static-context">static context</a> and
<a title="dynamic context" href="#dt-dynamic-context">dynamic
context</a> for expression evaluation are defined by the <a title=
"module" href="#dt-module">module</a> in which the function is
declared, which is not necessarily the same as the <a title=
"module" href="#dt-module">module</a> in which the function is
called. For example, the variables in scope while evaluating a
function body are defined by in-scope variables of the module that
declares the function rather than the module in which the function
is called. During evaluation of a function body, the <a title=
"focus" href="#dt-focus">focus</a> (context item, context position,
and context size) is <a title="undefined" href=
"#dt-undefined">undefined</a>, except where it is defined by some
expression inside the function body.</p>
</li>
<li class="xquery">
<p>If the function is a user-declared external function, its
<a title="function implementation" href=
"#dt-function-implementation">function implementation</a> is
invoked with the converted argument values. The result is either a
value of the declared type or an <a title="implementation defined"
href="#dt-implementation-defined">implementation-defined</a> error
(see <a href="#id-consistency-constraints"><b>2.2.5 Consistency
Constraints</b></a>).</p>
</li>
</ol>
<p>The <b>function conversion rules</b> are used to convert an
argument value <span class="xquery"><span class="xquery">or a
return value</span></span> to its expected type; that is, to the
declared type of the function <span class="xquery"><span class=
"xquery">parameter or return.</span></span> The expected type is
expressed as a <a title="sequence type" href=
"#dt-sequence-type">sequence type</a>. The function conversion
rules are applied to a given value as follows:</p>
<ul>
<li>
<p>If the expected type is a sequence of an atomic type (possibly
with an occurrence indicator <code>*</code>, <code>+</code>, or
<code>?</code>), the following conversions are applied:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the given value, resulting in a sequence of atomic
values.</p>
</li>
<li>
<p>Each item in the atomic sequence that is of type
<code>xs:untypedAtomic</code> is cast to the expected atomic type.
For <a title="built-in function" href=
"#dt-built-in-function">built-in functions</a> where the expected
type is specified as <a title="numeric" href=
"#dt-numeric">numeric</a>, arguments of type
<code>xs:untypedAtomic</code> are cast to
<code>xs:double</code>.</p>
</li>
<li>
<p>For each <a title="numeric" href="#dt-numeric">numeric</a> item
in the atomic sequence that can be <a title="type promotion" href=
"#dt-type-promotion">promoted</a> to the expected atomic type using
numeric promotion as described in <a href="#promotion"><b>B.1 Type
Promotion</b></a>, the promotion is done.</p>
</li>
<li>
<p>For each item of type <code>xs:anyURI</code> in the atomic
sequence that can be <a title="type promotion" href=
"#dt-type-promotion">promoted</a> to the expected atomic type using
URI promotion as described in <a href="#promotion"><b>B.1 Type
Promotion</b></a>, the promotion is done.</p>
</li>
</ol>
</li>
<li>
<p>If, after the above conversions, the resulting value does not
match the expected type according to the rules for <a title=
"SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType Matching</a>, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].
<span class="xquery"><span class="xquery">If the function call
takes place in a <a title="module" href="#dt-module">module</a>
other than the <a title="module" href="#dt-module">module</a> in
which the function is defined, this rule must be satisfied in both
the module where the function is called and the module where the
function is defined (the test is repeated because the two modules
may have different <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a>.)</span></span> Note
that the rules for <a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType Matching</a> permit a
value of a derived type to be substituted for a value of its base
type.</p>
</li>
</ul>
<p>Since the arguments of a function call are separated by commas,
any argument expression that contains a top-level <a title=
"comma operator" href="#dt-comma-operator">comma operator</a> must
be enclosed in parentheses. Here are some illustrative examples of
function calls:</p>
<ul>
<li>
<p><code>my:three-argument-function(1, 2, 3)</code> denotes a
function call with three arguments.</p>
</li>
<li>
<p><code>my:two-argument-function((1, 2), 3)</code> denotes a
function call with two arguments, the first of which is a sequence
of two values.</p>
</li>
<li>
<p><code>my:two-argument-function(1, ())</code> denotes a function
call with two arguments, the second of which is an empty
sequence.</p>
</li>
<li>
<p><code>my:one-argument-function((1, 2, 3))</code> denotes a
function call with one argument that is a sequence of three
values.</p>
</li>
<li>
<p><code>my:one-argument-function(( ))</code> denotes a function
call with one argument that is an empty sequence.</p>
</li>
<li>
<p><code>my:zero-argument-function( )</code> denotes a function
call with zero arguments.</p>
</li>
</ul>
</div>
</div>
<div class="div2">
<h3><a name="id-path-expressions" id="id-path-expressions"></a>3.2
Path Expressions</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PathExpr" id=
"doc-xquery-PathExpr"></a>[68]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-PathExpr">PathExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("/" <a href=
"#doc-xquery-RelativePathExpr">RelativePathExpr</a>?)<br />
| ("//" <a href=
"#doc-xquery-RelativePathExpr">RelativePathExpr</a>)<br />
| <a href=
"#doc-xquery-RelativePathExpr">RelativePathExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-RelativePathExpr" id=
"doc-xquery-RelativePathExpr"></a>[69]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-RelativePathExpr">RelativePathExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-StepExpr">StepExpr</a> (("/" | "//")
<a href="#doc-xquery-StepExpr">StepExpr</a>)*</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-path-expression" id="dt-path-expression" title=
"path expression">Definition</a>: A <b>path expression</b> can be
used to locate nodes within trees. A path expression consists of a
series of one or more <a title="step" href="#dt-step">steps</a>,
separated by "<code>/</code>" or "<code>//</code>", and optionally
beginning with "<code>/</code>" or "<code>//</code>".] An initial
"<code>/</code>" or "<code>//</code>" is an abbreviation for one or
more initial steps that are implicitly added to the beginning of
the path expression, as described below.</p>
<p>A path expression consisting of a single step is evaluated as
described in <a href="#id-steps"><b>3.2.1 Steps</b></a>.</p>
<p>A "<code>/</code>" at the beginning of a path expression is an
abbreviation for the initial step
<code><span>(fn:root(self::node()) treat as
document-node())</span>/</code> (however, if the "<code>/</code>"
is the entire path expression, the trailing "<code>/</code>" is
omitted from the expansion.) The effect of this initial step is to
begin the path at the root node of the tree that contains the
context node. If the context item is not a node, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0020" title="err:XPTY0020">err:XPTY0020</a>]. At
evaluation time, if the root node above the context node is not a
document node, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXPDY0050" title="err:XPDY0050">err:XPDY0050</a>].</p>
<p>A "<code>//</code>" at the beginning of a path expression is an
abbreviation for the initial steps
<code><span>(fn:root(self::node()) treat as
document-node())</span>/descendant-or-self::node()/</code>
(however, "<code>//</code>" by itself is not a valid path
expression [<a href="#ERRXPST0003" title=
"err:XPST0003">err:XPST0003</a>].) The effect of these initial
steps is to establish an initial node sequence that contains the
root of the tree in which the context node is found, plus all nodes
descended from this root. This node sequence is used as the input
to subsequent steps in the path expression. If the context item is
not a node, a <a title="type error" href="#dt-type-error">type
error</a> is raised [<a href="#ERRXPTY0020" title=
"err:XPTY0020">err:XPTY0020</a>]. At evaluation time, if the root
node above the context node is not a document node, a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a> is
raised [<a href="#ERRXPDY0050" title=
"err:XPDY0050">err:XPDY0050</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The descendants of a node do not include attribute nodes .</p>
</div>
<p>Each non-initial occurrence of "<code>//</code>" in a path
expression is expanded as described in <a href="#abbrev"><b>3.2.4
Abbreviated Syntax</b></a>, leaving a sequence of steps separated
by "<code>/</code>". This sequence of steps is then evaluated from
left to right. Each operation <code>E1/E2</code> is evaluated as
follows: Expression <code>E1</code> is evaluated, and if the result
is not a (possibly empty) sequence of nodes, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0019" title="err:XPTY0019">err:XPTY0019</a>].
Each node resulting from the evaluation of <code>E1</code> then
serves in turn to provide an <b>inner focus</b> for an evaluation
of <code>E2</code>, as described in <a href=
"#eval_context"><b>2.1.2 Dynamic Context</b></a>. The sequences
resulting from all the evaluations of <code>E2</code> are combined
as follows:</p>
<ol class="enumar">
<li>
<p>If every evaluation of <code>E2</code> returns a (possibly
empty) sequence of nodes, these sequences are combined, and
duplicate nodes are eliminated based on node identity. <span class=
"xquery"><span class="xquery">If <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is <code>ordered</code>, the
resulting node sequence is returned in <a title="document order"
href="#dt-document-order">document order</a>; otherwise it is
returned in <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
order.</span></span></p>
</li>
<li>
<p>If every evaluation of <code>E2</code> returns a (possibly
empty) sequence of atomic values, these sequences are concatenated
and returned. <span class="xquery"><span class="xquery">If
<a title="ordering mode" href="#dt-ordering-mode">ordering mode</a>
is <code>ordered</code>, the returned sequence preserves the
orderings within and among the subsequences generated by the
evaluations of <code>E2</code>; otherwise the order of the returned
sequence is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</span></span></p>
</li>
<li>
<p>If the multiple evaluations of <code>E2</code> return at least
one node and at least one atomic value, a <a title="type error"
href="#dt-type-error">type error</a> is raised [<a href=
"#ERRXPTY0018" title="err:XPTY0018">err:XPTY0018</a>].</p>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Since each step in a path provides context nodes for the
following step, in effect, only the last step in a path is allowed
to return a sequence of atomic values.</p>
</div>
<p>As an example of a path expression,
<code>child::div1/child::para</code> selects the <code>para</code>
element children of the <code>div1</code> element children of the
context node, or, in other words, the <code>para</code> element
grandchildren of the context node that have <code>div1</code>
parents.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p id="Chg-slash-note">The "<code>/</code>" character can be used
either as a complete path expression or as the beginning of a
longer path expression such as "<code>/*</code>". Also,
"<code>*</code>" is both the multiply operator and a wildcard in
path expressions. This can cause parsing difficulties when
"<code>/</code>" appears on the left hand side of "<code>*</code>".
This is resolved using the <a href=
"#parse-note-leading-lone-slash">leading-lone-slash</a> constraint.
For example, "<code>/*</code>" and "<code>/ *</code>" are valid
path expressions containing wildcards, but "<code>/*5</code>" and
"<code>/ * 5</code>" raise syntax errors. Parentheses must be used
when "<code>/</code>" is used on the left hand side of an operator,
as in "<code>(/) * 5</code>". Similarly, "<code>4 + / * 5</code>"
raises a syntax error, but "<code>4 + (/) * 5</code>" is a valid
expression. The expression "<code>4 + /</code>" is also valid,
because <code>/</code> does not occur on the left hand side of the
operator.</p>
</div>
<div class="div3">
<h4><a name="id-steps" id="id-steps"></a>3.2.1 Steps</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-StepExpr" id=
"doc-xquery-StepExpr"></a>[70]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-StepExpr">StepExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-FilterExpr">FilterExpr</a> |
<a href="#doc-xquery-AxisStep">AxisStep</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AxisStep" id=
"doc-xquery-AxisStep"></a>[71]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AxisStep">AxisStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#doc-xquery-ReverseStep">ReverseStep</a> |
<a href="#doc-xquery-ForwardStep">ForwardStep</a>) <a href=
"#doc-xquery-PredicateList">PredicateList</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ForwardStep" id=
"doc-xquery-ForwardStep"></a>[72]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ForwardStep">ForwardStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#doc-xquery-ForwardAxis">ForwardAxis</a>
<a href="#doc-xquery-NodeTest">NodeTest</a>) | <a href=
"#doc-xquery-AbbrevForwardStep">AbbrevForwardStep</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ReverseStep" id=
"doc-xquery-ReverseStep"></a>[75]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ReverseStep">ReverseStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#doc-xquery-ReverseAxis">ReverseAxis</a>
<a href="#doc-xquery-NodeTest">NodeTest</a>) | <a href=
"#doc-xquery-AbbrevReverseStep">AbbrevReverseStep</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PredicateList" id=
"doc-xquery-PredicateList"></a>[82]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-PredicateList">PredicateList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-Predicate">Predicate</a>*</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-step" id="dt-step" title="step">Definition</a>: A
<b>step</b> is a part of a <a title="path expression" href=
"#dt-path-expression">path expression</a> that generates a sequence
of items and then filters the sequence by zero or more <a title=
"predicate" href="#dt-predicate">predicates</a>. The value of the
step consists of those items that satisfy the predicates, working
from left to right. A step may be either an <a title="axis step"
href="#dt-axis-step">axis step</a> or a <a title=
"filter expression" href="#dt-filter-expression">filter
expression</a>.] Filter expressions are described in <a href=
"#id-filter-expr"><b>3.3.2 Filter Expressions</b></a>.</p>
<p>[<a name="dt-axis-step" id="dt-axis-step" title=
"axis step">Definition</a>: An <b>axis step</b> returns a sequence
of nodes that are reachable from the context node via a specified
axis. Such a step has two parts: an <b>axis</b>, which defines the
"direction of movement" for the step, and a <a title="node test"
href="#dt-node-test">node test</a>, which selects nodes based on
their kind, name, and/or <a title="type annotation" href=
"#dt-type-annotation">type annotation</a>.] If the context item is
a node, an axis step returns a sequence of zero or more nodes;
otherwise, a <a title="type error" href="#dt-type-error">type
error</a> is raised [<a href="#ERRXPTY0020" title=
"err:XPTY0020">err:XPTY0020</a>]. <span class="xquery"><span class=
"xquery">If <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is <code>ordered</code>, the
resulting node sequence is returned in <a title="document order"
href="#dt-document-order">document order</a>; otherwise it is
returned in <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
order.</span></span> An axis step may be either a <b>forward
step</b> or a <b>reverse step</b>, followed by zero or more
<a title="predicate" href="#dt-predicate">predicates</a>.</p>
<p>In the <b>abbreviated syntax</b> for a step, the axis can be
omitted and other shorthand notations can be used as described in
<a href="#abbrev"><b>3.2.4 Abbreviated Syntax</b></a>.</p>
<p>The unabbreviated syntax for an axis step consists of the axis
name and node test separated by a double colon. The result of the
step consists of the nodes reachable from the context node via the
specified axis that have the node kind, name, and/or <a title=
"type annotation" href="#dt-type-annotation">type annotation</a>
specified by the node test. For example, the step
<code>child::para</code> selects the <code>para</code> element
children of the context node: <code>child</code> is the name of the
axis, and <code>para</code> is the name of the element nodes to be
selected on this axis. The available axes are described in <a href=
"#axes"><b>3.2.1.1 Axes</b></a>. The available node tests are
described in <a href="#node-tests"><b>3.2.1.2 Node Tests</b></a>.
Examples of steps are provided in <a href="#unabbrev"><b>3.2.3
Unabbreviated Syntax</b></a> and <a href="#abbrev"><b>3.2.4
Abbreviated Syntax</b></a>.</p>
<div class="div4">
<h5><a name="axes" id="axes"></a>3.2.1.1 Axes</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ForwardAxis" id=
"doc-xquery-ForwardAxis"></a>[73]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ForwardAxis">ForwardAxis</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("child" "::")<br />
| ("descendant" "::")<br />
| ("attribute" "::")<br />
| ("self" "::")<br />
| ("descendant-or-self" "::")<br />
| ("following-sibling" "::")<br />
| ("following" "::")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ReverseAxis" id=
"doc-xquery-ReverseAxis"></a>[76]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ReverseAxis">ReverseAxis</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("parent" "::")<br />
| ("ancestor" "::")<br />
| ("preceding-sibling" "::")<br />
| ("preceding" "::")<br />
| ("ancestor-or-self" "::")</code></td>
</tr>
</tbody>
</table>
<div class="xquery">
<p class="xquery">XQuery supports the following axes (subject to
limitations as described in <a href=
"#id-full-axis-feature"><b>5.2.4 Full Axis Feature</b></a>):</p>
</div>
<ul>
<li>
<p>The <code>child</code> axis contains the children of the context
node, which are the nodes returned by the <code>dm:children</code>
accessor in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data
Model (Second Edition)]</a>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Only document nodes and element nodes have children. If the
context node is any other kind of node, or if the context node is
an empty document or element node, then the child axis is an empty
sequence. The children of a document node or element node may be
element, processing instruction, comment, or text nodes. Attribute
and document nodes can never appear as children.</p>
</div>
</li>
<li>
<p>the <code>descendant</code> axis is defined as the transitive
closure of the child axis; it contains the descendants of the
context node (the children, the children of the children, and so
on)</p>
</li>
<li>
<p>the <code>parent</code> axis contains the sequence returned by
the <code>dm:parent</code> accessor in <a href="#datamodel">[XQuery
1.0 and XPath 2.0 Data Model (Second Edition)]</a>, which returns
the parent of the context node, or an empty sequence if the context
node has no parent</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>An attribute node may have an element node as its parent, even
though the attribute node is not a child of the element node.</p>
</div>
</li>
<li>
<p>the <code>ancestor</code> axis is defined as the transitive
closure of the parent axis; it contains the ancestors of the
context node (the parent, the parent of the parent, and so on)</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The ancestor axis includes the root node of the tree in which
the context node is found, unless the context node is the root
node.</p>
</div>
</li>
<li>
<p>the <code>following-sibling</code> axis contains the context
node's following siblings, those children of the context node's
parent that occur after the context node in <a title=
"document order" href="#dt-document-order">document order</a>; if
the context node is an attribute node, the
<code>following-sibling</code> axis is empty</p>
</li>
<li>
<p>the <code>preceding-sibling</code> axis contains the context
node's preceding siblings, those children of the context node's
parent that occur before the context node in <a title=
"document order" href="#dt-document-order">document order</a>; if
the context node is an attribute node, the
<code>preceding-sibling</code> axis is empty</p>
</li>
<li>
<p>the <code>following</code> axis contains all nodes that are
descendants of the root of the tree in which the context node is
found, are not descendants of the context node, and occur after the
context node in <a title="document order" href=
"#dt-document-order">document order</a></p>
</li>
<li>
<p>the <code>preceding</code> axis contains all nodes that are
descendants of the root of the tree in which the context node is
found, are not ancestors of the context node, and occur before the
context node in <a title="document order" href=
"#dt-document-order">document order</a></p>
</li>
<li>
<p>the <code>attribute</code> axis contains the attributes of the
context node, which are the nodes returned by the
<code>dm:attributes</code> accessor in <a href="#datamodel">[XQuery
1.0 and XPath 2.0 Data Model (Second Edition)]</a>; the axis will
be empty unless the context node is an element</p>
</li>
<li>
<p>the <code>self</code> axis contains just the context node
itself</p>
</li>
<li>
<p>the <code>descendant-or-self</code> axis contains the context
node and the descendants of the context node</p>
</li>
<li>
<p>the <code>ancestor-or-self</code> axis contains the context node
and the ancestors of the context node; thus, the ancestor-or-self
axis will always include the root node</p>
</li>
</ul>
<p>Axes can be categorized as <b>forward axes</b> and <b>reverse
axes</b>. An axis that only ever contains the context node or nodes
that are after the context node in <a title="document order" href=
"#dt-document-order">document order</a> is a forward axis. An axis
that only ever contains the context node or nodes that are before
the context node in <a title="document order" href=
"#dt-document-order">document order</a> is a reverse axis.</p>
<p>The <code>parent</code>, <code>ancestor</code>,
<code>ancestor-or-self</code>, <code>preceding</code>, and
<code>preceding-sibling</code> axes are reverse axes; all other
axes are forward axes. The <code>ancestor</code>,
<code>descendant</code>, <code>following</code>,
<code>preceding</code> and <code>self</code> axes partition a
document (ignoring attribute nodes): they do not overlap and
together they contain all the nodes in the document.</p>
<p>[<a name="dt-principal-node-kind" id="dt-principal-node-kind"
title="principal node kind">Definition</a>: Every axis has a
<b>principal node kind</b>. If an axis can contain elements, then
the principal node kind is element; otherwise, it is the kind of
nodes that the axis can contain.] Thus:</p>
<ul>
<li>
<p>For the attribute axis, the principal node kind is
attribute.</p>
</li>
<li>
<p>For all other axes, the principal node kind is element.</p>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="node-tests" id="node-tests"></a>3.2.1.2 Node
Tests</h5>
<p>[<a name="dt-node-test" id="dt-node-test" title=
"node test">Definition</a>: A <b>node test</b> is a condition that
must be true for each node selected by a <a title="step" href=
"#dt-step">step</a>.] The condition may be based on the kind of the
node (element, attribute, text, document, comment, or processing
instruction), the name of the node, or (in the case of element,
attribute, and document nodes), the <a title="type annotation"
href="#dt-type-annotation">type annotation</a> of the node.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-NodeTest" id=
"doc-xquery-NodeTest"></a>[78]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-NodeTest">NodeTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-KindTest">KindTest</a> | <a href=
"#doc-xquery-NameTest">NameTest</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-NameTest" id=
"doc-xquery-NameTest"></a>[79]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-NameTest">NameTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a> | <a href=
"#doc-xquery-Wildcard">Wildcard</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Wildcard" id=
"doc-xquery-Wildcard"></a>[80]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Wildcard">Wildcard</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"*"<br />
| (<a href="#prod-xquery-NCName">NCName</a> ":" "*")<br />
| ("*" ":" <a href="#prod-xquery-NCName">NCName</a>)</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-name-test" id="dt-name-test" title=
"name test">Definition</a>: A node test that consists only of a
QName or a Wildcard is called a <b>name test</b>.] A name test is
true if and only if the <b>kind</b> of the node is the <a title=
"principal node kind" href="#dt-principal-node-kind">principal node
kind</a> for the step axis and the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> of the node is equal (as
defined by the <code>eq</code> operator) to the <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a>
specified by the name test. For example, <code>child::para</code>
selects the <code>para</code> element children of the context node;
if the context node has no <code>para</code> children, it selects
an empty set of nodes. <code>attribute::abc:href</code> selects the
attribute of the context node with the QName <code>abc:href</code>;
if the context node has no such attribute, it selects an empty set
of nodes.</p>
<p>A QName in a name test is resolved into an <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a> using
the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> in the
expression context. It is a <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXPST0081" title=
"err:XPST0081">err:XPST0081</a>] if the QName has a prefix that
does not correspond to any statically known namespace. An
unprefixed QName, when used as a name test on an axis whose
<a title="principal node kind" href=
"#dt-principal-node-kind">principal node kind</a> is element, has
the namespace URI of the <a title="default element/type namespace"
href="#dt-def-elemtype-ns">default element/type namespace</a> in
the expression context; otherwise, it has no namespace URI.</p>
<p>A name test is not satisfied by an element node whose name does
not match the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> of the name test, even if
it is in a <a title="substitution group" href=
"#dt-substitution-group">substitution group</a> whose head is the
named element.</p>
<p>A node test <code>*</code> is true for any node of the <a title=
"principal node kind" href="#dt-principal-node-kind">principal node
kind</a> of the step axis. For example, <code>child::*</code> will
select all element children of the context node, and
<code>attribute::*</code> will select all attributes of the context
node.</p>
<p>A node test can have the form <code>NCName:*</code>. In this
case, the prefix is expanded in the same way as with a QName, using
the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> in the
<a title="static context" href="#dt-static-context">static
context</a>. If the prefix is not found in the statically known
namespaces, a <a title="static error" href=
"#dt-static-error">static error</a> is raised [<a href=
"#ERRXPST0081" title="err:XPST0081">err:XPST0081</a>]. The node
test is true for any node of the <a title="principal node kind"
href="#dt-principal-node-kind">principal node kind</a> of the step
axis whose <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> has the namespace URI to
which the prefix is bound, regardless of the local part of the
name.</p>
<p>A node test can also have the form <code>*:NCName</code>. In
this case, the node test is true for any node of the <a title=
"principal node kind" href="#dt-principal-node-kind">principal node
kind</a> of the step axis whose local name matches the given
NCName, regardless of its namespace or lack of a namespace.</p>
<p>[<a name="dt-kind-test" id="dt-kind-test" title=
"kind test">Definition</a>: An alternative form of a node test
called a <b>kind test</b> can select nodes based on their kind,
name, and <a title="type annotation" href=
"#dt-type-annotation">type annotation</a>.] The syntax and
semantics of a kind test are described in <a href=
"#id-sequencetype-syntax"><b>2.5.3 SequenceType Syntax</b></a> and
<a href="#id-sequencetype-matching"><b>2.5.4 SequenceType
Matching</b></a>. When a kind test is used in a <a title=
"node test" href="#dt-node-test">node test</a>, only those nodes on
the designated axis that match the kind test are selected. Shown
below are several examples of kind tests that might be used in path
expressions:</p>
<ul>
<li>
<p><code>node()</code> matches any node.</p>
</li>
<li>
<p><code>text()</code> matches any text node.</p>
</li>
<li>
<p><code>comment()</code> matches any comment node.</p>
</li>
<li>
<p><code>element()</code> matches any element node.</p>
</li>
<li>
<p><code>schema-element(person)</code> matches any element node
whose name is <code>person</code> (or is in the <a title=
"substitution group" href="#dt-substitution-group">substitution
group</a> headed by <code>person</code>), and whose type annotation
is the same as (or is derived from) the declared type of the
<code>person</code> element in the <a title=
"in-scope element declarations" href="#dt-is-elems">in-scope
element declarations</a>.</p>
</li>
<li>
<p><code>element(person)</code> matches any element node whose name
is <code>person</code>, regardless of its type annotation.</p>
</li>
<li>
<p><code>element(person, surgeon)</code> matches any non-nilled
element node whose name is <code>person</code>, and whose type
annotation is <code>surgeon</code> or is derived from
<code>surgeon</code>.</p>
</li>
<li>
<p><code>element(*, surgeon)</code> matches any non-nilled element
node whose type annotation is <code>surgeon</code> (or is derived
from <code>surgeon</code>), regardless of its name.</p>
</li>
<li>
<p><code>attribute()</code> matches any attribute node.</p>
</li>
<li>
<p><code>attribute(price)</code> matches any attribute whose name
is <code>price</code>, regardless of its type annotation.</p>
</li>
<li>
<p><code>attribute(*, xs:decimal)</code> matches any attribute
whose type annotation is <code>xs:decimal</code> (or is derived
from <code>xs:decimal</code>), regardless of its name.</p>
</li>
<li>
<p><code>document-node()</code> matches any document node.</p>
</li>
<li>
<p><code>document-node(element(book))</code> matches any document
node whose content consists of a single element node that satisfies
the <a title="kind test" href="#dt-kind-test">kind test</a>
<code>element(book)</code>, interleaved with zero or more comments
and processing instructions.</p>
</li>
</ul>
</div>
</div>
<div class="div3">
<h4><a name="id-predicates" id="id-predicates"></a>3.2.2
Predicates</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Predicate" id=
"doc-xquery-Predicate"></a>[83]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-Predicate">Predicate</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"[" <a href="#doc-xquery-Expr">Expr</a> "]"</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-predicate" id="dt-predicate" title=
"predicate">Definition</a>: A <b>predicate</b> consists of an
expression, called a <b>predicate expression</b>, enclosed in
square brackets. A predicate serves to filter a sequence, retaining
some items and discarding others.] In the case of multiple adjacent
predicates, the predicates are applied from left to right, and the
result of applying each predicate serves as the input sequence for
the following predicate.</p>
<p>For each item in the input sequence, the predicate expression is
evaluated using an <b>inner focus</b>, defined as follows: The
context item is the item currently being tested against the
predicate. The context size is the number of items in the input
sequence. The context position is the position of the context item
within the input sequence. For the purpose of evaluating the
context position within a predicate, the input sequence is
considered to be sorted as follows: into document order if the
predicate is in a forward-axis step, into reverse document order if
the predicate is in a reverse-axis step, or in its original order
if the predicate is not in a step.</p>
<p>For each item in the input sequence, the result of the predicate
expression is coerced to an <code>xs:boolean</code> value, called
the <b>predicate truth value</b>, as described below. Those items
for which the predicate truth value is <code>true</code> are
retained, and those for which the predicate truth value is
<code>false</code> are discarded.</p>
<p>The predicate truth value is derived by applying the following
rules, in order:</p>
<ol class="enumar">
<li>
<p>If the value of the predicate expression is a <a title=
"singleton" href="#dt-singleton">singleton</a> atomic value of a
<a title="numeric" href="#dt-numeric">numeric</a> type or derived
from a <a title="numeric" href="#dt-numeric">numeric</a> type, the
predicate truth value is <code>true</code> if the value of the
predicate expression is equal (by the <code>eq</code> operator) to
the <b>context position</b>, and is <code>false</code> otherwise.
[<a name="dt-numeric-predicate" id="dt-numeric-predicate" title=
"numeric predicate">Definition</a>: A predicate whose predicate
expression returns a numeric type is called a <b>numeric
predicate</b>.]</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>In a region of a query where <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is <code>unordered</code>,
the result of a numeric predicate is nondeterministic, as explained
in <a href="#id-unordered-expressions"><b>3.9 Ordered and Unordered
Expressions</b></a>.</p>
</div>
</li>
<li>
<p>Otherwise, the predicate truth value is the <a title=
"effective boolean value" href="#dt-ebv">effective boolean
value</a> of the predicate expression.</p>
</li>
</ol>
<p>Here are some examples of <a title="axis step" href=
"#dt-axis-step">axis steps</a> that contain predicates:</p>
<ul>
<li>
<p>This example selects the second <code>chapter</code> element
that is a child of the context node:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
child::chapter[2]
</pre></div>
</div>
</li>
<li>
<p>This example selects all the descendants of the context node
that are elements named <code>"toy"</code> and whose
<code>color</code> attribute has the value <code>"red"</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
descendant::toy[attribute::color = "red"]
</pre></div>
</div>
</li>
<li>
<p>This example selects all the <code>employee</code> children of
the context node that have both a <code>secretary</code> child
element and an <code>assistant</code> child element:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
child::employee[secretary][assistant]
</pre></div>
</div>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>When using <a title="predicate" href=
"#dt-predicate">predicates</a> with a sequence of nodes selected
using a <b>reverse axis</b>, it is important to remember that the
the context positions for such a sequence are assigned in <a title=
"reverse document order" href="#dt-reverse-document-order">reverse
document order</a>. For example, <code>preceding::foo[1]</code>
returns the first qualifying <code>foo</code> element in <a title=
"reverse document order" href="#dt-reverse-document-order">reverse
document order</a>, because the predicate is part of an <a title=
"axis step" href="#dt-axis-step">axis step</a> using a reverse
axis. By contrast, <code>(preceding::foo)[1]</code> returns the
first qualifying <code>foo</code> element in <a title=
"document order" href="#dt-document-order">document order</a>,
because the parentheses cause <code>(preceding::foo)</code> to be
parsed as a <a title="primary expression" href=
"#dt-primary-expression">primary expression</a> in which context
positions are assigned in document order. Similarly,
<code>ancestor::*[1]</code> returns the nearest ancestor element,
because the <code>ancestor</code> axis is a reverse axis, whereas
<code>(ancestor::*)[1]</code> returns the root element (first
ancestor in document order).</p>
<p>The fact that a reverse-axis step assigns context positions in
reverse document order for the purpose of evaluating predicates
does not alter the fact that the final result of the step
<span class="xquery"><span class="xquery">(when in ordered
mode)</span></span> is always in document order.</p>
</div>
</div>
<div class="div3">
<h4><a name="unabbrev" id="unabbrev"></a>3.2.3 Unabbreviated
Syntax</h4>
<p>This section provides a number of examples of path expressions
in which the axis is explicitly specified in each <a title="step"
href="#dt-step">step</a>. The syntax used in these examples is
called the <b>unabbreviated syntax</b>. In many common cases, it is
possible to write path expressions more concisely using an
<b>abbreviated syntax</b>, as explained in <a href=
"#abbrev"><b>3.2.4 Abbreviated Syntax</b></a>.</p>
<ul>
<li>
<p><code>child::para</code> selects the <code>para</code> element
children of the context node</p>
</li>
<li>
<p><code>child::*</code> selects all element children of the
context node</p>
</li>
<li>
<p><code>child::text()</code> selects all text node children of the
context node</p>
</li>
<li>
<p><code>child::node()</code> selects all the children of the
context node. Note that no attribute nodes are returned, because
attributes are not children.</p>
</li>
<li>
<p><code>attribute::name</code> selects the <code>name</code>
attribute of the context node</p>
</li>
<li>
<p><code>attribute::*</code> selects all the attributes of the
context node</p>
</li>
<li>
<p><code>parent::node()</code> selects the parent of the context
node. If the context node is an attribute node, this expression
returns the element node (if any) to which the attribute node is
attached.</p>
</li>
<li>
<p><code>descendant::para</code> selects the <code>para</code>
element descendants of the context node</p>
</li>
<li>
<p><code>ancestor::div</code> selects all <code>div</code>
ancestors of the context node</p>
</li>
<li>
<p><code>ancestor-or-self::div</code> selects the <code>div</code>
ancestors of the context node and, if the context node is a
<code>div</code> element, the context node as well</p>
</li>
<li>
<p><code>descendant-or-self::para</code> selects the
<code>para</code> element descendants of the context node and, if
the context node is a <code>para</code> element, the context node
as well</p>
</li>
<li>
<p><code>self::para</code> selects the context node if it is a
<code>para</code> element, and otherwise returns an empty
sequence</p>
</li>
<li>
<p><code>child::chapter/descendant::para</code> selects the
<code>para</code> element descendants of the <code>chapter</code>
element children of the context node</p>
</li>
<li>
<p><code>child::*/child::para</code> selects all <code>para</code>
grandchildren of the context node</p>
</li>
<li>
<p><code>/</code> selects the root of the tree that contains the
context node, but raises a dynamic error if this root is not a
document node</p>
</li>
<li>
<p><code>/descendant::para</code> selects all the <code>para</code>
elements in the same document as the context node</p>
</li>
<li>
<p><code>/descendant::list/child::member</code> selects all the
<code>member</code> elements that have a <code>list</code> parent
and that are in the same document as the context node</p>
</li>
<li>
<p><code>child::para[fn:position() = 1]</code> selects the first
<code>para</code> child of the context node</p>
</li>
<li>
<p><code>child::para[fn:position() = fn:last()]</code> selects the
last <code>para</code> child of the context node</p>
</li>
<li>
<p><code>child::para[fn:position() = fn:last()-1]</code> selects
the last but one <code>para</code> child of the context node</p>
</li>
<li>
<p><code>child::para[fn:position() &gt; 1]</code> selects all the
<code>para</code> children of the context node other than the first
<code>para</code> child of the context node</p>
</li>
<li>
<p><code>following-sibling::chapter[fn:position() =
1]</code>selects the next <code>chapter</code> sibling of the
context node</p>
</li>
<li>
<p><code>preceding-sibling::chapter[fn:position() =
1]</code>selects the previous <code>chapter</code> sibling of the
context node</p>
</li>
<li>
<p><code>/descendant::figure[fn:position() = 42]</code> selects the
forty-second <code>figure</code> element in the document containing
the context node</p>
</li>
<li>
<p><code>/child::book/child::chapter[fn:position() =
5]/child::section[fn:position() = 2]</code> selects the second
<code>section</code> of the fifth <code>chapter</code> of the
<code>book</code> whose parent is the document node that contains
the context node</p>
</li>
<li>
<p><code>child::para[attribute::type eq "warning"]</code>selects
all <code>para</code> children of the context node that have a
<code>type</code> attribute with value <code>warning</code></p>
</li>
<li>
<p><code>child::para[attribute::type eq 'warning'][fn:position() =
5]</code>selects the fifth <code>para</code> child of the context
node that has a <code>type</code> attribute with value
<code>warning</code></p>
</li>
<li>
<p><code>child::para[fn:position() = 5][attribute::type eq
"warning"]</code>selects the fifth <code>para</code> child of the
context node if that child has a <code>type</code> attribute with
value <code>warning</code></p>
</li>
<li>
<p><code>child::chapter[child::title =
'Introduction']</code>selects the <code>chapter</code> children of
the context node that have one or more <code>title</code> children
whose <a title="typed value" href="#dt-typed-value">typed value</a>
is equal to the string <code>Introduction</code></p>
</li>
<li>
<p><code>child::chapter[child::title]</code> selects the
<code>chapter</code> children of the context node that have one or
more <code>title</code> children</p>
</li>
<li>
<p><code>child::*[self::chapter or self::appendix]</code> selects
the <code>chapter</code> and <code>appendix</code> children of the
context node</p>
</li>
<li>
<p><code>child::*[self::chapter or self::appendix][fn:position() =
fn:last()]</code> selects the last <code>chapter</code> or
<code>appendix</code> child of the context node</p>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="abbrev" id="abbrev"></a>3.2.4 Abbreviated Syntax</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AbbrevForwardStep" id=
"doc-xquery-AbbrevForwardStep"></a>[74]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AbbrevForwardStep">AbbrevForwardStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"@"? <a href=
"#doc-xquery-NodeTest">NodeTest</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AbbrevReverseStep" id=
"doc-xquery-AbbrevReverseStep"></a>[77]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AbbrevReverseStep">AbbrevReverseStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>".."</code></td>
</tr>
</tbody>
</table>
<p>The abbreviated syntax permits the following abbreviations:</p>
<ol class="enumar">
<li>
<p>The attribute axis <code>attribute::</code> can be abbreviated
by <code>@</code>. For example, a path expression
<code>para[@type="warning"]</code> is short for
<code>child::para[attribute::type="warning"]</code> and so selects
<code>para</code> children with a <code>type</code> attribute with
value equal to <code>warning</code>.</p>
</li>
<li>
<p>If the axis name is omitted from an <a title="axis step" href=
"#dt-axis-step">axis step</a>, the default axis is
<code>child</code> unless the axis step contains an <a href=
"#doc-xquery-AttributeTest">AttributeTest</a> or <a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a>; in that
case, the default axis is <code>attribute</code>. For example, the
path expression <code>section/para</code> is an abbreviation for
<code>child::section/child::para</code>, and the path expression
<code>section/@id</code> is an abbreviation for
<code>child::section/attribute::id</code>. Similarly,
<code>section/attribute(id)</code> is an abbreviation for
<code>child::section/attribute::attribute(id)</code>. Note that the
latter expression contains both an axis specification and a
<a title="node test" href="#dt-node-test">node test</a>.</p>
</li>
<li>
<p>Each non-initial occurrence of <code>//</code> is effectively
replaced by <code>/descendant-or-self::node()/</code> during
processing of a path expression. For example,
<code>div1//para</code> is short for
<code>child::div1/descendant-or-self::node()/child::para</code> and
so will select all <code>para</code> descendants of
<code>div1</code> children.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The path expression <code>//para[1]</code> does <em>not</em>
mean the same as the path expression
<code>/descendant::para[1]</code>. The latter selects the first
descendant <code>para</code> element; the former selects all
descendant <code>para</code> elements that are the first
<code>para</code> children of their respective parents.</p>
</div>
</li>
<li>
<p>A step consisting of <code>..</code> is short for
<code>parent::node()</code>. For example, <code>../title</code> is
short for <code>parent::node()/child::title</code> and so will
select the <code>title</code> children of the parent of the context
node.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The expression <code>.</code>, known as a <b>context item
expression</b>, is a <a title="primary expression" href=
"#dt-primary-expression">primary expression</a>, and is described
in <a href="#id-context-item-expression"><b>3.1.4 Context Item
Expression</b></a>.</p>
</div>
</li>
</ol>
<p>Here are some examples of path expressions that use the
abbreviated syntax:</p>
<ul>
<li>
<p><code>para</code> selects the <code>para</code> element children
of the context node</p>
</li>
<li>
<p><code>*</code> selects all element children of the context
node</p>
</li>
<li>
<p><code>text()</code> selects all text node children of the
context node</p>
</li>
<li>
<p><code>@name</code> selects the <code>name</code> attribute of
the context node</p>
</li>
<li>
<p><code>@*</code> selects all the attributes of the context
node</p>
</li>
<li>
<p><code>para[1]</code> selects the first <code>para</code> child
of the context node</p>
</li>
<li>
<p><code>para[fn:last()]</code> selects the last <code>para</code>
child of the context node</p>
</li>
<li>
<p><code>*/para</code> selects all <code>para</code> grandchildren
of the context node</p>
</li>
<li>
<p><code>/book/chapter[5]/section[2]</code> selects the second
<code>section</code> of the fifth <code>chapter</code> of the
<code>book</code> whose parent is the document node that contains
the context node</p>
</li>
<li>
<p><code>chapter//para</code> selects the <code>para</code> element
descendants of the <code>chapter</code> element children of the
context node</p>
</li>
<li>
<p><code>//para</code> selects all the <code>para</code>
descendants of the root document node and thus selects all
<code>para</code> elements in the same document as the context
node</p>
</li>
<li>
<p><code>//@version</code> selects all the <code>version</code>
attribute nodes that are in the same document as the context
node</p>
</li>
<li>
<p><code>//list/member</code> selects all the <code>member</code>
elements in the same document as the context node that have a
<code>list</code> parent</p>
</li>
<li>
<p><code>.//para</code> selects the <code>para</code> element
descendants of the context node</p>
</li>
<li>
<p><code>..</code> selects the parent of the context node</p>
</li>
<li>
<p><code>../@lang</code> selects the <code>lang</code> attribute of
the parent of the context node</p>
</li>
<li>
<p><code>para[@type="warning"]</code> selects all <code>para</code>
children of the context node that have a <code>type</code>
attribute with value <code>warning</code></p>
</li>
<li>
<p><code>para[@type="warning"][5]</code> selects the fifth
<code>para</code> child of the context node that has a
<code>type</code> attribute with value <code>warning</code></p>
</li>
<li>
<p><code>para[5][@type="warning"]</code> selects the fifth
<code>para</code> child of the context node if that child has a
<code>type</code> attribute with value <code>warning</code></p>
</li>
<li>
<p><code>chapter[title="Introduction"]</code> selects the
<code>chapter</code> children of the context node that have one or
more <code>title</code> children whose <a title="typed value" href=
"#dt-typed-value">typed value</a> is equal to the string
<code>Introduction</code></p>
</li>
<li>
<p><code>chapter[title]</code> selects the <code>chapter</code>
children of the context node that have one or more
<code>title</code> children</p>
</li>
<li>
<p><code>employee[@secretary and @assistant]</code> selects all the
<code>employee</code> children of the context node that have both a
<code>secretary</code> attribute and an <code>assistant</code>
attribute</p>
</li>
<li>
<p><code>book/(chapter|appendix)/section</code> selects every
<code>section</code> element that has a parent that is either a
<code>chapter</code> or an <code>appendix</code> element, that in
turn is a child of a <code>book</code> element that is a child of
the context node.</p>
</li>
<li>
<p>If <code>E</code> is any expression that returns a sequence of
nodes, then the expression <code>E/.</code> returns the same nodes
in <a title="document order" href="#dt-document-order">document
order</a>, with duplicates eliminated based on node identity.</p>
</li>
</ul>
</div>
</div>
<div class="div2">
<h3><a name="id-sequence-expressions" id=
"id-sequence-expressions"></a>3.3 Sequence Expressions</h3>
<p>XQuery supports operators to construct, filter, and combine
<a title="sequence" href="#dt-sequence">sequences</a> of <a title=
"item" href="#dt-item">items</a>. Sequences are never nested—for
example, combining the values <code>1</code>, <code>(2, 3)</code>,
and <code>( )</code> into a single sequence results in the sequence
<code>(1, 2, 3)</code>.</p>
<div class="div3">
<h4><a name="construct_seq" id="construct_seq"></a>3.3.1
Constructing Sequences</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e8430.doc-xquery-Expr" id=
"noid_d2e8430.doc-xquery-Expr"></a>[31]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Expr">Expr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ExprSingle">ExprSingle</a> (","
<a href="#doc-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-RangeExpr" id=
"doc-xquery-RangeExpr"></a>[49]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-RangeExpr">RangeExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AdditiveExpr">AdditiveExpr</a> (
"to" <a href="#doc-xquery-AdditiveExpr">AdditiveExpr</a>
)?</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-comma-operator" id="dt-comma-operator" title=
"comma operator">Definition</a>: One way to construct a sequence is
by using the <b>comma operator</b>, which evaluates each of its
operands and concatenates the resulting sequences, in order, into a
single result sequence.] Empty parentheses can be used to denote an
empty sequence.</p>
<p>A sequence may contain duplicate atomic values or nodes, but a
sequence is never an item in another sequence. When a new sequence
is created by concatenating two or more input sequences, the new
sequence contains all the items of the input sequences and its
length is the sum of the lengths of the input sequences.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>In places where the grammar calls for <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>, such as the arguments of a
function call, any expression that contains a top-level comma
operator must be enclosed in parentheses.</p>
</div>
<p>Here are some examples of expressions that construct
sequences:</p>
<ul>
<li>
<p>The result of this expression is a sequence of five
integers:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
(10, 1, 2, 3, 4)
</pre></div>
</div>
</li>
<li>
<p>This expression combines four sequences of length one, two,
zero, and two, respectively, into a single sequence of length five.
The result of this expression is the sequence <code>10, 1, 2, 3,
4</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
(10, (1, 2), (), (3, 4))
</pre></div>
</div>
</li>
<li>
<p>The result of this expression is a sequence containing all
<code>salary</code> children of the context node followed by all
<code>bonus</code> children.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
(salary, bonus)
</pre></div>
</div>
</li>
<li>
<p>Assuming that <code>$price</code> is bound to the value
<code>10.50</code>, the result of this expression is the sequence
<code>10.50, 10.50</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
($price, $price)
</pre></div>
</div>
</li>
</ul>
<p>A <b>range expression</b> can be used to construct a sequence of
consecutive integers. Each of the operands of the <code>to</code>
operator is converted as though it was an argument of a function
with the expected parameter type <code>xs:integer?</code>. If
either operand is an empty sequence, or if the integer derived from
the first operand is greater than the integer derived from the
second operand, the result of the range expression is an empty
sequence. If the two operands convert to the same integer, the
result of the range expression is that integer. Otherwise, the
result is a sequence containing the two integer operands and every
integer between the two operands, in increasing order.</p>
<ul>
<li>
<p>This example uses a range expression as one operand in
constructing a sequence. It evaluates to the sequence <code>10, 1,
2, 3, 4</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
(10, 1 to 4)
</pre></div>
</div>
</li>
<li>
<p>This example constructs a sequence of length one containing the
single integer <code>10</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
10 to 10
</pre></div>
</div>
</li>
<li>
<p>The result of this example is a sequence of length zero.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
15 to 10
</pre></div>
</div>
</li>
<li>
<p>This example uses the <code>fn:reverse</code> function to
construct a sequence of six integers in decreasing order. It
evaluates to the sequence <code>15, 14, 13, 12, 11, 10</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
fn:reverse(10 to 15)
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="id-filter-expr" id="id-filter-expr"></a>3.3.2 Filter
Expressions</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-FilterExpr" id=
"doc-xquery-FilterExpr"></a>[81]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-FilterExpr">FilterExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-PrimaryExpr">PrimaryExpr</a>
<a href="#doc-xquery-PredicateList">PredicateList</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e8538.doc-xquery-PredicateList" id=
"noid_d2e8538.doc-xquery-PredicateList"></a>[82]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-PredicateList">PredicateList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-Predicate">Predicate</a>*</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-filter-expression" id="dt-filter-expression" title=
"filter expression">Definition</a>: A <b>filter expression</b>
consists simply of a <b>primary expression</b> followed by zero or
more <a title="predicate" href="#dt-predicate">predicates</a>. The
result of the filter expression consists of the items returned by
the primary expression, filtered by applying each predicate in
turn, working from left to right.] If no predicates are specified,
the result is simply the result of the primary expression. The
ordering of the items returned by a filter expression is the same
as their order in the result of the primary expression. Context
positions are assigned to items based on their ordinal position in
the result sequence. The first context position is 1.</p>
<p>Here are some examples of filter expressions:</p>
<ul>
<li>
<p>Given a sequence of products in a variable, return only those
products whose price is greater than 100.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$products[price gt 100]
</pre></div>
</div>
</li>
<li>
<p>List all the integers from 1 to 100 that are divisible by 5.
(See <a href="#construct_seq"><b>3.3.1 Constructing
Sequences</b></a> for an explanation of the <code>to</code>
operator.)</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
(1 to 100)[. mod 5 eq 0]
</pre></div>
</div>
</li>
<li>
<p>The result of the following expression is the integer 25:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
(21 to 29)[5]
</pre></div>
</div>
</li>
<li>
<p>The following example returns the fifth through ninth items in
the sequence bound to variable <code>$orders</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$orders[fn:position() = (5 to 9)]
</pre></div>
</div>
</li>
<li>
<p>The following example illustrates the use of a filter expression
as a <a title="step" href="#dt-step">step</a> in a <a title=
"path expression" href="#dt-path-expression">path expression</a>.
It returns the last chapter or appendix within the book bound to
variable <code>$book</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$book/(chapter | appendix)[fn:last()]
</pre></div>
</div>
</li>
<li>
<p>The following example also illustrates the use of a filter
expression as a <a title="step" href="#dt-step">step</a> in a
<a title="path expression" href="#dt-path-expression">path
expression</a>. It returns the element node within the specified
document whose ID value is <code>tiger</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
fn:doc("zoo.xml")/fn:id('tiger')
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="combining_seq" id="combining_seq"></a>3.3.3 Combining
Node Sequences</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-UnionExpr" id=
"doc-xquery-UnionExpr"></a>[52]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-UnionExpr">UnionExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-IntersectExceptExpr">IntersectExceptExpr</a> (
("union" | "|") <a href=
"#doc-xquery-IntersectExceptExpr">IntersectExceptExpr</a>
)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-IntersectExceptExpr" id=
"doc-xquery-IntersectExceptExpr"></a>[53]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-IntersectExceptExpr">IntersectExceptExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-InstanceofExpr">InstanceofExpr</a> (
("intersect" | "except") <a href=
"#doc-xquery-InstanceofExpr">InstanceofExpr</a> )*</code></td>
</tr>
</tbody>
</table>
<p>XQuery provides the following operators for combining sequences
of nodes:</p>
<ul>
<li>
<p>The <code>union</code> and <code>|</code> operators are
equivalent. They take two node sequences as operands and return a
sequence containing all the nodes that occur in either of the
operands.</p>
</li>
<li>
<p>The <code>intersect</code> operator takes two node sequences as
operands and returns a sequence containing all the nodes that occur
in both operands.</p>
</li>
<li>
<p>The <code>except</code> operator takes two node sequences as
operands and returns a sequence containing all the nodes that occur
in the first operand but not in the second operand.</p>
</li>
</ul>
<p>All these operators eliminate duplicate nodes from their result
sequences based on node identity. <span class="xquery"><span class=
"xquery">If <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is <code>ordered</code>, the
resulting sequence is returned in <a title="document order" href=
"#dt-document-order">document order</a>; otherwise it is returned
in <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
order.</span></span></p>
<p>If an operand of <code>union</code>, <code>intersect</code>, or
<code>except</code> contains an item that is not a node, a
<a title="type error" href="#dt-type-error">type error</a> is
raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
<p>Here are some examples of expressions that combine sequences.
Assume the existence of three element nodes that we will refer to
by symbolic names A, B, and C. Assume that the variables
<code>$seq1</code>, <code>$seq2</code> and <code>$seq3</code> are
bound to the following sequences of these nodes:</p>
<ul>
<li>
<p><code>$seq1</code> is bound to (A, B)</p>
</li>
<li>
<p><code>$seq2</code> is bound to (A, B)</p>
</li>
<li>
<p><code>$seq3</code> is bound to (B, C)</p>
</li>
</ul>
<p>Then:</p>
<ul>
<li>
<p><code>$seq1 union $seq2</code> evaluates to the sequence (A,
B).</p>
</li>
<li>
<p><code>$seq2 union $seq3</code> evaluates to the sequence (A, B,
C).</p>
</li>
<li>
<p><code>$seq1 intersect $seq2</code> evaluates to the sequence (A,
B).</p>
</li>
<li>
<p><code>$seq2 intersect $seq3</code> evaluates to the sequence
containing B only.</p>
</li>
<li>
<p><code>$seq1 except $seq2</code> evaluates to the empty
sequence.</p>
</li>
<li>
<p><code>$seq2 except $seq3</code> evaluates to the sequence
containing A only.</p>
</li>
</ul>
<p>In addition to the sequence operators described here, <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a> includes functions for indexed
access to items or sub-sequences of a sequence, for indexed
insertion or removal of items in a sequence, and for removing
duplicate items from a sequence.</p>
</div>
</div>
<div class="div2">
<h3><a name="id-arithmetic" id="id-arithmetic"></a>3.4 Arithmetic
Expressions</h3>
<p>XQuery provides arithmetic operators for addition, subtraction,
multiplication, division, and modulus, in their usual binary and
unary forms.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AdditiveExpr" id=
"doc-xquery-AdditiveExpr"></a>[50]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AdditiveExpr">AdditiveExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-MultiplicativeExpr">MultiplicativeExpr</a> ( ("+" |
"-") <a href=
"#doc-xquery-MultiplicativeExpr">MultiplicativeExpr</a>
)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-MultiplicativeExpr" id=
"doc-xquery-MultiplicativeExpr"></a>[51]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-MultiplicativeExpr">MultiplicativeExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-UnionExpr">UnionExpr</a> ( ("*" |
"div" | "idiv" | "mod") <a href=
"#doc-xquery-UnionExpr">UnionExpr</a> )*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-UnaryExpr" id=
"doc-xquery-UnaryExpr"></a>[58]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-UnaryExpr">UnaryExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("-" | "+")* <a href=
"#doc-xquery-ValueExpr">ValueExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ValueExpr" id=
"doc-xquery-ValueExpr"></a>[59]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ValueExpr">ValueExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ValidateExpr">ValidateExpr</a> |
<a href="#doc-xquery-PathExpr">PathExpr</a> | <a href=
"#doc-xquery-ExtensionExpr">ExtensionExpr</a></code></td>
</tr>
</tbody>
</table>
<p>A subtraction operator must be preceded by whitespace if it
could otherwise be interpreted as part of the previous token. For
example, <code>a-b</code> will be interpreted as a name, but
<code>a - b</code> and <code>a -b</code> will be interpreted as
arithmetic expressions. (See <a href="#whitespace-rules"><b>A.2.4
Whitespace Rules</b></a> for further details on whitespace
handling.)</p>
<p>The first step in evaluating an arithmetic expression is to
evaluate its operands. The order in which the operands are
evaluated is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
<p><span class="xquery"><span class="xquery">Each</span></span>
operand is evaluated by applying the following steps, in order:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the operand. The result of this operation is called the
<b>atomized operand</b>.</p>
</li>
<li>
<p>If the atomized operand is an empty sequence, the result of the
arithmetic expression is an empty sequence, and the implementation
need not evaluate the other operand or apply the operator. However,
an implementation may choose to evaluate the other operand in order
to determine whether it raises an error.</p>
</li>
<li>
<p>If the atomized operand is a sequence of length greater than
one, a <a title="type error" href="#dt-type-error">type error</a>
is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the atomized operand is of type
<code>xs:untypedAtomic</code>, it is cast to
<code>xs:double</code>. If the cast fails, a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a> is
raised. [err:FORG0001]</p>
</li>
</ol>
<p>After evaluation of the operands, if the types of the operands
are a valid combination for the given arithmetic operator, the
operator is applied to the operands, resulting in an atomic value
or a <a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a> (for example, an error might result from dividing by
zero.) The combinations of atomic types that are accepted by the
various arithmetic operators, and their respective result types,
are listed in <a href="#mapping"><b>B.2 Operator Mapping</b></a>
together with the <a title="operator function" href=
"#dt-operator-function">operator functions</a> that define the
semantics of the operator for each type combination, including the
dynamic errors that can be raised by the operator. The definitions
of the operator functions are found in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
<p>If the types of the operands, after evaluation, are not a valid
combination for the given operator, according to the rules in
<a href="#mapping"><b>B.2 Operator Mapping</b></a>, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].</p>
<p>XQuery supports two division operators named <code>div</code>
and <code>idiv</code>. Each of these operators accepts two operands
of any <a title="numeric" href="#dt-numeric">numeric</a> type. As
described in <a href="#FunctionsAndOperators">[XQuery 1.0 and XPath
2.0 Functions and Operators (Second Edition)]</a>, <code>$arg1 idiv
$arg2</code> is equivalent to <code>($arg1 div $arg2) cast as
xs:integer?</code> except for error cases.</p>
<p>Here are some examples of arithmetic expressions:</p>
<ul>
<li>
<p>The first expression below returns the <code>xs:decimal</code>
value <code>-1.5</code>, and the second expression returns the
<code>xs:integer</code> value <code>-1</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
-3 div 2
-3 idiv 2
</pre></div>
</div>
</li>
<li>
<p>Subtraction of two date values results in a value of type
<code>xs:dayTimeDuration</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$emp/hiredate - $emp/birthdate
</pre></div>
</div>
</li>
<li>
<p>This example illustrates the difference between a subtraction
operator and a hyphen:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$unit-price - $unit-discount
</pre></div>
</div>
</li>
<li>
<p>Unary operators have higher precedence than binary operators,
subject of course to the use of parentheses. Therefore, the
following two examples have different meanings:</p>
<div class="exampleInner">
<pre>
-$bellcost + $whistlecost
-($bellcost + $whistlecost)
</pre></div>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p id="note-consecutive-unary-ops">Multiple consecutive unary
arithmetic operators are permitted by XQuery for compatibility with
<a href="#XPath">[XPath 1.0]</a>.</p>
</div>
</div>
<div class="div2">
<h3><a name="id-comparisons" id="id-comparisons"></a>3.5 Comparison
Expressions</h3>
<p>Comparison expressions allow two values to be compared. XQuery
provides three kinds of comparison expressions, called value
comparisons, general comparisons, and node comparisons.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ComparisonExpr" id=
"doc-xquery-ComparisonExpr"></a>[48]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ComparisonExpr">ComparisonExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-RangeExpr">RangeExpr</a> ( (<a href=
"#doc-xquery-ValueComp">ValueComp</a><br />
| <a href="#doc-xquery-GeneralComp">GeneralComp</a><br />
| <a href="#doc-xquery-NodeComp">NodeComp</a>) <a href=
"#doc-xquery-RangeExpr">RangeExpr</a> )?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ValueComp" id=
"doc-xquery-ValueComp"></a>[61]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ValueComp">ValueComp</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"eq" | "ne" | "lt" | "le" | "gt" | "ge"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-GeneralComp" id=
"doc-xquery-GeneralComp"></a>[60]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-GeneralComp">GeneralComp</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"=" | "!=" | "&lt;" | "&lt;=" | "&gt;" |
"&gt;="</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-NodeComp" id=
"doc-xquery-NodeComp"></a>[62]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-NodeComp">NodeComp</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"is" | "&lt;&lt;" | "&gt;&gt;"</code></td>
</tr>
</tbody>
</table>
<div class="div3">
<h4><a name="id-value-comparisons" id=
"id-value-comparisons"></a>3.5.1 Value Comparisons</h4>
<p>The value comparison operators are <code>eq</code>,
<code>ne</code>, <code>lt</code>, <code>le</code>, <code>gt</code>,
and <code>ge</code>. Value comparisons are used for comparing
single values.</p>
<p>The first step in evaluating a value comparison is to evaluate
its operands. The order in which the operands are evaluated is
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>. Each
operand is evaluated by applying the following steps, in order:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the operand. The result of this operation is called the
<b>atomized operand</b>.</p>
</li>
<li>
<p>If the atomized operand is an empty sequence, the result of the
value comparison is an empty sequence, and the implementation need
not evaluate the other operand or apply the operator. However, an
implementation may choose to evaluate the other operand in order to
determine whether it raises an error.</p>
</li>
<li>
<p>If the atomized operand is a sequence of length greater than
one, a <a title="type error" href="#dt-type-error">type error</a>
is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the atomized operand is of type
<code>xs:untypedAtomic</code>, it is cast to
<code>xs:string</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The purpose of this rule is to make value comparisons
transitive. Users should be aware that the general comparison
operators have a different rule for casting of
<code>xs:untypedAtomic</code> operands. Users should also be aware
that transitivity of value comparisons may be compromised by loss
of precision during type conversion (for example, two
<code>xs:integer</code> values that differ slightly may both be
considered equal to the same <code>xs:float</code> value because
<code>xs:float</code> has less precision than
<code>xs:integer</code>).</p>
</div>
</li>
</ol>
<p>Next, if possible, the two operands are converted to their least
common type by a combination of <a title="type promotion" href=
"#dt-type-promotion">type promotion</a> and <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a>. For example, if the operands are of type
<code>hatsize</code> (derived from <code>xs:integer</code>) and
<code>shoesize</code> (derived from <code>xs:float</code>), their
least common type is <code>xs:float</code>.</p>
<p>Finally, if the types of the operands are a valid combination
for the given operator, the operator is applied to the operands.
The combinations of atomic types that are accepted by the various
value comparison operators, and their respective result types, are
listed in <a href="#mapping"><b>B.2 Operator Mapping</b></a>
together with the <a title="operator function" href=
"#dt-operator-function">operator functions</a> that define the
semantics of the operator for each type combination. The
definitions of the operator functions are found in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
<p>Informally, if both atomized operands consist of exactly one
atomic value, then the result of the comparison is
<code>true</code> if the value of the first operand is (equal, not
equal, less than, less than or equal, greater than, greater than or
equal) to the value of the second operand; otherwise the result of
the comparison is <code>false</code>.</p>
<p>If the types of the operands, after evaluation, are not a valid
combination for the given operator, according to the rules in
<a href="#mapping"><b>B.2 Operator Mapping</b></a>, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].</p>
<p>Here are some examples of value comparisons:</p>
<ul>
<li>
<p>The following comparison atomizes the node(s) that are returned
by the expression <code>$book/author</code>. The comparison is true
only if the result of atomization is the value "Kennedy" as an
instance of <code>xs:string</code> or
<code>xs:untypedAtomic</code>. If the result of atomization is an
empty sequence, the result of the comparison is an empty sequence.
If the result of atomization is a sequence containing more than one
value, a <a title="type error" href="#dt-type-error">type error</a>
is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$book1/author eq "Kennedy"
</pre></div>
</div>
</li>
<li>
<p>The following <a title="path expression" href=
"#dt-path-expression">path expression</a> contains a predicate that
selects products whose weight is greater than 100. For any product
that does not have a <code>weight</code> subelement, the value of
the predicate is the empty sequence, and the product is not
selected. This example assumes that <code>weight</code> is a
validated element with a numeric type.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
//product[weight gt 100]
</pre></div>
</div>
</li>
<li class="xquery">
<p>The following comparisons are true because, in each case, the
two constructed nodes have the same value after atomization, even
though they have different identities and/or names:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;5&lt;/a&gt; eq &lt;a&gt;5&lt;/a&gt;
</pre></div>
</div>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;5&lt;/a&gt; eq &lt;b&gt;5&lt;/b&gt;
</pre></div>
</div>
</li>
<li>
<p>The following comparison is true if <code>my:hatsize</code> and
<code>my:shoesize</code> are both user-defined types that are
derived by restriction from a primitive <a title="numeric" href=
"#dt-numeric">numeric</a> type:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
my:hatsize(5) eq my:shoesize(5)
</pre></div>
</div>
</li>
<li>
<p>The following comparison is true. The <code>eq</code> operator
compares two QNames by performing codepoint-comparisons of their
namespace URIs and their local names, ignoring their namespace
prefixes.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
fn:QName("http://example.com/ns1", "this:color")
   eq fn:QName("http://example.com/ns1", "that:color")
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="id-general-comparisons" id=
"id-general-comparisons"></a>3.5.2 General Comparisons</h4>
<p>The general comparison operators are <code>=</code>,
<code>!=</code>, <code>&lt;</code>, <code>&lt;=</code>,
<code>&gt;</code>, and <code>&gt;=</code>. General comparisons are
existentially quantified comparisons that may be applied to operand
sequences of any length. The result of a general comparison that
does not raise an error is always <code>true</code> or
<code>false</code>.</p>
<p><span class="xquery"><span class="xquery">A</span></span>
general comparison is evaluated by applying the following rules, in
order:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to each operand. After atomization, each operand is a
sequence of atomic values.</p>
</li>
<li>
<p>The result of the comparison is <code>true</code> if and only if
there is a pair of atomic values, one in the first operand sequence
and the other in the second operand sequence, that have the
required <b>magnitude relationship</b>. Otherwise the result of the
comparison is <code>false</code>. The <b>magnitude relationship</b>
between two atomic values is determined by applying the following
rules. If a <code>cast</code> operation called for by these rules
is not successful, a dynamic error is raised. [err:FORG0001]</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The purpose of these rules is to preserve compatibility with
XPath 1.0, in which (for example) <code>x &lt; 17</code> is a
numeric comparison if <code>x</code> is an untyped value. Users
should be aware that the value comparison operators have different
rules for casting of <code>xs:untypedAtomic</code> operands.</p>
</div>
<ol class="enumla">
<li>
<p>If both atomic values are instances of
<code>xs:untypedAtomic</code>, then the values are cast to the type
<code>xs:string</code>.</p>
</li>
<li>
<p>If exactly one of the atomic values is an instance of
<code>xs:untypedAtomic</code>, it is cast to a type depending on
the other value's dynamic type T according to the following rules,
in which V denotes the value to be cast:</p>
<ol class="enumlr">
<li>
<p>If T is a numeric type or is derived from a numeric type, then V
is cast to <code>xs:double</code>.</p>
</li>
<li>
<p>If T is <code>xs:dayTimeDuration</code> or is derived from
<code>xs:dayTimeDuration</code>, then V is cast to
<code>xs:dayTimeDuration</code>.</p>
</li>
<li>
<p>If T is <code>xs:yearMonthDuration</code> or is derived from
<code>xs:yearMonthDuration</code>, then V is cast to
<code>xs:yearMonthDuration</code>.</p>
</li>
<li>
<p>In all other cases, V is cast to the primitive base type of
T.</p>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The special treatment of the duration types is required to avoid
errors that may arise when comparing the primitive type
<code>xs:duration</code> with any duration type.</p>
</div>
</li>
<li>
<p>After performing the conversions described above, the atomic
values are compared using one of the value comparison operators
<code>eq</code>, <code>ne</code>, <code>lt</code>, <code>le</code>,
<code>gt</code>, or <code>ge</code>, depending on whether the
general comparison operator was <code>=</code>, <code>!=</code>,
<code>&lt;</code>, <code>&lt;=</code>, <code>&gt;</code>, or
<code>&gt;=</code>. The values have the required <b>magnitude
relationship</b> if and only if the result of this value comparison
is <code>true</code>.</p>
</li>
</ol>
</li>
</ol>
<p>When evaluating a general comparison in which either operand is
a sequence of items, an implementation may return <code>true</code>
as soon as it finds an item in the first operand and an item in the
second operand that have the required <b>magnitude
relationship</b>. Similarly, a general comparison may raise a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
as soon as it encounters an error in evaluating either operand, or
in comparing a pair of items from the two operands. As a result of
these rules, the result of a general comparison is not
deterministic in the presence of errors.</p>
<p>Here are some examples of general comparisons:</p>
<ul>
<li>
<p>The following comparison is true if the <a title="typed value"
href="#dt-typed-value">typed value</a> of any <code>author</code>
subelement of <code>$book1</code> is "Kennedy" as an instance of
<code>xs:string</code> or <code>xs:untypedAtomic</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$book1/author = "Kennedy"
</pre></div>
</div>
</li>
<li>
<p>The following example contains three general comparisons. The
value of the first two comparisons is <code>true</code>, and the
value of the third comparison is <code>false</code>. This example
illustrates the fact that general comparisons are not
transitive.</p>
<div class="exampleInner">
<pre>
(1, 2) = (2, 3)
(2, 3) = (3, 4)
(1, 2) = (3, 4)
</pre></div>
</li>
<li>
<p>The following example contains two general comparisons, both of
which are <code>true</code>. This example illustrates the fact that
the <code>=</code> and <code>!=</code> operators are not inverses
of each other.</p>
<div class="exampleInner">
<pre>
(1, 2) = (2, 3)
(1, 2) != (2, 3)
</pre></div>
</li>
<li>
<p>Suppose that <code>$a</code>, <code>$b</code>, and
<code>$c</code> are bound to element nodes with type annotation
<code>xs:untypedAtomic</code>, with <a title="string value" href=
"#dt-string-value">string values</a> "<code>1</code>",
"<code>2</code>", and "<code>2.0</code>" respectively. Then
<code>($a, $b) = ($c, 3.0)</code> returns <code>false</code>,
because <code>$b</code> and <code>$c</code> are compared as
strings. However, <code>($a, $b) = ($c, 2.0)</code> returns
<code>true</code>, because <code>$b</code> and <code>2.0</code> are
compared as numbers.</p>
</li>
</ul>
</div>
<div class="div3">
<h4><a name="id-node-comparisons" id=
"id-node-comparisons"></a>3.5.3 Node Comparisons</h4>
<p>Node comparisons are used to compare two nodes, by their
identity or by their <a title="document order" href=
"#dt-document-order">document order</a>. The result of a node
comparison is defined by the following rules:</p>
<ol class="enumar">
<li>
<p>The operands of a node comparison are evaluated in <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
order.</p>
</li>
<li>
<p>If either operand is an empty sequence, the result of the
comparison is an empty sequence, and the implementation need not
evaluate the other operand or apply the operator. However, an
implementation may choose to evaluate the other operand in order to
determine whether it raises an error.</p>
</li>
<li>
<p>Each operand must be either a single node or an empty sequence;
otherwise a <a title="type error" href="#dt-type-error">type
error</a> is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>A comparison with the <code>is</code> operator is
<code>true</code> if the two operand nodes have the same identity,
and are thus the same node; otherwise it is <code>false</code>. See
<a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a> for a definition of node identity.</p>
</li>
<li>
<p>A comparison with the <code>&lt;&lt;</code> operator returns
<code>true</code> if the left operand node precedes the right
operand node in <a title="document order" href=
"#dt-document-order">document order</a>; otherwise it returns
<code>false</code>.</p>
</li>
<li>
<p>A comparison with the <code>&gt;&gt;</code> operator returns
<code>true</code> if the left operand node follows the right
operand node in <a title="document order" href=
"#dt-document-order">document order</a>; otherwise it returns
<code>false</code>.</p>
</li>
</ol>
<p>Here are some examples of node comparisons:</p>
<ul>
<li>
<p>The following comparison is true only if the left and right
sides each evaluate to exactly the same single node:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
/books/book[isbn="1558604820"] is /books/book[call="QA76.9 C3845"]
</pre></div>
</div>
</li>
<li class="xquery">
<p>The following comparison is false because each constructed node
has its own identity:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;5&lt;/a&gt; is &lt;a&gt;5&lt;/a&gt;
</pre></div>
</div>
</li>
<li>
<p>The following comparison is true only if the node identified by
the left side occurs before the node identified by the right side
in document order:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
/transactions/purchase[parcel="28-451"] 
   &lt;&lt; /transactions/sale[parcel="33-870"]
</pre></div>
</div>
</li>
</ul>
</div>
</div>
<div class="div2">
<h3><a name="id-logical-expressions" id=
"id-logical-expressions"></a>3.6 Logical Expressions</h3>
<p>A <b>logical expression</b> is either an <b>and-expression</b>
or an <b>or-expression</b>. If a logical expression does not raise
an error, its value is always one of the boolean values
<code>true</code> or <code>false</code>.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrExpr" id=
"doc-xquery-OrExpr"></a>[46]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrExpr">OrExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AndExpr">AndExpr</a> ( "or" <a href=
"#doc-xquery-AndExpr">AndExpr</a> )*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AndExpr" id=
"doc-xquery-AndExpr"></a>[47]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AndExpr">AndExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ComparisonExpr">ComparisonExpr</a> (
"and" <a href="#doc-xquery-ComparisonExpr">ComparisonExpr</a>
)*</code></td>
</tr>
</tbody>
</table>
<p>The first step in evaluating a logical expression is to find the
<a title="effective boolean value" href="#dt-ebv">effective boolean
value</a> of each of its operands (see <a href="#id-ebv"><b>2.4.3
Effective Boolean Value</b></a>).</p>
<p>The value of an and-expression is determined by the effective
boolean values (EBV's) of its operands, as shown in the following
table:</p>
<table border="1" cellpadding="4" cellspacing="1" width="80%"
summary="AND EBV">
<tbody>
<tr>
<td>AND:</td>
<td>EBV<sub>2</sub> = <code>true</code></td>
<td>EBV<sub>2</sub> = <code>false</code></td>
<td>error in EBV<sub>2</sub></td>
</tr>
<tr>
<td>EBV<sub>1</sub> = <code>true</code></td>
<td><code>true</code></td>
<td><code>false</code></td>
<td>error</td>
</tr>
<tr>
<td>EBV<sub>1</sub> = <code>false</code></td>
<td><code>false</code></td>
<td><code>false</code></td>
<td><span class="xquery"><span class="xquery">either
<code>false</code> or error</span></span></td>
</tr>
<tr>
<td>error in EBV<sub>1</sub></td>
<td>error</td>
<td><span class="xquery"><span class="xquery">either
<code>false</code> or error</span></span></td>
<td>error</td>
</tr>
</tbody>
</table>
<p>The value of an or-expression is determined by the effective
boolean values (EBV's) of its operands, as shown in the following
table:</p>
<table border="1" cellpadding="4" cellspacing="1" width="80%"
summary="OR EBV">
<tbody>
<tr>
<td>OR:</td>
<td>EBV<sub>2</sub> = <code>true</code></td>
<td>EBV<sub>2</sub> = <code>false</code></td>
<td>error in EBV<sub>2</sub></td>
</tr>
<tr>
<td>EBV<sub>1</sub> = <code>true</code></td>
<td><code>true</code></td>
<td><code>true</code></td>
<td><span class="xquery"><span class="xquery">either
<code>true</code> or error</span></span></td>
</tr>
<tr>
<td>EBV<sub>1</sub> = <code>false</code></td>
<td><code>true</code></td>
<td><code>false</code></td>
<td>error</td>
</tr>
<tr>
<td>error in EBV<sub>1</sub></td>
<td><span class="xquery"><span class="xquery">either
<code>true</code> or error</span></span></td>
<td>error</td>
<td>error</td>
</tr>
</tbody>
</table>
<p><span class="xquery"><span class="xquery">The order in which the
operands of a logical expression are evaluated is <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>. The
tables above are defined in such a way that</span></span> an
or-expression can return <code>true</code> if the first expression
evaluated is true, and it can raise an error if evaluation of the
first expression raises an error. Similarly, an and-expression can
return <code>false</code> if the first expression evaluated is
false, and it can raise an error if evaluation of the first
expression raises an error. As a result of these rules, a logical
expression is not deterministic in the presence of errors, as
illustrated in the examples below.</p>
<p>Here are some examples of logical expressions:</p>
<ul>
<li>
<p>The following expressions return <code>true</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
1 eq 1 and 2 eq 2
</pre></div>
</div>
<div class="parse-test">
<div class="exampleInner">
<pre>
1 eq 1 or 2 eq 3
</pre></div>
</div>
</li>
<li>
<p>The following expression may return either <code>false</code> or
raise a <a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
1 eq 2 and 3 idiv 0 = 1
</pre></div>
</div>
</li>
<li>
<p>The following expression may return either <code>true</code> or
raise a <a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
1 eq 1 or 3 idiv 0 = 1
</pre></div>
</div>
</li>
<li>
<p>The following expression must raise a <a title="dynamic error"
href="#dt-dynamic-error">dynamic error</a>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
1 eq 1 and 3 idiv 0 = 1
</pre></div>
</div>
</li>
</ul>
<p>In addition to and- and or-expressions, XQuery provides a
function named <code>fn:not</code> that takes a general sequence as
parameter and returns a boolean value. The <code>fn:not</code>
function is defined in <a href="#FunctionsAndOperators">[XQuery 1.0
and XPath 2.0 Functions and Operators (Second Edition)]</a>. The
<code>fn:not</code> function reduces its parameter to an <a title=
"effective boolean value" href="#dt-ebv">effective boolean
value</a>. It then returns <code>true</code> if the effective
boolean value of its parameter is <code>false</code>, and
<code>false</code> if the effective boolean value of its parameter
is <code>true</code>. If an error is encountered in finding the
effective boolean value of its operand, <code>fn:not</code> raises
the same error.</p>
</div>
<div class="xquery">
<div class="div2">
<div class="xquery">
<h3><a name="id-constructors" id="id-constructors"></a>3.7
Constructors</h3>
</div>
<p>XQuery provides constructors that can create XML structures
within a query. Constructors are provided for element, attribute,
document, text, comment, and processing instruction nodes. Two
kinds of constructors are provided: <b>direct constructors</b>,
which use an XML-like notation, and <b>computed constructors</b>,
which use a notation based on enclosed expressions.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Constructor" id=
"doc-xquery-Constructor"></a>[94]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Constructor" class=
"xquery">Constructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirectConstructor">DirectConstructor</a><br />
| <a href=
"#doc-xquery-ComputedConstructor">ComputedConstructor</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirectConstructor" id=
"doc-xquery-DirectConstructor"></a>[95]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirectConstructor" class=
"xquery">DirectConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirElemConstructor">DirElemConstructor</a><br />
| <a href=
"#doc-xquery-DirCommentConstructor">DirCommentConstructor</a><br />
| <a href=
"#doc-xquery-DirPIConstructor">DirPIConstructor</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirElemConstructor" id=
"doc-xquery-DirElemConstructor"></a>[96]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirElemConstructor" class=
"xquery">DirElemConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;" <a href="#prod-xquery-QName">QName</a> <a href=
"#doc-xquery-DirAttributeList">DirAttributeList</a> ("/&gt;" |
("&gt;" <a href="#doc-xquery-DirElemContent">DirElemContent</a>*
"&lt;/" <a href="#prod-xquery-QName">QName</a> <a href=
"#prod-xquery-S">S</a>? "&gt;"))</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirElemContent" id=
"doc-xquery-DirElemContent"></a>[101]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirElemContent" class=
"xquery">DirElemContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirectConstructor">DirectConstructor</a><br />
| <a href="#doc-xquery-CDataSection">CDataSection</a><br />
| <a href="#doc-xquery-CommonContent">CommonContent</a><br />
| <a href=
"#doc-xquery-ElementContentChar">ElementContentChar</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ElementContentChar" id=
"doc-xquery-ElementContentChar"></a>[148]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ElementContentChar" class=
"xquery">ElementContentChar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Char">Char</a> -
[{}&lt;&amp;]</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CommonContent" id=
"doc-xquery-CommonContent"></a>[102]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CommonContent" class=
"xquery">CommonContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PredefinedEntityRef">PredefinedEntityRef</a> |
<a href="#prod-xquery-CharRef">CharRef</a> | "{{" | "}}" | <a href=
"#doc-xquery-EnclosedExpr">EnclosedExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CDataSection" id=
"doc-xquery-CDataSection"></a>[107]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CDataSection" class=
"xquery">CDataSection</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;![CDATA[" <a href=
"#doc-xquery-CDataSectionContents">CDataSectionContents</a>
"]]&gt;"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CDataSectionContents" id=
"doc-xquery-CDataSectionContents"></a>[108]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CDataSectionContents" class=
"xquery">CDataSectionContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>* - (Char* ']]&gt;'
Char*))</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirAttributeList" id=
"doc-xquery-DirAttributeList"></a>[97]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirAttributeList" class=
"xquery">DirAttributeList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-S">S</a> (<a href=
"#prod-xquery-QName">QName</a> <a href="#prod-xquery-S">S</a>? "="
<a href="#prod-xquery-S">S</a>? <a href=
"#doc-xquery-DirAttributeValue">DirAttributeValue</a>)?)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirAttributeValue" id=
"doc-xquery-DirAttributeValue"></a>[98]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirAttributeValue" class=
"xquery">DirAttributeValue</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>('"' (<a href="#doc-xquery-EscapeQuot">EscapeQuot</a> |
<a href=
"#doc-xquery-QuotAttrValueContent">QuotAttrValueContent</a>)*
'"')<br />
| ("'" (<a href="#doc-xquery-EscapeApos">EscapeApos</a> | <a href=
"#doc-xquery-AposAttrValueContent">AposAttrValueContent</a>)*
"'")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-QuotAttrValueContent" id=
"doc-xquery-QuotAttrValueContent"></a>[99]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QuotAttrValueContent" class=
"xquery">QuotAttrValueContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-QuotAttrContentChar">QuotAttrContentChar</a><br />
| <a href="#doc-xquery-CommonContent">CommonContent</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AposAttrValueContent" id=
"doc-xquery-AposAttrValueContent"></a>[100]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AposAttrValueContent" class=
"xquery">AposAttrValueContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AposAttrContentChar">AposAttrContentChar</a><br />
| <a href="#doc-xquery-CommonContent">CommonContent</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-QuotAttrContentChar" id=
"doc-xquery-QuotAttrContentChar"></a>[149]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QuotAttrContentChar" class=
"xquery">QuotAttrContentChar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Char">Char</a> -
["{}&lt;&amp;]</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-AposAttrContentChar" id=
"doc-xquery-AposAttrContentChar"></a>[150]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AposAttrContentChar" class=
"xquery">AposAttrContentChar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Char">Char</a> -
['{}&lt;&amp;]</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-EscapeQuot" id=
"doc-xquery-EscapeQuot"></a>[146]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-EscapeQuot" class=
"xquery">EscapeQuot</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>'""'</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-EscapeApos" id=
"doc-xquery-EscapeApos"></a>[147]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-EscapeApos" class=
"xquery">EscapeApos</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"''"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-EnclosedExpr" id=
"doc-xquery-EnclosedExpr"></a>[29]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-EnclosedExpr" class=
"xquery">EnclosedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"{" <a href="#doc-xquery-Expr">Expr</a> "}"</code></td>
</tr>
</tbody>
</table>
<p>This section contains a conceptual description of the semantics
of various kinds of constructor expressions. An XQuery
implementation is free to use any implementation technique that
produces the same result as the processing steps described in this
section.</p>
<div class="div3">
<h4><a name="id-element-constructor" id=
"id-element-constructor"></a>3.7.1 Direct Element Constructors</h4>
<p>An <b>element constructor</b> creates an element node. [<a name=
"dt-direct-elem-const" id="dt-direct-elem-const" title=
"direct element constructor">Definition</a>: A <b>direct element
constructor</b> is a form of element constructor in which the name
of the constructed element is a constant.] Direct element
constructors are based on standard XML notation. For example, the
following expression is a direct element constructor that creates a
<code>book</code> element containing an attribute and some nested
elements:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;book isbn="isbn-0060229357"&gt;
    &lt;title&gt;Harold and the Purple Crayon&lt;/title&gt;
    &lt;author&gt;
        &lt;first&gt;Crockett&lt;/first&gt;
        &lt;last&gt;Johnson&lt;/last&gt;
    &lt;/author&gt;
&lt;/book&gt;
</pre></div>
</div>
<p>If the element name in a direct element constructor has a
namespace prefix, the namespace prefix is resolved to a namespace
URI using the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>. If the
element name has no namespace prefix, it is implicitly qualified by
the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a>. Note that
both the statically known namespaces and the default element/type
namespace may be affected by <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attributes</a>
found inside the element constructor. The namespace prefix of the
element name is retained after expansion of the QName, as described
in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data Model
(Second Edition)]</a>. The resulting <a title="expanded QName"
href="#dt-expanded-qname">expanded QName</a> becomes the
<code>node-name</code> property of the constructed element
node.</p>
<p>In a direct element constructor, the name used in the end tag
must exactly match the name used in the corresponding start tag,
including its prefix or absence of a prefix.</p>
<p>In a direct element constructor, curly braces { } delimit
<b>enclosed expressions</b>, distinguishing them from literal text.
Enclosed expressions are evaluated and replaced by their value, as
illustrated by the following example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;example&gt;
   &lt;p&gt; Here is a query. &lt;/p&gt;
   &lt;eg&gt; $b/title &lt;/eg&gt;
   &lt;p&gt; Here is the result of the query. &lt;/p&gt;
   &lt;eg&gt;{ $b/title }&lt;/eg&gt;
&lt;/example&gt;
</pre></div>
</div>
<p>The above query might generate the following result (whitespace
has been added for readability to this result and other result
examples in this document):</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;example&gt;
  &lt;p&gt; Here is a query. &lt;/p&gt;
  &lt;eg&gt; $b/title &lt;/eg&gt;
  &lt;p&gt; Here is the result of the query. &lt;/p&gt;
  &lt;eg&gt;&lt;title&gt;Harold and the Purple Crayon&lt;/title&gt;&lt;/eg&gt;
&lt;/example&gt;
</pre></div>
</div>
<p>Since XQuery uses curly braces to denote enclosed expressions,
some convention is needed to denote a curly brace used as an
ordinary character. For this purpose, a pair of identical curly
brace characters within the content of an element or attribute are
interpreted by XQuery as a single curly brace character (that is,
the pair "<code>{{</code>" represents the character
"<code>{</code>" and the pair "<code>}}</code>" represents the
character "<code>}</code>".) Alternatively, the <a title=
"character reference" href="#dt-character-reference">character
references</a> <code>&amp;#x7b;</code> and <code>&amp;#x7d;</code>
can be used to denote curly brace characters. A single left curly
brace ("<code>{</code>") is interpreted as the beginning delimiter
for an enclosed expression. A single right curly brace
("<code>}</code>") without a matching left curly brace is treated
as a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXPST0003" title=
"err:XPST0003">err:XPST0003</a>].</p>
<p>The result of an element constructor is a new element node, with
its own node identity. All the attribute and descendant nodes of
the new element node are also new nodes with their own identities,
even if they are copies of existing nodes.</p>
<div class="div4">
<h5><a name="id-attributes" id="id-attributes"></a>3.7.1.1
Attributes</h5>
<p>The start tag of a direct element constructor may contain one or
more attributes. As in XML, each attribute is specified by a name
and a value. In a direct element constructor, the name of each
attribute is specified by a constant QName, and the value of the
attribute is specified by a string of characters enclosed in single
or double quotes. As in the main content of the element
constructor, an attribute value may contain expressions enclosed in
curly braces, which are evaluated and replaced by their value
during processing of the element constructor.</p>
<p>Each attribute in a direct element constructor creates a new
attribute node, with its own node identity, whose parent is the
constructed element node. However, note that <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attributes</a> (see
<a href="#id-namespaces"><b>3.7.1.2 Namespace Declaration
Attributes</b></a>) do not create attribute nodes.</p>
<p>If an attribute name has a namespace prefix, the prefix is
resolved to a namespace URI using the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>. If the
attribute name has no namespace prefix, the attribute is in no
namespace. Note that the statically known namespaces used in
resolving an attribute name may be affected by <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attributes</a> that
are found inside the same element constructor. The namespace prefix
of the attribute name is retained after expansion of the QName, as
described in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data
Model (Second Edition)]</a>. The resulting <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a>
becomes the <code>node-name</code> property of the constructed
attribute node.</p>
<p>If the attributes in a direct element constructor do not have
distinct <a title="expanded QName" href=
"#dt-expanded-qname">expanded QNames</a> as their respective
<code>node-name</code> properties, a <a title="static error" href=
"#dt-static-error">static error</a> is raised [<a href=
"#ERRXQST0040" title="err:XQST0040">err:XQST0040</a>].</p>
<p>Conceptually, an attribute (other than a namespace declaration
attribute) in a direct element constructor is processed by the
following steps:</p>
<ol class="enumar">
<li>
<p>Each consecutive sequence of literal characters in the attribute
content is treated as a string containing those characters, with
the following exceptions:</p>
<ol class="enumla">
<li>
<p>Each occurrence of two consecutive <code>{</code> characters is
replaced by a single <code>{</code> character.</p>
</li>
<li>
<p>Each occurrence of two consecutive <code>}</code> characters is
replaced by a single <code>}</code> character.</p>
</li>
<li>
<p>Each occurrence of <a href=
"#doc-xquery-EscapeQuot">EscapeQuot</a> is replaced by a single
<code>"</code> character.</p>
</li>
<li>
<p>Each occurrence of <a href=
"#doc-xquery-EscapeApos">EscapeApos</a> is replaced by a single
<code>'</code> character.</p>
</li>
</ol>
<p>Attribute value normalization is then applied to normalize
whitespace and expand <a title="character reference" href=
"#dt-character-reference">character references</a> and <a title=
"predefined entity reference" href=
"#dt-predefined-entity-reference">predefined entity references</a>.
An XQuery processor that supports XML 1.0 uses the rules for
attribute value normalization in Section 3.3.3 of <a href=
"#XML">[XML 1.0]</a>; an XQuery processor that supports XML 1.1
uses the rules for attribute value normalization in Section 3.3.3
of <a href="#XML1.1">[XML 1.1]</a>. In either case, the
normalization rules are applied as though the type of the attribute
were CDATA (leading and trailing whitespace characters are not
stripped.) The choice between XML 1.0 and XML 1.1 rules is
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
</li>
<li>
<p>Each enclosed expression is converted to a string as
follows:</p>
<ol class="enumla">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the value of the enclosed expression, converting it to a
sequence of atomic values.</p>
</li>
<li>
<p>If the result of atomization is an empty sequence, the result is
the zero-length string. Otherwise, each atomic value in the
atomized sequence is cast into a string.</p>
</li>
<li>
<p>The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair.</p>
</li>
</ol>
</li>
<li>
<p>Adjacent strings resulting from the above steps are concatenated
with no intervening blanks. The resulting string becomes the
<code>string-value</code> property of the attribute node. The
attribute node is given a <a title="type annotation" href=
"#dt-type-annotation">type annotation</a> (<code>type-name</code>
property) of <code>xs:untypedAtomic</code> (this type annotation
may change if the parent element is validated). The
<code>typed-value</code> property of the attribute node is the same
as its <code>string-value</code>, as an instance of
<code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>The <code>parent</code> property of the attribute node is set to
the element node constructed by the direct element constructor that
contains this attribute.</p>
</li>
<li>
<p>If the attribute name is <code>xml:id</code>, then
<code>xml:id</code> processing is performed as defined in <a href=
"#XMLID">[XML ID]</a>. This ensures that the attribute has the type
<code>xs:ID</code> and that its value is properly normalized. If an
error is encountered during <code>xml:id</code> processing, an
implementation <a title="may" href="#may">MAY</a> raise a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a>
[<a href="#ERRXQDY0091" title="err:XQDY0091">err:XQDY0091</a>].</p>
</li>
<li>
<p>If the attribute name is <code>xml:id</code>, the
<code>is-id</code> property of the resulting attribute node is set
to <code>true</code>; otherwise the <code>is-id</code> property is
set to <code>false</code>. The <code>is-idrefs</code> property of
the attribute node is unconditionally set to
<code>false</code>.</p>
</li>
</ol>
<ul>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;shoe size="7"/&gt;
</pre></div>
</div>
<p>The string value of the <code>size</code> attribute is
"<code>7</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;shoe size="{7}"/&gt;
</pre></div>
</div>
<p>The string value of the <code>size</code> attribute is
"<code>7</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;shoe size="{()}"/&gt;
</pre></div>
</div>
<p>The string value of the <code>size</code> attribute is the
zero-length string.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;chapter ref="[{1, 5 to 7, 9}]"/&gt;
</pre></div>
</div>
<p>The string value of the <code>ref</code> attribute is "<code>[1
5 6 7 9]</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;shoe size="As big as {$hat/@size}"/&gt;
</pre></div>
</div>
<p>The string value of the <code>size</code> attribute is the
string "<code>As big as</code> ", concatenated with the string
value of the node denoted by the expression
<code>$hat/@size</code>.</p>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="id-namespaces" id="id-namespaces"></a>3.7.1.2
Namespace Declaration Attributes</h5>
<p>The names of a constructed element and its attributes may be
<a title="QName" href="#dt-qname">QNames</a> that include
<b>namespace prefixes</b>. Namespace prefixes can be bound to
namespaces in the <a title="Prolog" href="#dt-prolog">Prolog</a> or
by <b>namespace declaration attributes</b>. It is a <a title=
"static error" href="#dt-static-error">static error</a> to use a
namespace prefix that has not been bound to a namespace [<a href=
"#ERRXPST0081" title="err:XPST0081">err:XPST0081</a>].</p>
<p>[<a name="dt-namespace-decl-attr" id="dt-namespace-decl-attr"
title="namespace declaration attribute">Definition</a>: A
<b>namespace declaration attribute</b> is used inside a direct
element constructor. Its purpose is to bind a namespace prefix or
to set the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a> for the
constructed element node, including its attributes.] Syntactically,
a namespace declaration attribute has the form of an attribute with
namespace prefix <code>xmlns</code>, or with name
<code>xmlns</code> and no namespace prefix. All the namespace
declaration attributes of a given element must have distinct names
[<a href="#ERRXQST0071" title="err:XQST0071">err:XQST0071</a>].
Each namespace declaration attribute is processed as follows:</p>
<ul>
<li>
<p>The value of the namespace declaration attribute (a <a href=
"#doc-xquery-DirAttributeValue">DirAttributeValue</a>) is processed
as follows. If the <a href=
"#doc-xquery-DirAttributeValue">DirAttributeValue</a> contains an
<a href="#doc-xquery-EnclosedExpr">EnclosedExpr</a>, a static error
is raised [<a href="#ERRXQST0022" title=
"err:XQST0022">err:XQST0022</a>]. Otherwise, it is processed as
described in rule 1 of <a href="#id-attributes"><b>3.7.1.1
Attributes</b></a>. An implementation MAY raise a static error
[<a href="#ERRXQST0046" title="err:XQST0046">err:XQST0046</a>] if
the resulting value is of nonzero length and is not in the lexical
space of <code>xs:anyURI</code>. The resulting value is used as the
namespace URI in the following rules.</p>
</li>
<li>
<p>If the prefix of the attribute name is <code>xmlns</code>, then
the local part of the attribute name is interpreted as a namespace
prefix. This prefix and the namespace URI are added to the
<a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> of the
constructor expression (overriding any existing binding of the
given prefix), and are also added as a namespace binding to the
<a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a> of the
constructed element. If the namespace URI is a zero-length string
and the implementation supports <a href="#XMLNAMES11">[XML Names
1.1]</a>, any existing namespace binding for the given prefix is
removed from the <a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a> of the
constructed element and from the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> of the
constructor expression. If the namespace URI is a zero-length
string and the implementation does not support <a href=
"#XMLNAMES11">[XML Names 1.1]</a>, a static error is raised
[<a href="#ERRXQST0085" title="err:XQST0085">err:XQST0085</a>]. It
is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> whether an
implementation supports <a href="#XMLNAMES">[XML Names]</a> or
<a href="#XMLNAMES11">[XML Names 1.1]</a>.</p>
</li>
<li>
<p>If the name of the namespace declaration attribute is
<code>xmlns</code> with no prefix, then the namespace URI specifies
the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a> of the
constructor expression (overriding any existing default), and is
added (with no prefix) to the <a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a> of the
constructed element (overriding any existing namespace binding with
no prefix). If the namespace URI is a zero-length string, the
<a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a> of the
constructor expression is set to "none," and any no-prefix
namespace binding is removed from the <a title=
"in-scope namespaces" href="#dt-in-scope-namespaces">in-scope
namespaces</a> of the constructed element.</p>
</li>
<li>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0070" title=
"err:XQST0070">err:XQST0070</a>] if a namespace declaration
attribute attempts to do any of the following:</p>
<ul>
<li>
<p>Bind the prefix <code>xml</code> to some namespace URI other
than <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>Bind a prefix other than <code>xml</code> to the namespace URI
<code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>Bind the prefix <code>xmlns</code> to any namespace URI.</p>
</li>
<li>
<p>Bind a prefix to the namespace URI
<code>http://www.w3.org/2000/xmlns/</code>.</p>
</li>
</ul>
</li>
</ul>
<p>A namespace declaration attribute does not cause an attribute
node to be created.</p>
<p>The following examples illustrate namespace declaration
attributes:</p>
<ul>
<li>
<p>In this element constructor, a namespace declaration attribute
is used to set the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a> to
<code>http://example.org/animals</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;cat xmlns = "http://example.org/animals"&gt; 
  &lt;breed&gt;Persian&lt;/breed&gt;
&lt;/cat&gt;
</pre></div>
</div>
</li>
<li>
<p>In this element constructor, namespace declaration attributes
are used to bind the namespace prefixes <code>metric</code> and
<code>english</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;box xmlns:metric = "http://example.org/metric/units" 
     xmlns:english = "http://example.org/english/units"&gt; 
  &lt;height&gt;
    &lt;metric:meters&gt;3&lt;/metric:meters&gt; 
  &lt;/height&gt; 
  &lt;width&gt;
    &lt;english:feet&gt;6&lt;/english:feet&gt; 
  &lt;/width&gt; 
  &lt;depth&gt;
    &lt;english:inches&gt;18&lt;/english:inches&gt; 
  &lt;/depth&gt;
&lt;/box&gt;
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="id-content" id="id-content"></a>3.7.1.3 Content</h5>
<p>The part of a direct element constructor between the start tag
and the end tag is called the <b>content</b> of the element
constructor. This content may consist of text characters (parsed as
<a href="#doc-xquery-ElementContentChar">ElementContentChar</a>),
nested direct constructors, <a href=
"#doc-xquery-CDataSection">CdataSections</a>, character and
<a title="predefined entity reference" href=
"#dt-predefined-entity-reference">predefined entity references</a>,
and expressions enclosed in curly braces. In general, the value of
an enclosed expression may be any sequence of nodes and/or atomic
values. Enclosed expressions can be used in the content of an
element constructor to compute both the content and the attributes
of the constructed node.</p>
<p>Conceptually, the content of an element constructor is processed
as follows:</p>
<ol class="enumar">
<li>
<p>The content is evaluated to produce a sequence of nodes called
the <b>content sequence</b>, as follows:</p>
<ol class="enumla">
<li>
<p>If the <a title="boundary-space policy" href=
"#dt-boundary-space-policy">boundary-space policy</a> in the
<a title="static context" href="#dt-static-context">static
context</a> is <code>strip</code>, <a title="boundary whitespace"
href="#dt-boundary-whitespace">boundary whitespace</a> is
identified and deleted (see <a href="#id-whitespace"><b>3.7.1.4
Boundary Whitespace</b></a> for a definition of boundary
whitespace.)</p>
</li>
<li>
<p><a title="predefined entity reference" href=
"#dt-predefined-entity-reference">Predefined entity references</a>
and <a title="character reference" href=
"#dt-character-reference">character references</a> are expanded
into their referenced strings, as described in <a href=
"#id-literals"><b>3.1.1 Literals</b></a>. Characters inside a
<a href="#doc-xquery-CDataSection">CDataSection</a>, including
special characters such as <code>&lt;</code> and
<code>&amp;</code>, are treated as literal characters rather than
as markup characters (except for the sequence <code>]]&gt;</code>,
which terminates the CDataSection).</p>
</li>
<li>
<p>Each consecutive sequence of literal characters evaluates to a
single text node containing the characters.</p>
</li>
<li>
<p>Each nested direct constructor is evaluated according to the
rules in <a href="#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a> or <a href="#id-otherConstructors"><b>3.7.2
Other Direct Constructors</b></a>, resulting in a new element,
comment, or processing instruction node. Then:</p>
<ol class="enumlr">
<li>
<p>The <code>parent</code> property of the resulting node is then
set to the newly constructed element node.</p>
</li>
<li>
<p>The <code>base-uri</code> property of the resulting node, and of
each of its descendants, is set to be the same as that of its new
parent, unless it (the child node) has an <code>xml:base</code>
attribute, in which case its <code>base-uri</code> property is set
to the value of that attribute, resolved (if it is relative)
against the <code>base-uri</code> property of its new parent
node.</p>
</li>
</ol>
</li>
<li>
<p>Enclosed expressions are evaluated as follows:</p>
<ol class="enumlr">
<li>
<p>For each adjacent sequence of one or more atomic values returned
by an enclosed expression, a new text node is constructed,
containing the result of casting each atomic value to a string,
with a single space character inserted between adjacent values.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The insertion of blank characters between adjacent values
applies even if one or both of the values is a zero-length
string.</p>
</div>
</li>
<li>
<p>For each node returned by an enclosed expression, a new copy is
made of the given node and all nodes that have the given node as an
ancestor, collectively referred to as <b>copied nodes</b>. The
properties of the copied nodes are as follows:</p>
<ol class="enumua">
<li>
<p>Each copied node receives a new node identity.</p>
</li>
<li>
<p>The <code>parent</code>, <code>children</code>, and
<code>attributes</code> properties of the copied nodes are set so
as to preserve their inter-node relationships. For the topmost node
(the node directly returned by the enclosed expression), the
<code>parent</code> property is set to the node constructed by this
constructor.</p>
</li>
<li>
<p>If <a title="construction mode" href=
"#dt-construction-mode">construction mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a> is
<code>strip</code>:</p>
<ol class="enumur">
<li>
<p>If the copied node is an element node, its
<code>type-name</code> property is set to <code>xs:untyped</code>.
Its <code>nilled</code>, <code>is-id</code>, and
<code>is-idrefs</code> properties are set to
<code>false</code>.</p>
</li>
<li>
<p>If the copied node is an attribute node, its
<code>type-name</code> property is set to
<code>xs:untypedAtomic</code>. Its <code>is-idrefs</code> property
is set to <code>false</code>. Its <code>is-id</code> property is
set to <code>true</code> if the qualified name of the attribute
node is <code>xml:id</code>; otherwise it is set to
<code>false</code>.</p>
</li>
<li>
<p>The <code>string-value</code> of each copied element and
attribute node remains unchanged, and its <code>typed-value</code>
becomes equal to its <code>string-value</code> as an instance of
<code>xs:untypedAtomic</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Implementations that store only the <a title="typed value" href=
"#dt-typed-value">typed value</a> of a node are required at this
point to convert the typed value to a string form.</p>
</div>
</li>
</ol>
<p>On the other hand, if <a title="construction mode" href=
"#dt-construction-mode">construction mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a> is
<code>preserve</code>, the <code>type-name</code>,
<code>nilled</code>, <code>string-value</code>,
<code>typed-value</code>, <code>is-id</code>, and
<code>is-idrefs</code> properties of the copied nodes are
preserved.</p>
</li>
<li>
<p>The <code>in-scope-namespaces</code> property of a copied
element node is determined by the following rules. In applying
these rules, the default namespace or absence of a default
namespace is treated like any other namespace binding:</p>
<ol class="enumur">
<li>
<p>If <a title="copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> specifies
<code>preserve</code>, all in-scope-namespaces of the original
element are retained in the new copy. If <a title=
"copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> specifies
<code>no-preserve</code>, the new copy retains only those in-scope
namespaces of the original element that are used in the names of
the element and its attributes.</p>
</li>
<li>
<p>If <a title="copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> specifies
<code>inherit</code>, the copied node inherits all the in-scope
namespaces of the constructed node, augmented and overridden by the
in-scope namespaces of the original element that were preserved by
the preceding rule. If <a title="copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> specifies
<code>no-inherit</code>, the copied node does not inherit any
in-scope namespaces from the constructed node.</p>
</li>
</ol>
</li>
<li>
<p>An enclosed expression in the content of an element constructor
may cause one or more existing nodes to be copied. Type error
[<a href="#ERRXQTY0086" title="err:XQTY0086">err:XQTY0086</a>] is
raised in the following cases:</p>
<ol class="enumur">
<li>
<p>An element node is copied, and the <a title="typed value" href=
"#dt-typed-value">typed value</a> of the element node or one of its
attributes is <a title="namespace-sensitive" href=
"#dt-namespace-sensitive">namespace-sensitive</a>, and <a title=
"construction mode" href="#dt-construction-mode">construction
mode</a> is <code>preserve</code>, and <a title=
"copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> is
<code>no-preserve</code>.</p>
</li>
<li>
<p>An attribute node is copied but its parent element node is not
copied, and the <a title="typed value" href="#dt-typed-value">typed
value</a> of the copied attribute node is <a title=
"namespace-sensitive" href=
"#dt-namespace-sensitive">namespace-sensitive</a>, and <a title=
"construction mode" href="#dt-construction-mode">construction
mode</a> is <code>preserve</code>.</p>
</li>
</ol>
<p>[<a name="dt-namespace-sensitive" id="dt-namespace-sensitive"
title="namespace-sensitive">Definition</a>: A value is
<b>namespace-sensitive</b> if it includes an item whose <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a> is
<code>xs:QName</code> or <code>xs:NOTATION</code> or is derived by
restriction from <code>xs:QName</code> or
<code>xs:NOTATION</code>.]</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The rationale for error [<a href="#ERRXQTY0086" title=
"err:XQTY0086">err:XQTY0086</a>] is as follows: It is not possible
to preserve the type of a QName without also preserving the
namespace binding that defines the prefix of the QName.</p>
</div>
</li>
<li>
<p>When an element or processing instruction node is copied, its
<code>base-uri</code> property is set to be the same as that of its
new parent, with the following exception: if a copied element node
has an <code>xml:base</code> attribute, its <code>base-uri</code>
property is set to the value of that attribute, resolved (if it is
relative) against the <code>base-uri</code> property of the new
parent node.</p>
</li>
<li>
<p>All other properties of the copied nodes are preserved.</p>
</li>
</ol>
</li>
</ol>
</li>
</ol>
</li>
<li>
<p>If the content sequence contains a document node, the document
node is replaced in the content sequence by its children.</p>
</li>
<li>
<p>Adjacent text nodes in the content sequence are merged into a
single text node by concatenating their contents, with no
intervening blanks. After concatenation, any text node whose
content is a zero-length string is deleted from the content
sequence.</p>
</li>
<li>
<p>If the content sequence contains an attribute node following a
node that is not an attribute node, a <a title="type error" href=
"#dt-type-error">type error</a> is raised [<a href="#ERRXQTY0024"
title="err:XQTY0024">err:XQTY0024</a>].</p>
</li>
<li>
<p>The properties of the newly constructed element node are
determined as follows:</p>
<ol class="enumla">
<li>
<p><code>node-name</code> is the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> resulting from resolving
the element name in the start tag, including its original namespace
prefix (if any), as described in <a href=
"#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a>.</p>
</li>
<li>
<p><code>parent</code> is set to empty.</p>
</li>
<li>
<p><code>attributes</code> consist of all the attributes specified
in the start tag as described in <a href=
"#id-attributes"><b>3.7.1.1 Attributes</b></a>, together with all
the attribute nodes in the content sequence, in <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> order.
Note that the <code>parent</code> property of each of these
attribute nodes has been set to the newly constructed element node.
If two or more attributes have the same <code>node-name</code>, a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
is raised [<a href="#ERRXQDY0025" title=
"err:XQDY0025">err:XQDY0025</a>]. If an attribute named
<code>xml:space</code> has a value other than <code>preserve</code>
or <code>default</code>, a dynamic error <a title="may" href=
"#may">MAY</a> be raised [<a href="#ERRXQDY0092" title=
"err:XQDY0092">err:XQDY0092</a>].</p>
</li>
<li>
<p><code>children</code> consist of all the element, text, comment,
and processing instruction nodes in the content sequence. Note that
the <code>parent</code> property of each of these nodes has been
set to the newly constructed element node.</p>
</li>
<li>
<p><code>base-uri</code> is set to the following value:</p>
<ol class="enumlr">
<li>
<p>If the constructed node has an attribute named
<code>xml:base</code>, then the value of this attribute, resolved
if it is relative against the <a title="base URI" href=
"#dt-base-uri">base URI</a> in the <a title="base URI" href=
"#dt-base-uri">static context</a>. The value of the
<code>xml:base</code> attribute is normalized as described in
<a href="#XMLBASE">[XML Base]</a>.</p>
</li>
<li>
<p>Otherwise, the value of the <a title="base URI" href=
"#dt-base-uri">base URI</a> in the <a title="base URI" href=
"#dt-base-uri">static context</a>.</p>
</li>
</ol>
</li>
<li>
<p><code>in-scope-namespaces</code> consist of all the namespace
bindings resulting from namespace declaration attributes as
described in <a href="#id-namespaces"><b>3.7.1.2 Namespace
Declaration Attributes</b></a>, and possibly additional namespace
bindings as described in <a href=
"#id-ns-nodes-on-elements"><b>3.7.4 In-scope Namespaces of a
Constructed Element</b></a>.</p>
</li>
<li>
<p>The <code>nilled</code> property is <code>false</code>.</p>
</li>
<li>
<p>The <code>string-value</code> property is equal to the
concatenated contents of the text-node descendants in document
order. If there are no text-node descendants, the
<code>string-value</code> property is a zero-length string.</p>
</li>
<li>
<p>The <code>typed-value</code> property is equal to the
<code>string-value</code> property, as an instance of
<code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>If <a title="construction mode" href=
"#dt-construction-mode">construction mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a> is
<code>strip</code>, the <code>type-name</code> property is
<code>xs:untyped</code>. On the other hand, if construction mode is
<code>preserve</code>, the <code>type-name</code> property is
<code>xs:anyType</code>.</p>
</li>
<li>
<p>The <code>is-id</code> and <code>is-idrefs</code> properties are
set to <code>false</code>.</p>
</li>
</ol>
</li>
</ol>
<ul>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;{1}&lt;/a&gt;
</pre></div>
</div>
<p>The constructed element node has one child, a text node
containing the value "<code>1</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;{1, 2, 3}&lt;/a&gt;
</pre></div>
</div>
<p>The constructed element node has one child, a text node
containing the value "<code>1 2 3</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;c&gt;{1}{2}{3}&lt;/c&gt;
</pre></div>
</div>
<p>The constructed element node has one child, a text node
containing the value "<code>123</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;b&gt;{1, "2", "3"}&lt;/b&gt;
</pre></div>
</div>
<p>The constructed element node has one child, a text node
containing the value "<code>1 2 3</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;fact&gt;I saw 8 cats.&lt;/fact&gt;
</pre></div>
</div>
<p>The constructed element node has one child, a text node
containing the value "<code>I saw 8 cats.</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;fact&gt;I saw {5 + 3} cats.&lt;/fact&gt;
</pre></div>
</div>
<p>The constructed element node has one child, a text node
containing the value "<code>I saw 8 cats.</code>".</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;fact&gt;I saw &lt;howmany&gt;{5 + 3}&lt;/howmany&gt; cats.&lt;/fact&gt;
</pre></div>
</div>
<p>The constructed element node has three children: a text node
containing "<code>I saw</code> ", a child element node named
<code>howmany</code>, and a text node containing "
<code>cats.</code>". The child element node in turn has a single
text node child containing the value "<code>8</code>".</p>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="id-whitespace" id="id-whitespace"></a>3.7.1.4 Boundary
Whitespace</h5>
<p>In a direct element constructor, whitespace characters may
appear in the content of the constructed element. In some cases,
enclosed expressions and/or nested elements may be separated only
by whitespace characters. For example, in the expression below, the
end-tag <code>&lt;/title&gt;</code> and the start-tag
<code>&lt;author&gt;</code> are separated by a newline character
and four space characters:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;book isbn="isbn-0060229357"&gt;
    &lt;title&gt;Harold and the Purple Crayon&lt;/title&gt;
    &lt;author&gt;
        &lt;first&gt;Crockett&lt;/first&gt;
        &lt;last&gt;Johnson&lt;/last&gt;
    &lt;/author&gt;
&lt;/book&gt;
</pre></div>
</div>
<p>[<a name="dt-boundary-whitespace" id="dt-boundary-whitespace"
title="boundary whitespace">Definition</a>: <b>Boundary
whitespace</b> is a sequence of consecutive whitespace characters
within the content of a <a title="direct element constructor" href=
"#dt-direct-elem-const">direct element constructor</a>, that is
delimited at each end either by the start or end of the content, or
by a <a href="#doc-xquery-DirectConstructor">DirectConstructor</a>,
or by an <a href="#doc-xquery-EnclosedExpr">EnclosedExpr</a>. For
this purpose, characters generated by <a title=
"character reference" href="#dt-character-reference">character
references</a> such as <code>&amp;#x20;</code> or by <a href=
"#doc-xquery-CDataSection">CdataSections</a> are not considered to
be whitespace characters.]</p>
<p>The <a title="boundary-space policy" href=
"#dt-boundary-space-policy">boundary-space policy</a> in the
<a title="static context" href="#dt-static-context">static
context</a> controls whether boundary whitespace is preserved by
element constructors. If boundary-space policy is
<code>strip</code>, boundary whitespace is not considered
significant and is discarded. On the other hand, if boundary-space
policy is <code>preserve</code>, boundary whitespace is considered
significant and is preserved.</p>
<ul>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;cat&gt; 
   &lt;breed&gt;{$b}&lt;/breed&gt;
   &lt;color&gt;{$c}&lt;/color&gt; 
&lt;/cat&gt;
</pre></div>
</div>
<p>The constructed <code>cat</code> element node has two child
element nodes named <code>breed</code> and <code>color</code>.
Whitespace surrounding the child elements will be stripped away by
the element constructor if boundary-space policy is
<code>strip</code>.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;  {"abc"}  &lt;/a&gt;
</pre></div>
</div>
<p>If boundary-space policy is <code>strip</code>, this example is
equivalent to <code>&lt;a&gt;abc&lt;/a&gt;</code>. However, if
boundary-space policy is <code>preserve</code>, this example is
equivalent to
<code>&lt;a&gt;&#160;&#160;abc&#160;&#160;&lt;/a&gt;</code>.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt; z {"abc"}&lt;/a&gt;
</pre></div>
</div>
<p>Since the whitespace surrounding the <code>z</code> is not
boundary whitespace, it is always preserved. This example is
equivalent to <code>&lt;a&gt;&#160;z&#160;abc&lt;/a&gt;</code>.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;&amp;#x20;{"abc"}&lt;/a&gt;
</pre></div>
</div>
<p>This example is equivalent to
<code>&lt;a&gt;&#160;abc&lt;/a&gt;</code>, regardless of the
boundary-space policy, because the space generated by the <a title=
"character reference" href="#dt-character-reference">character
reference</a> is not treated as a whitespace character.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;a&gt;{"  "}&lt;/a&gt;
</pre></div>
</div>
<p>This example constructs an element containing two space
characters, regardless of the boundary-space policy, because
whitespace inside an enclosed expression is never considered to be
boundary whitespace.</p>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Element constructors treat attributes named
<code>xml:space</code> as ordinary attributes. An
<code>xml:space</code> attribute does not affect the handling of
whitespace by an element constructor.</p>
</div>
</div>
</div>
<div class="div3">
<h4><a name="id-otherConstructors" id=
"id-otherConstructors"></a>3.7.2 Other Direct Constructors</h4>
<p>XQuery allows an expression to generate a processing instruction
node or a comment node. This can be accomplished by using a
<b>direct processing instruction constructor</b> or a <b>direct
comment constructor</b>. In each case, the syntax of the
constructor expression is based on the syntax of a similar
construct in XML.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirPIConstructor" id=
"doc-xquery-DirPIConstructor"></a>[105]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirPIConstructor" class=
"xquery">DirPIConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;?" <a href="#prod-xquery-PITarget">PITarget</a>
(<a href="#prod-xquery-S">S</a> <a href=
"#doc-xquery-DirPIContents">DirPIContents</a>)? "?&gt;"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirPIContents" id=
"doc-xquery-DirPIContents"></a>[106]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirPIContents" class=
"xquery">DirPIContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>* - (Char* '?&gt;'
Char*))</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirCommentConstructor" id=
"doc-xquery-DirCommentConstructor"></a>[103]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirCommentConstructor" class=
"xquery">DirCommentConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;!--" <a href=
"#doc-xquery-DirCommentContents">DirCommentContents</a>
"--&gt;"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DirCommentContents" id=
"doc-xquery-DirCommentContents"></a>[104]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DirCommentContents" class=
"xquery">DirCommentContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>((<a href="#prod-xquery-Char">Char</a> - '-') | ('-'
(<a href="#prod-xquery-Char">Char</a> - '-')))*</code></td>
</tr>
</tbody>
</table>
<p>A direct processing instruction constructor creates a processing
instruction node whose <code>target</code> property is <a href=
"#prod-xquery-PITarget">PITarget</a> and whose <code>content</code>
property is <a href="#doc-xquery-DirPIContents">DirPIContents</a>.
The <code>base-uri</code> property of the node is empty. The
<code>parent</code> property of the node is empty.</p>
<p>The <a href="#prod-xquery-PITarget">PITarget</a> of a processing
instruction may not consist of the characters "XML" in any
combination of upper and lower case. The <a href=
"#doc-xquery-DirPIContents">DirPIContents</a> of a processing
instruction may not contain the string "<code>?&gt;</code>".</p>
<p>The following example illustrates a direct processing
instruction constructor:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;?format role="output" ?&gt;
</pre></div>
</div>
<p>A direct comment constructor creates a comment node whose
<code>content</code> property is <a href=
"#doc-xquery-DirCommentContents">DirCommentContents</a>. Its
<code>parent</code> property is empty.</p>
<p>The <a href=
"#doc-xquery-DirCommentContents">DirCommentContents</a> of a
comment may not contain two consecutive hyphens or end with a
hyphen. These rules are syntactically enforced by the grammar shown
above.</p>
<p>The following example illustrates a direct comment
constructor:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;!-- Tags are ignored in the following section --&gt;
</pre></div>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>A direct comment constructor is different from a <a href=
"#doc-xquery-Comment">comment</a>, since a direct comment
constructor actually constructs a comment node, whereas a <a href=
"#doc-xquery-Comment">comment</a> is simply used in documenting a
query and is not evaluated.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-computedConstructors" id=
"id-computedConstructors"></a>3.7.3 Computed Constructors</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ComputedConstructor" id=
"doc-xquery-ComputedConstructor"></a>[109]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ComputedConstructor" class=
"xquery">ComputedConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompDocConstructor">CompDocConstructor</a><br />
| <a href=
"#doc-xquery-CompElemConstructor">CompElemConstructor</a><br />
| <a href=
"#doc-xquery-CompAttrConstructor">CompAttrConstructor</a><br />
| <a href=
"#doc-xquery-CompTextConstructor">CompTextConstructor</a><br />
| <a href=
"#doc-xquery-CompCommentConstructor">CompCommentConstructor</a><br />

| <a href=
"#doc-xquery-CompPIConstructor">CompPIConstructor</a></code></td>
</tr>
</tbody>
</table>
<p>An alternative way to create nodes is by using a <b>computed
constructor</b>. A computed constructor begins with a keyword that
identifies the type of node to be created: <code>element</code>,
<code>attribute</code>, <code>document</code>, <code>text</code>,
<code>processing-instruction</code>, or <code>comment</code>.</p>
<p>For those kinds of nodes that have names (element, attribute,
and processing instruction nodes), the keyword that specifies the
node kind is followed by the name of the node to be created. This
name may be specified either as a QName or as an expression
enclosed in braces. [<a name="dt-name-expression" id=
"dt-name-expression" title="name expression">Definition</a>: When
an expression is used to specify the name of a constructed node,
that expression is called the <b>name expression</b> of the
constructor.]</p>
<p>[<a name="dt-content-expression" id="dt-content-expression"
title="content expression">Definition</a>: The final part of a
computed constructor is an expression enclosed in braces, called
the <b>content expression</b> of the constructor, that generates
the content of the node.]</p>
<p>The following example illustrates the use of computed element
and attribute constructors in a simple case where the names of the
constructed nodes are constants. This example generates exactly the
same result as the first example in <a href=
"#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
element book { 
   attribute isbn {"isbn-0060229357" }, 
   element title { "Harold and the Purple Crayon"},
   element author { 
      element first { "Crockett" }, 
      element last {"Johnson" }
   }
}
</pre></div>
</div>
<div class="div4">
<h5><a name="id-computedElements" id=
"id-computedElements"></a>3.7.3.1 Computed Element
Constructors</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CompElemConstructor" id=
"doc-xquery-CompElemConstructor"></a>[111]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CompElemConstructor" class=
"xquery">CompElemConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"element" (<a href="#prod-xquery-QName">QName</a> | ("{"
<a href="#doc-xquery-Expr">Expr</a> "}")) "{" <a href=
"#doc-xquery-ContentExpr">ContentExpr</a>? "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ContentExpr" id=
"doc-xquery-ContentExpr"></a>[112]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ContentExpr" class=
"xquery">ContentExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Expr">Expr</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-computed-elem-const" id="dt-computed-elem-const"
title="computed element constructor">Definition</a>: A <b>computed
element constructor</b> creates an element node, allowing both the
name and the content of the node to be computed.]</p>
<p>If the keyword <code>element</code> is followed by a QName, it
is expanded using the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>, and the
resulting <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> is used as the
<code>node-name</code> property of the constructed element node. If
expansion of the QName is not successful, a <a title="static error"
href="#dt-static-error">static error</a> is raised [<a href=
"#ERRXPST0081" title="err:XPST0081">err:XPST0081</a>].</p>
<p>If the keyword <code>element</code> is followed by a <a title=
"name expression" href="#dt-name-expression">name expression</a>,
the name expression is processed as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the value of the <a title="name expression" href=
"#dt-name-expression">name expression</a>. If the result of
atomization is not a single atomic value of type
<code>xs:QName</code>, <code>xs:string</code>, or
<code>xs:untypedAtomic</code>, a <a title="type error" href=
"#dt-type-error">type error</a> is raised [<a href="#ERRXPTY0004"
title="err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the atomized value of the <a title="name expression" href=
"#dt-name-expression">name expression</a> is of type
<code>xs:QName</code>, that <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> is used as the
<code>node-name</code> property of the constructed element,
retaining the prefix part of the QName.</p>
</li>
<li>
<p>If the atomized value of the <a title="name expression" href=
"#dt-name-expression">name expression</a> is of type
<code>xs:string</code> or <code>xs:untypedAtomic</code>, that value
is converted to an <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a>. If the string value
contains a namespace prefix, that prefix is resolved to a namespace
URI using the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>. If the
string value contains no namespace prefix, it is treated as a local
name in the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a>. The
resulting <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> is used as the
<code>node-name</code> property of the constructed element,
retaining the prefix part of the QName. If conversion of the
atomized <a title="name expression" href="#dt-name-expression">name
expression</a> to an expanded QName is not successful, a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a> is
raised [<a href="#ERRXQDY0074" title=
"err:XQDY0074">err:XQDY0074</a>].</p>
</li>
</ol>
<p>A <a title="dynamic error" href="#dt-dynamic-error">dynamic
error</a> is raised [<a href="#ERRXQDY0096" title=
"err:XQDY0096">err:XQDY0096</a>] if the node-name of the
constructed element node has any of the following properties:</p>
<ul>
<li>
<p>Its namespace prefix is <code>xmlns</code>.</p>
</li>
<li>
<p>Its namespace URI is
<code>http://www.w3.org/2000/xmlns/</code>.</p>
</li>
<li>
<p>Its namespace prefix is <code>xml</code> and its namespace URI
is not <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>Its namespace prefix is other than <code>xml</code> and its
namespace URI is
<code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
</ul>
<p>The <a title="content expression" href=
"#dt-content-expression">content expression</a> of a computed
element constructor (if present) is processed in exactly the same
way as an enclosed expression in the content of a <a title=
"direct element constructor" href="#dt-direct-elem-const">direct
element constructor</a>, as described in Step 1e of <a href=
"#id-content"><b>3.7.1.3 Content</b></a>. The result of processing
the content expression is a sequence of nodes called the <b>content
sequence</b>. If the <a title="content expression" href=
"#dt-content-expression">content expression</a> is absent, the
content sequence is an empty sequence.</p>
<p>Processing of the computed element constructor proceeds as
follows:</p>
<ol class="enumar">
<li>
<p>If the content sequence contains a document node, the document
node is replaced in the content sequence by its children.</p>
</li>
<li>
<p>Adjacent text nodes in the content sequence are merged into a
single text node by concatenating their contents, with no
intervening blanks. After concatenation, any text node whose
content is a zero-length string is deleted from the content
sequence.</p>
</li>
<li>
<p>If the content sequence contains an attribute node following a
node that is not an attribute node, a <a title="type error" href=
"#dt-type-error">type error</a> is raised [<a href="#ERRXQTY0024"
title="err:XQTY0024">err:XQTY0024</a>].</p>
</li>
<li>
<p>The properties of the newly constructed element node are
determined as follows:</p>
<ol class="enumla">
<li>
<p><code>node-name</code> is the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> resulting from processing
the specified QName or <a title="name expression" href=
"#dt-name-expression">name expression</a>, as described above.</p>
</li>
<li>
<p><code>parent</code> is empty.</p>
</li>
<li>
<p><code>attributes</code> consist of all the attribute nodes in
the content sequence, in <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> order.
Note that the <code>parent</code> property of each of these
attribute nodes has been set to the newly constructed element node.
If two or more attributes have the same <code>node-name</code>, a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
is raised [<a href="#ERRXQDY0025" title=
"err:XQDY0025">err:XQDY0025</a>]. If an attribute named
<code>xml:space</code> has a value other than <code>preserve</code>
or <code>default</code>, a dynamic error <a title="may" href=
"#may">MAY</a> be raised [<a href="#ERRXQDY0092" title=
"err:XQDY0092">err:XQDY0092</a>].</p>
</li>
<li>
<p><code>children</code> consist of all the element, text, comment,
and processing instruction nodes in the content sequence. Note that
the <code>parent</code> property of each of these nodes has been
set to the newly constructed element node.</p>
</li>
<li>
<p><code>base-uri</code> is set to the following value:</p>
<ol class="enumlr">
<li>
<p>If the constructed node has an attribute named
<code>xml:base</code>, then the value of this attribute, resolved
if it is relative against the <a title="base URI" href=
"#dt-base-uri">base URI</a> in the <a title="base URI" href=
"#dt-base-uri">static context</a>. The value of the
<code>xml:base</code> attribute is normalized as described in
<a href="#XMLBASE">[XML Base]</a>.</p>
</li>
<li>
<p>Otherwise, the value of the <a title="base URI" href=
"#dt-base-uri">base URI</a> in the <a title="base URI" href=
"#dt-base-uri">static context</a>.</p>
</li>
</ol>
</li>
<li>
<p><code>in-scope-namespaces</code> are computed as described in
<a href="#id-ns-nodes-on-elements"><b>3.7.4 In-scope Namespaces of
a Constructed Element</b></a>.</p>
</li>
<li>
<p>The <code>nilled</code> property is <code>false</code>.</p>
</li>
<li>
<p>The <code>string-value</code> property is equal to the
concatenated contents of the text-node descendants in document
order.</p>
</li>
<li>
<p>The <code>typed-value</code> property is equal to the
<code>string-value</code> property, as an instance of
<code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>If <a title="construction mode" href=
"#dt-construction-mode">construction mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a> is
<code>strip</code>, the <code>type-name</code> property is
<code>xs:untyped</code>. On the other hand, if construction mode is
<code>preserve</code>, the <code>type-name</code> property is
<code>xs:anyType</code>.</p>
</li>
<li>
<p>The <code>is-id</code> and <code>is-idrefs</code> properties are
set to <code>false</code>.</p>
</li>
</ol>
</li>
</ol>
<p>A computed element constructor might be used to make a modified
copy of an existing element. For example, if the variable
<code>$e</code> is bound to an element with <a title="numeric"
href="#dt-numeric">numeric</a> content, the following constructor
might be used to create a new element with the same name and
attributes as <code>$e</code> and with numeric content equal to
twice the value of <code>$e</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
element {fn:node-name($e)}
   {$e/@*, 2 * fn:data($e)}
</pre></div>
</div>
<p>In this example, if <code>$e</code> is bound by the expression
<code>let $e := &lt;length
units="inches"&gt;{5}&lt;/length&gt;</code>, then the result of the
example expression is the element <code>&lt;length
units="inches"&gt;10&lt;/length&gt;</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The <a title="static type" href="#dt-static-type">static
type</a> of the expression <code>fn:node-name($e)</code> is
<code>xs:QName?</code>, denoting zero or one QName. Therefore, if
the <a title="static typing feature" href=
"#dt-static-typing-feature">Static Typing Feature</a> is in effect,
the above example raises a static type error, since the name
expression in a computed element constructor is required to return
exactly one string or QName. In order to avoid the static type
error, the name expression <code>fn:node-name($e)</code> could be
rewritten as <code>fn:exactly-one(fn:node-name($e))</code>. If the
<a title="static typing feature" href=
"#dt-static-typing-feature">Static Typing Feature</a> is not in
effect, the example can be successfully evaluated as written,
provided that <code>$e</code> is bound to exactly one element node
with numeric content.</p>
</div>
<p>One important purpose of computed constructors is to allow the
name of a node to be computed. We will illustrate this feature by
an expression that translates the name of an element from one
language to another. Suppose that the variable <code>$dict</code>
is bound to a <code>dictionary</code> element containing a sequence
of <code>entry</code> elements, each of which encodes translations
for a specific word. Here is an example entry that encodes the
German and Italian variants of the word "address":</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;entry word="address"&gt;
   &lt;variant xml:lang="de"&gt;Adresse&lt;/variant&gt;
   &lt;variant xml:lang="it"&gt;indirizzo&lt;/variant&gt;
&lt;/entry&gt; 
</pre></div>
</div>
<p>Suppose further that the variable <code>$e</code> is bound to
the following element:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;address&gt;123 Roosevelt Ave. Flushing, NY 11368&lt;/address&gt;
</pre></div>
</div>
<p>Then the following expression generates a new element in which
the name of <code>$e</code> has been translated into Italian and
the content of <code>$e</code> (including its attributes, if any)
has been preserved. The first enclosed expression after the
<code>element</code> keyword generates the name of the element, and
the second enclosed expression generates the content and
attributes:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
  element 
    {$dict/entry[@word=name($e)]/variant[@xml:lang="it"]}
    {$e/@*, $e/node()}
</pre></div>
</div>
<p>The result of this expression is as follows:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;indirizzo&gt;123 Roosevelt Ave. Flushing, NY 11368&lt;/indirizzo&gt;
</pre></div>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>As in the previous example, if the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is in effect, the enclosed expression that
computes the element name in the above computed element constructor
must be wrapped in a call to the <code>fn:exactly-one</code>
function in order to avoid a static type error.</p>
</div>
<p>Additional examples of computed element constructors can be
found in <a href="#id-recursive-transformations"><b>I.4 Recursive
Transformations</b></a>.</p>
</div>
<div class="div4">
<h5><a name="id-computedAttributes" id=
"id-computedAttributes"></a>3.7.3.2 Computed Attribute
Constructors</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CompAttrConstructor" id=
"doc-xquery-CompAttrConstructor"></a>[113]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CompAttrConstructor" class=
"xquery">CompAttrConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"attribute" (<a href="#prod-xquery-QName">QName</a> |
("{" <a href="#doc-xquery-Expr">Expr</a> "}")) "{" <a href=
"#doc-xquery-Expr">Expr</a>? "}"</code></td>
</tr>
</tbody>
</table>
<p>A computed attribute constructor creates a new attribute node,
with its own node identity.</p>
<p>If the keyword <code>attribute</code> is followed by a QName,
that QName is expanded using the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>, and the
resulting <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (including its prefix) is
used as the <code>node-name</code> property of the constructed
attribute node. If expansion of the QName is not successful, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXPST0081" title=
"err:XPST0081">err:XPST0081</a>].</p>
<p>If the keyword <code>attribute</code> is followed by a <a title=
"name expression" href="#dt-name-expression">name expression</a>,
the name expression is processed as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the result of the <a title="name expression" href=
"#dt-name-expression">name expression</a>. If the result of
<a title="atomization" href="#dt-atomization">atomization</a> is
not a single atomic value of type <code>xs:QName</code>,
<code>xs:string</code>, or <code>xs:untypedAtomic</code>, a
<a title="type error" href="#dt-type-error">type error</a> is
raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the atomized value of the <a title="name expression" href=
"#dt-name-expression">name expression</a> is of type
<code>xs:QName</code>:</p>
<ol class="enumla">
<li>
<p>If the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> returned by the atomized
name expression has a namespace URI but has no prefix, it is given
an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
prefix.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>This step is necessary because attributes have no default
namespace. Therefore any attribute name that has a namespace URI
must also have a prefix.</p>
</div>
</li>
<li>
<p>The resulting <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (including its prefix) is
used as the <code>node-name</code> property of the constructed
attribute node.</p>
</li>
</ol>
</li>
<li>
<p>If the atomized value of the <a title="name expression" href=
"#dt-name-expression">name expression</a> is of type
<code>xs:string</code> or <code>xs:untypedAtomic</code>, that value
is converted to an <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a>. If the string value
contains a namespace prefix, that prefix is resolved to a namespace
URI using the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>. If the
string value contains no namespace prefix, it is treated as a local
name in no namespace. The resulting <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (including its prefix) is
used as the <code>node-name</code> property of the constructed
attribute. If conversion of the atomized <a title="name expression"
href="#dt-name-expression">name expression</a> to an <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a> is
not successful, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXQDY0074" title="err:XQDY0074">err:XQDY0074</a>].</p>
</li>
</ol>
<p>A <a title="static error" href="#dt-static-error">dynamic
error</a> is raised [<a href="#ERRXQDY0044" title=
"err:XQDY0044">err:XQDY0044</a>] if the node-name of the
constructed attribute node has any of the following properties:</p>
<ul>
<li>
<p>Its namespace prefix is <code>xmlns</code>.</p>
</li>
<li>
<p>It has no namespace prefix and its local name is
<code>xmlns</code>.</p>
</li>
<li>
<p>Its namespace URI is
<code>http://www.w3.org/2000/xmlns/</code>.</p>
</li>
<li>
<p>Its namespace prefix is <code>xml</code> and its namespace URI
is not <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>Its namespace prefix is other than <code>xml</code> and its
namespace URI is
<code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
</ul>
<p>The <a title="content expression" href=
"#dt-content-expression">content expression</a> of a computed
attribute constructor is processed as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the result of the <a title="content expression" href=
"#dt-content-expression">content expression</a>, converting it to a
sequence of atomic values. (If the <a title="content expression"
href="#dt-content-expression">content expression</a> is absent, the
result of this step is an empty sequence.)</p>
</li>
<li>
<p>If the result of atomization is an empty sequence, the value of
the attribute is the zero-length string. Otherwise, each atomic
value in the atomized sequence is cast into a string.</p>
</li>
<li>
<p>The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. The resulting string becomes the
<code>string-value</code> property of the new attribute node. The
<a title="type annotation" href="#dt-type-annotation">type
annotation</a> (<code>type-name</code> property) of the new
attribute node is <code>xs:untypedAtomic</code>. The
<code>typed-value</code> property of the attribute node is the same
as its <code>string-value</code>, as an instance of
<code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>The <code>parent</code> property of the attribute node is set to
empty.</p>
</li>
<li>
<p>If the attribute name is <code>xml:id</code>, then
<code>xml:id</code> processing is performed as defined in <a href=
"#XMLID">[XML ID]</a>. This ensures that the attribute node has the
type <code>xs:ID</code> and that its value is properly normalized.
If an error is encountered during <code>xml:id</code> processing,
an implementation <a title="may" href="#may">MAY</a> raise a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
[<a href="#ERRXQDY0091" title="err:XQDY0091">err:XQDY0091</a>].</p>
</li>
<li>
<p>If the attribute name is <code>xml:id</code>, the
<code>is-id</code> property of the resulting attribute node is set
to <code>true</code>; otherwise the <code>is-id</code> property is
set to <code>false</code>. The <code>is-idrefs</code> property of
the attribute node is unconditionally set to
<code>false</code>.</p>
</li>
<li>
<p>If the attribute name is <code>xml:space</code> and the
attribute value is other than <code>preserve</code> or
<code>default</code>, a dynamic error <a title="may" href=
"#may">MAY</a> be raised [<a href="#ERRXQDY0092" title=
"err:XQDY0092">err:XQDY0092</a>].</p>
</li>
</ol>
<ul>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
attribute size {4 + 3}
</pre></div>
</div>
<p>The <a title="string value" href="#dt-string-value">string
value</a> of the <code>size</code> attribute is "<code>7</code>"
and its type is <code>xs:untypedAtomic</code>.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
attribute
   { if ($sex = "M") then "husband" else "wife" }
   { &lt;a&gt;Hello&lt;/a&gt;, 1 to 3, &lt;b&gt;Goodbye&lt;/b&gt; }
</pre></div>
</div>
<p>The name of the constructed attribute is either
<code>husband</code> or <code>wife</code>. Its <a title=
"string value" href="#dt-string-value">string value</a> is
"<code>Hello 1 2 3 Goodbye</code>".</p>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="id-documentConstructors" id=
"id-documentConstructors"></a>3.7.3.3 Document Node
Constructors</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CompDocConstructor" id=
"doc-xquery-CompDocConstructor"></a>[110]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CompDocConstructor" class=
"xquery">CompDocConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"document" "{" <a href="#doc-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
</table>
<p>All document node constructors are computed constructors. The
result of a document node constructor is a new document node, with
its own node identity.</p>
<p>A document node constructor is useful when the result of a query
is to be a document in its own right. The following example
illustrates a query that returns an XML document containing a root
element named <code>author-list</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
document
   {
      &lt;author-list&gt;
         {fn:doc("bib.xml")/bib/book/author}
      &lt;/author-list&gt;
   }
</pre></div>
</div>
<p>The <a title="content expression" href=
"#dt-content-expression">content expression</a> of a document node
constructor is processed in exactly the same way as an enclosed
expression in the content of a <a title=
"direct element constructor" href="#dt-direct-elem-const">direct
element constructor</a>, as described in Step 1e of <a href=
"#id-content"><b>3.7.1.3 Content</b></a>. The result of processing
the content expression is a sequence of nodes called the <b>content
sequence</b>. Processing of the document node constructor then
proceeds as follows:</p>
<ol class="enumar">
<li>
<p>If the content sequence contains a document node, the document
node is replaced in the content sequence by its children.</p>
</li>
<li>
<p>Adjacent text nodes in the content sequence are merged into a
single text node by concatenating their contents, with no
intervening blanks. After concatenation, any text node whose
content is a zero-length string is deleted from the content
sequence.</p>
</li>
<li>
<p>If the content sequence contains an attribute node, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>The properties of the newly constructed document node are
determined as follows:</p>
<ol class="enumla">
<li>
<p><code>base-uri</code> is taken from <a title="base URI" href=
"#dt-base-uri">base URI</a> in the <a title="base URI" href=
"#dt-base-uri">static context</a>. If no base URI is defined in the
static context, the <code>base-uri</code> property is empty.</p>
</li>
<li>
<p><code>children</code> consist of all the element, text, comment,
and processing instruction nodes in the content sequence. Note that
the <code>parent</code> property of each of these nodes has been
set to the newly constructed document node.</p>
</li>
<li>
<p>The <code>unparsed-entities</code> and <code>document-uri</code>
properties are empty.</p>
</li>
<li>
<p>The <code>string-value</code> property is equal to the
concatenated contents of the text-node descendants in document
order.</p>
</li>
<li>
<p>The <code>typed-value</code> property is equal to the
<code>string-value</code> property, as an instance of
<code>xs:untypedAtomic</code>.</p>
</li>
</ol>
</li>
</ol>
<p>No validation is performed on the constructed document node. The
<a href="#XML">[XML 1.0]</a> rules that govern the structure of an
XML document (for example, the document node must have exactly one
child that is an element node) are not enforced by the XQuery
document node constructor.</p>
</div>
<div class="div4">
<h5><a name="id-textConstructors" id=
"id-textConstructors"></a>3.7.3.4 Text Node Constructors</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CompTextConstructor" id=
"doc-xquery-CompTextConstructor"></a>[114]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CompTextConstructor" class=
"xquery">CompTextConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"text" "{" <a href="#doc-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
</table>
<p>All text node constructors are computed constructors. The result
of a text node constructor is a new text node, with its own node
identity.</p>
<p>The <a title="content expression" href=
"#dt-content-expression">content expression</a> of a text node
constructor is processed as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the value of the <a title="content expression" href=
"#dt-content-expression">content expression</a>, converting it to a
sequence of atomic values.</p>
</li>
<li>
<p>If the result of atomization is an empty sequence, no text node
is constructed. Otherwise, each atomic value in the atomized
sequence is cast into a string.</p>
</li>
<li>
<p>The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. The resulting string becomes the
<code>content</code> property of the constructed text node.</p>
</li>
</ol>
<p>The <code>parent</code> property of the constructed text node is
set to empty.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>It is possible for a text node constructor to construct a text
node containing a zero-length string. However, if used in the
content of a constructed element or document node, such a text node
will be deleted or merged with another text node.</p>
</div>
<p>The following example illustrates a text node constructor:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
text {"Hello"}
</pre></div>
</div>
</div>
<div class="div4">
<h5><a name="id-computed-pis" id="id-computed-pis"></a>3.7.3.5
Computed Processing Instruction Constructors</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CompPIConstructor" id=
"doc-xquery-CompPIConstructor"></a>[116]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CompPIConstructor" class=
"xquery">CompPIConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"processing-instruction" (<a href=
"#prod-xquery-NCName">NCName</a> | ("{" <a href=
"#doc-xquery-Expr">Expr</a> "}")) "{" <a href=
"#doc-xquery-Expr">Expr</a>? "}"</code></td>
</tr>
</tbody>
</table>
<p>A computed processing instruction constructor (<a href=
"#doc-xquery-CompPIConstructor">CompPIConstructor</a>) constructs a
new processing instruction node with its own node identity.</p>
<p>If the keyword <code>processing-instruction</code> is followed
by an NCName, that NCName is used as the <code>target</code>
property of the constructed node. If the keyword
<code>processing-instruction</code> is followed by a <a title=
"name expression" href="#dt-name-expression">name expression</a>,
the name expression is processed as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the value of the <a title="name expression" href=
"#dt-name-expression">name expression</a>. If the result of
<a title="atomization" href="#dt-atomization">atomization</a> is
not a single atomic value of type <code>xs:NCName</code>,
<code>xs:string</code>, or <code>xs:untypedAtomic</code>, a
<a title="type error" href="#dt-type-error">type error</a> is
raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the atomized value of the <a title="name expression" href=
"#dt-name-expression">name expression</a> is of type
<code>xs:string</code> or <code>xs:untypedAtomic</code>, that value
is cast to the type <code>xs:NCName</code>. If the value cannot be
cast to <code>xs:NCName</code>, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXQDY0041" title="err:XQDY0041">err:XQDY0041</a>].</p>
</li>
<li>
<p>The resulting NCName is then used as the <code>target</code>
property of the newly constructed processing instruction node.
However, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised if the NCName is
equal to "<code>XML</code>" (in any combination of upper and lower
case) [<a href="#ERRXQDY0064" title=
"err:XQDY0064">err:XQDY0064</a>].</p>
</li>
</ol>
<p>The <a title="content expression" href=
"#dt-content-expression">content expression</a> of a computed
processing instruction constructor is processed as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the value of the <a title="content expression" href=
"#dt-content-expression">content expression</a>, converting it to a
sequence of atomic values. (If the <a title="content expression"
href="#dt-content-expression">content expression</a> is absent, the
result of this step is an empty sequence.)</p>
</li>
<li>
<p>If the result of atomization is an empty sequence, it is
replaced by a zero-length string. Otherwise, each atomic value in
the atomized sequence is cast into a string. If any of the
resulting strings contains the string "<code>?&gt;</code>", a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
[<a href="#ERRXQDY0026" title="err:XQDY0026">err:XQDY0026</a>] is
raised.</p>
</li>
<li>
<p>The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. Leading whitespace is removed
from the resulting string. The resulting string then becomes the
<code>content</code> property of the constructed processing
instruction node.</p>
</li>
</ol>
<p>The remaining properties of the new processing instruction node
are determined as follows:</p>
<ol class="enumar">
<li>
<p>The <code>parent</code> property is empty.</p>
</li>
<li>
<p>The <code>base-uri</code> property is empty.</p>
</li>
</ol>
<p>The following example illustrates a computed processing
instruction constructor:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $target := "audio-output",
    $content := "beep" 
return processing-instruction {$target} {$content}
</pre></div>
</div>
<p>The processing instruction node constructed by this example
might be serialized as follows:</p>
<div class="exampleInner">
<pre>
&lt;?audio-output beep?&gt;
</pre></div>
</div>
<div class="div4">
<h5><a name="id-computed-comments" id=
"id-computed-comments"></a>3.7.3.6 Computed Comment
Constructors</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CompCommentConstructor" id=
"doc-xquery-CompCommentConstructor"></a>[115]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CompCommentConstructor" class=
"xquery">CompCommentConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"comment" "{" <a href="#doc-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
</table>
<p>A computed comment constructor (<a href=
"#doc-xquery-CompCommentConstructor">CompCommentConstructor</a>)
constructs a new comment node with its own node identity. The
<a title="content expression" href="#dt-content-expression">content
expression</a> of a computed comment constructor is processed as
follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the value of the <a title="content expression" href=
"#dt-content-expression">content expression</a>, converting it to a
sequence of atomic values.</p>
</li>
<li>
<p>If the result of atomization is an empty sequence, it is
replaced by a zero-length string. Otherwise, each atomic value in
the atomized sequence is cast into a string.</p>
</li>
<li>
<p>The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. The resulting string becomes the
<code>content</code> property of the constructed comment node.</p>
</li>
<li>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> [<a href="#ERRXQDY0072"
title="err:XQDY0072">err:XQDY0072</a>] if the result of the
<a title="content expression" href="#dt-content-expression">content
expression</a> of a computed comment constructor contains two
adjacent hyphens or ends with a hyphen.</p>
</li>
</ol>
<p>The <code>parent</code> property of the constructed comment node
is set to empty.</p>
<p>The following example illustrates a computed comment
constructor:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $homebase := "Houston" 
return comment {fn:concat($homebase, ", we have a problem.")}
</pre></div>
</div>
<p>The comment node constructed by this example might be serialized
as follows:</p>
<div class="exampleInner">
<pre>
&lt;!--Houston, we have a problem.--&gt;
</pre></div>
</div>
</div>
<div class="div3">
<h4><a name="id-ns-nodes-on-elements" id=
"id-ns-nodes-on-elements"></a>3.7.4 In-scope Namespaces of a
Constructed Element</h4>
<p>An element node constructed by a direct or computed element
constructor has an <a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a> property that
consists of a set of <a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">namespace bindings</a>. The in-scope
namespaces of an element node may affect the way the node is
serialized (see <a href="#id-serialization"><b>2.2.4
Serialization</b></a>), and may also affect the behavior of certain
functions that operate on nodes, such as <code>fn:name</code>. Note
the difference between <a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a>, which is a
dynamic property of an element node, and <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>, which is a
static property of an expression. Also note that one of the
namespace bindings in the in-scope namespaces may have no prefix
(denoting the default namespace for the given element). The
in-scope namespaces of a constructed element node consist of the
following namespace bindings:</p>
<ul>
<li>
<p>A namespace binding is created for each namespace declared in
the current element constructor by a <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a>.</p>
</li>
<li>
<p>A namespace binding is created for each namespace that is
declared in a <a title="namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a> of an
enclosing <a title="direct element constructor" href=
"#dt-direct-elem-const">direct element constructor</a> and not
overridden by the current element constructor or an intermediate
constructor.</p>
</li>
<li>
<p>A namespace binding is always created to bind the prefix
<code>xml</code> to the namespace URI
<code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>For each namespace used in the name of the constructed element
or in the names of its attributes, a namespace binding must exist.
If a namespace binding does not already exist for one of these
namespaces, a new namespace binding is created for it. If the name
of the node includes a prefix, that prefix is used in the namespace
binding; if the name has no prefix, then a binding is created for
the empty prefix. If this would result in a conflict, because it
would require two different bindings of the same prefix, then the
prefix used in the node name is changed to an arbitrary <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> prefix
that does not cause such a conflict, and a namespace binding is
created for this new prefix.</p>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p><a title="copy-namespaces mode" href=
"#dt-copy-namespaces-mode">Copy-namespaces mode</a> does not affect
the namespace bindings of a newly constructed element node. It
applies only to existing nodes that are copied by a constructor
expression.</p>
</div>
<p>The following query serves as an example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare namespace p="http://example.com/ns/p";
declare namespace q="http://example.com/ns/q";
declare namespace f="http://example.com/ns/f";

&lt;p:a q:b="{f:func(2)}" xmlns:r="http://example.com/ns/r"/&gt;
</pre></div>
</div>
<p>The <a title="in-scope namespaces" href=
"#dt-in-scope-namespaces">in-scope namespaces</a> of the resulting
<code>p:a</code> element consists of the following <a title=
"in-scope namespaces" href="#dt-in-scope-namespaces">namespace
bindings</a>:</p>
<ul>
<li>
<p><code>p = "http://example.com/ns/p"</code></p>
</li>
<li>
<p><code>q = "http://example.com/ns/q"</code></p>
</li>
<li>
<p><code>r = "http://example.com/ns/r"</code></p>
</li>
<li>
<p><code>xml = "http://www.w3.org/XML/1998/namespace"</code></p>
</li>
</ul>
<p>The namespace bindings for <code>p</code> and <code>q</code> are
added to the result element because their respective namespaces are
used in the names of the element and its attributes. The namespace
binding <code>r="http://example.com/ns/r"</code> is added to the
in-scope namespaces of the constructed element because it is
defined by a <a title="namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a>, even
though it is not used in a name.</p>
<p>No namespace binding corresponding to
<code>f="http://example.com/ns/f"</code> is created, because the
namespace prefix <code>f</code> appears only in the query prolog
and is not used in an element or attribute name of the constructed
node. This namespace binding does not appear in the query result,
even though it is present in the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> and is
available for use during processing of the query.</p>
<p>Note that the following constructed element, if nested within a
<code>validate</code> expression, cannot be validated:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;p xsi:type="xs:integer"&gt;3&lt;/p&gt;
</pre></div>
</div>
<p>The constructed element will have namespace bindings for the
prefixes <code>xsi</code> (because it is used in a name) and
<code>xml</code> (because it is defined for every constructed
element node). During validation of the constructed element, the
validator will be unable to interpret the namespace prefix
<code>xs</code> because it is has no namespace binding. Validation
of this constructed element could be made possible by providing a
<a title="namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a>, as
in the following example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;p xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xsi:type="xs:integer"&gt;3&lt;/p&gt;
</pre></div>
</div>
</div>
</div>
</div>
<div class="xquery">
<div class="div2">
<h3><a name="id-flwor-expressions" id=
"id-flwor-expressions"></a>3.8 FLWOR Expressions</h3>
<p>XQuery provides a feature called a FLWOR expression that
supports iteration and binding of variables to intermediate
results. This kind of expression is often useful for computing
joins between two or more documents and for restructuring data. The
name FLWOR, pronounced "flower", is suggested by the keywords
<code>for</code>, <code>let</code>, <code>where</code>, <code>order
by</code>, and <code>return</code>.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-FLWORExpr" id=
"doc-xquery-FLWORExpr"></a>[33]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-FLWORExpr" class=
"xquery">FLWORExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#doc-xquery-ForClause">ForClause</a> | <a href=
"#doc-xquery-LetClause">LetClause</a>)+ <a href=
"#doc-xquery-WhereClause">WhereClause</a>? <a href=
"#doc-xquery-OrderByClause">OrderByClause</a>? "return" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ForClause" id=
"doc-xquery-ForClause"></a>[34]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ForClause" class=
"xquery">ForClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"for" "$" <a href="#doc-xquery-VarName">VarName</a>
<a href="#doc-xquery-TypeDeclaration">TypeDeclaration</a>? <a href=
"#doc-xquery-PositionalVar">PositionalVar</a>? "in" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a> ("," "$" <a href=
"#doc-xquery-VarName">VarName</a> <a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a>? <a href=
"#doc-xquery-PositionalVar">PositionalVar</a>? "in" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-LetClause" id=
"doc-xquery-LetClause"></a>[36]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-LetClause" class=
"xquery">LetClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"let" "$" <a href="#doc-xquery-VarName">VarName</a>
<a href="#doc-xquery-TypeDeclaration">TypeDeclaration</a>? ":="
<a href="#doc-xquery-ExprSingle">ExprSingle</a> ("," "$" <a href=
"#doc-xquery-VarName">VarName</a> <a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a>? ":=" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-TypeDeclaration" id=
"doc-xquery-TypeDeclaration"></a>[118]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TypeDeclaration" class=
"xquery">TypeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"as" <a href=
"#doc-xquery-SequenceType">SequenceType</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PositionalVar" id=
"doc-xquery-PositionalVar"></a>[35]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-PositionalVar" class=
"xquery">PositionalVar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"at" "$" <a href=
"#doc-xquery-VarName">VarName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-WhereClause" id=
"doc-xquery-WhereClause"></a>[37]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-WhereClause" class=
"xquery">WhereClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"where" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrderByClause" id=
"doc-xquery-OrderByClause"></a>[38]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderByClause" class=
"xquery">OrderByClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(("order" "by") | ("stable" "order" "by")) <a href=
"#doc-xquery-OrderSpecList">OrderSpecList</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrderSpecList" id=
"doc-xquery-OrderSpecList"></a>[39]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderSpecList" class=
"xquery">OrderSpecList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-OrderSpec">OrderSpec</a> (","
<a href="#doc-xquery-OrderSpec">OrderSpec</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrderSpec" id=
"doc-xquery-OrderSpec"></a>[40]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderSpec" class=
"xquery">OrderSpec</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ExprSingle">ExprSingle</a> <a href=
"#doc-xquery-OrderModifier">OrderModifier</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrderModifier" id=
"doc-xquery-OrderModifier"></a>[41]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderModifier" class=
"xquery">OrderModifier</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("ascending" | "descending")? ("empty" ("greatest" |
"least"))? ("collation" <a href=
"#doc-xquery-URILiteral">URILiteral</a>)?</code></td>
</tr>
</tbody>
</table>
<p>The <code>for</code> and <code>let</code> clauses in a FLWOR
expression generate an ordered sequence of tuples of bound
variables, called the <b>tuple stream</b>. The optional
<code>where</code> clause serves to filter the tuple stream,
retaining some tuples and discarding others. The optional
<code>order by</code> clause can be used to reorder the tuple
stream. The <code>return</code> clause constructs the result of the
FLWOR expression. The <code>return</code> clause is evaluated once
for every tuple in the tuple stream, after filtering by the
<code>where</code> clause, using the variable bindings in the
respective tuples. The result of the FLWOR expression is an ordered
sequence containing the results of these evaluations, concatenated
as if by the <a title="comma operator" href=
"#dt-comma-operator">comma operator</a>.</p>
<p>The following example of a FLWOR expression includes all of the
possible clauses. The <code>for</code> clause iterates over all the
departments in an input document, binding the variable
<code>$d</code> to each department number in turn. For each binding
of <code>$d</code>, the <code>let</code> clause binds variable
<code>$e</code> to all the employees in the given department,
selected from another input document. The result of the
<code>for</code> and <code>let</code> clauses is a tuple stream in
which each tuple contains a pair of bindings for <code>$d</code>
and <code>$e</code> (<code>$d</code> is bound to a department
number and <code>$e</code> is bound to a set of employees in that
department). The <code>where</code> clause filters the tuple stream
by keeping only those binding-pairs that represent departments
having at least ten employees. The <code>order by</code> clause
orders the surviving tuples in descending order by the average
salary of the employees in the department. The <code>return</code>
clause constructs a new <code>big-dept</code> element for each
surviving tuple, containing the department number, headcount, and
average salary.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">for $d in fn:doc("depts.xml")/depts/deptno
let $e := fn:doc("emps.xml")/emps/emp[deptno = $d]
where fn:count($e) &gt;= 10
order by fn:avg($e/salary) descending
return
   &lt;big-dept&gt;
      {
      $d,
      &lt;headcount&gt;{fn:count($e)}&lt;/headcount&gt;,
      &lt;avgsal&gt;{fn:avg($e/salary)}&lt;/avgsal&gt;
      }
   &lt;/big-dept&gt;</span></span>
</pre></div>
</div>
<p>The clauses in a FLWOR expression are described in more detail
below.</p>
<div class="div3">
<h4><a name="id-for-let" id="id-for-let"></a>3.8.1 For and Let
Clauses</h4>
<p>The purpose of the <code>for</code> and <code>let</code> clauses
in a FLWOR expression is to produce a tuple stream in which each
tuple consists of one or more bound variables.</p>
<p>The simplest example of a <code>for</code> clause contains one
variable and an associated expression. [<a name=
"dt-binding-sequence" id="dt-binding-sequence" title=
"binding sequence">Definition</a>: The value of the expression
associated with a variable in a <code>for</code> clause is called
the <b>binding sequence</b> for that variable.] The
<code>for</code> clause iterates over the items in the binding
sequence, binding the variable to each item in turn. If <a title=
"ordering mode" href="#dt-ordering-mode">ordering mode</a> is
<code>ordered</code>, the resulting sequence of variable bindings
is ordered according to the order of values in the binding
sequence; otherwise the ordering of the variable bindings is
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
<p>A <code>for</code> clause may also contain multiple variables,
each with an associated expression whose value is the binding
sequence for that variable. In this case, the <code>for</code>
clause iterates each variable over its binding sequence. The
resulting tuple stream contains one tuple for each combination of
values in the respective binding sequences. If <a title=
"ordering mode" href="#dt-ordering-mode">ordering mode</a> is
<code>ordered</code>, the order of the tuple stream is determined
primarily by the order of the binding sequence of the leftmost
variable, and secondarily by the binding sequences of the other
variables, working from left to right. Otherwise, the ordering of
the variable bindings is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
<p>A <code>let</code> clause may also contain one or more
variables, each with an associated expression. Unlike a
<code>for</code> clause, however, a <code>let</code> clause binds
each variable to the result of its associated expression, without
iteration. The variable bindings generated by <code>let</code>
clauses are added to the binding tuples generated by the
<code>for</code> clauses. If there are no <code>for</code> clauses,
the <code>let</code> clauses generate one tuple containing all the
variable bindings.</p>
<p>Although <code>for</code> and <code>let</code> clauses both bind
variables, the manner in which variables are bound is quite
different, as illustrated by the following examples. The first
example uses a <code>let</code> clause:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">let $s := (&lt;one/&gt;, &lt;two/&gt;, &lt;three/&gt;)
return &lt;out&gt;{$s}&lt;/out&gt;</span></span>
</pre></div>
</div>
<p>The variable <code>$s</code> is bound to the result of the
expression <code>(&lt;one/&gt;, &lt;two/&gt;,
&lt;three/&gt;)</code>. Since there are no <code>for</code>
clauses, the <code>let</code> clause generates one tuple that
contains the binding of <code>$s</code>. The <code>return</code>
clause is invoked for this tuple, creating the following
output:</p>
<div class="exampleInner">
<pre>
&lt;out&gt;
   &lt;one/&gt;
   &lt;two/&gt;
   &lt;three/&gt;
&lt;/out&gt;
</pre></div>
<p>The next example is a similar query that contains a
<code>for</code> clause instead of a <code>let</code> clause:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">for $s in (&lt;one/&gt;, &lt;two/&gt;, &lt;three/&gt;)
return &lt;out&gt;{$s}&lt;/out&gt;</span></span>
</pre></div>
</div>
<p>In this example, the variable <code>$s</code> iterates over the
given expression. If <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is <code>ordered</code>,
<code>$s</code> is first bound to <code>&lt;one/&gt;</code>, then
to <code>&lt;two/&gt;</code>, and finally to
<code>&lt;three/&gt;</code>. One tuple is generated for each of
these bindings, and the <code>return</code> clause is invoked for
each tuple, creating the following output:</p>
<div class="exampleInner">
<pre>
&lt;out&gt;
   &lt;one/&gt;
&lt;/out&gt;
&lt;out&gt;
   &lt;two/&gt;
&lt;/out&gt;
&lt;out&gt;
   &lt;three/&gt;
&lt;/out&gt;
</pre></div>
<p>The following example illustrates how binding tuples are
generated by a <code>for</code> clause that contains multiple
variables when <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> is <code>ordered</code>.</p>
<div class="exampleInner">
<pre>
for $i in (1, 2), $j in (3, 4)
</pre></div>
<p>The tuple stream generated by the above <code>for</code> clause
is as follows:</p>
<div class="exampleInner">
<pre>
($i = 1, $j = 3)
($i = 1, $j = 4)
($i = 2, $j = 3)
($i = 2, $j = 4)
</pre></div>
<p>If <a title="ordering mode" href="#dt-ordering-mode">ordering
mode</a> were <code>unordered</code>, the <code>for</code> clause
in the above example would generate the same tuple stream but the
order of the tuples would be <a title="implementation dependent"
href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
<p>The scope of a variable bound in a <code>for</code> or
<code>let</code> clause comprises all subexpressions of the
containing FLWOR expression that appear after the variable binding.
The scope does not include the expression to which the variable is
bound. The following example illustrates how bindings in
<code>for</code> and <code>let</code> clauses may reference
variables that were bound in earlier clauses, or in earlier
bindings in the same clause of the FLWOR expression:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
for $x in $w, $a in f($x)
let $y := g($a)
for $z in p($x, $y)
return q($x, $y, $z)
</pre></div>
</div>
<p>The <code>for</code> and <code>let</code> clauses of a given
FLWOR expression may bind the same variable name more than once. In
this case, each new binding occludes the previous one, which
becomes inaccessible in the remainder of the FLWOR expression.</p>
<p>Each variable bound in a <code>for</code> or <code>let</code>
clause may have an optional <b>type declaration</b>, which is a
type declared using the syntax in <a href=
"#id-sequencetype-syntax"><b>2.5.3 SequenceType Syntax</b></a>. If
the type of a value bound to the variable does not match the
declared type according to the rules for <a title=
"SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. For
example, the following expression raises a <a title="type error"
href="#dt-type-error">type error</a> because the variable
<code>$salary</code> has a type declaration that is not satisfied
by the value that is bound to the variable:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $salary as xs:decimal :=  "cat"
return $salary * 2
</pre></div>
</div>
<p>Each variable bound in a <code>for</code> clause may have an
associated <b>positional variable</b> that is bound at the same
time. The name of the positional variable is preceded by the
keyword <code>at</code>. The positional variable always has an
implied type of <code>xs:integer</code>. As a variable iterates
over the items in its <a title="binding sequence" href=
"#dt-binding-sequence">binding sequence</a>, its positional
variable iterates over the integers that represent the ordinal
positions of those items in the binding sequence, starting with 1.
The expanded QName of a positional variable must be distinct from
the expanded QName of the variable with which it is associated
[<a href="#ERRXQST0089" title="err:XQST0089">err:XQST0089</a>].</p>
<p>Positional variables are illustrated by the following
<code>for</code> clause:</p>
<div class="exampleInner">
<pre>
for $car at $i in ("Ford", "Chevy"),
    $pet at $j in ("Cat", "Dog")
</pre></div>
<p>If <a title="ordering mode" href="#dt-ordering-mode">ordering
mode</a> is <code>ordered</code>, the tuple stream generated by the
above <code>for</code> clause is as follows:</p>
<div class="exampleInner">
<pre>
($i = 1, $car = "Ford", $j = 1, $pet = "Cat")
($i = 1, $car = "Ford", $j = 2, $pet = "Dog")
($i = 2, $car = "Chevy", $j = 1, $pet = "Cat")
($i = 2, $car = "Chevy", $j = 2, $pet = "Dog")
</pre></div>
<p>If <a title="ordering mode" href="#dt-ordering-mode">ordering
mode</a> is <code>unordered</code>, the order of the tuple stream
is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>. In
addition, if a <code>for</code> clause contains subexpressions that
are affected by <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a>, the association of
positional variables with items returned by these subexpressions is
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> if
<a title="ordering mode" href="#dt-ordering-mode">ordering mode</a>
is <code>unordered</code>.</p>
</div>
<div class="div3">
<h4><a name="id-where" id="id-where"></a>3.8.2 Where Clause</h4>
<p>The optional <code>where</code> clause serves as a filter for
the tuples of variable bindings generated by the <code>for</code>
and <code>let</code> clauses. The expression in the
<code>where</code> clause, called the <b>where-expression</b>, is
evaluated once for each of these tuples. If the <a title=
"effective boolean value" href="#dt-ebv">effective boolean
value</a> of the where-expression is <code>true</code>, the tuple
is retained and its variable bindings are used in an execution of
the <code>return</code> clause. If the <a title=
"effective boolean value" href="#dt-ebv">effective boolean
value</a> of the where-expression is <code>false</code>, the tuple
is discarded. The <a title="effective boolean value" href=
"#dt-ebv">effective boolean value</a> of an expression is defined
in <a href="#id-ebv"><b>2.4.3 Effective Boolean Value</b></a>.</p>
<p>The following expression illustrates how a <code>where</code>
clause might be applied to a <b>positional variable</b> in order to
perform sampling on an input sequence. This expression approximates
the average value in a sequence by sampling one value out of each
one hundred input values.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">fn:avg(for $x at $i in $inputvalues
    where $i mod 100 = 0   
    return $x)</span></span>
</pre></div>
</div>
</div>
<div class="div3">
<h4><a name="id-orderby-return" id="id-orderby-return"></a>3.8.3
Order By and Return Clauses</h4>
<p>The <code>return</code> clause of a FLWOR expression is
evaluated once for each tuple in the tuple stream, and the results
of these evaluations are concatenated, as if by the <a title=
"comma operator" href="#dt-comma-operator">comma operator</a>, to
form the result of the FLWOR expression.</p>
<p>If no <code>order by</code> clause is present, the order of the
tuple stream is determined by the <code>for</code> and
<code>let</code> clauses and by <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a>. If an <code>order by</code>
clause is present, it reorders the tuples in the tuple stream into
a new, value-based order. In either case, the resulting order
determines the order in which the <code>return</code> clause is
evaluated, once for each tuple, using the variable bindings in the
respective tuples. Note that <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> has no effect on a FLWOR
expression if an <code>order by</code> clause is present, since
<code>order by</code> takes precedence over <a title=
"ordering mode" href="#dt-ordering-mode">ordering mode</a>.</p>
<p>An <code>order by</code> clause contains one or more ordering
specifications, called <a href=
"#doc-xquery-OrderSpec">orderspecs</a>, as shown in the grammar
above. For each tuple in the tuple stream, after filtering by the
<code>where</code> clause, the orderspecs are evaluated, using the
variable bindings in that tuple. The relative order of two tuples
is determined by comparing the values of their orderspecs, working
from left to right until a pair of unequal values is encountered.
If an orderspec specifies a <a title="collation" href=
"#dt-collation">collation</a>, that collation is used in comparing
values of type <code>xs:string</code>, <code>xs:anyURI</code>, or
types derived from them (otherwise, the <a title=
"default collation" href="#dt-def-collation">default collation</a>
is used). If an orderspec specifies a collation by a relative URI,
that relative URI is resolved to an absolute URI using the
<a title="base URI" href="#dt-base-uri">base URI</a> in the
<a title="static context" href="#dt-static-context">static
context</a>. If an orderspec specifies a collation that is not
found in <a title="statically known collations" href=
"#dt-static-collations">statically known collations</a>, an error
is raised [<a href="#ERRXQST0076" title=
"err:XQST0076">err:XQST0076</a>].</p>
<p>The process of evaluating and comparing the orderspecs is based
on the following rules:</p>
<ul>
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
applied to the result of the expression in each orderspec. If the
result of atomization is neither a single atomic value nor an empty
sequence, a <a title="type error" href="#dt-type-error">type
error</a> is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the value of an orderspec has the <a title="dynamic type"
href="#dt-dynamic-type">dynamic type</a>
<code>xs:untypedAtomic</code> (such as character data in a
schemaless document), it is cast to the type
<code>xs:string</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Consistently treating untyped values as strings enables the
sorting process to begin without complete knowledge of the types of
all the values to be sorted.</p>
</div>
</li>
<li>
<p>All the non-empty orderspec values must be convertible to a
common type by <a title="subtype substitution" href=
"#dt-subtype-substitution">subtype substitution</a> and/or
<a title="type promotion" href="#dt-type-promotion">type
promotion</a>. The ordering is performed in the least common type
that has a <code>gt</code> operator. If two or more non-empty
orderspec values are not convertible to a common type that has a
<code>gt</code> operator, a <a title="type error" href=
"#dt-type-error">type error</a> is raised [<a href="#ERRXPTY0004"
title="err:XPTY0004">err:XPTY0004</a>].</p>
<ul>
<li>
<p>Example: The orderspec values include a value of type
<code>hatsize</code>, which is derived from
<code>xs:integer</code>, and a value of type <code>shoesize</code>,
which is derived from <code>xs:decimal</code>. The least common
type reachable by subtype substitution and type promotion is
<code>xs:decimal</code>.</p>
</li>
<li>
<p>Example: The orderspec values include a value of type
<code>xs:string</code> and a value of type <code>xs:anyURI</code>.
The least common type reachable by subtype substitution and type
promotion is <code>xs:string</code>.</p>
</li>
</ul>
</li>
</ul>
<p>For the purpose of determining their relative position in the
ordering sequence, the <em>greater-than</em> relationship between
two orderspec values <em>W</em> and <em>V</em> is defined as
follows:</p>
<ul>
<li>
<p>When the orderspec specifies <code>empty least</code>, the
following rules are applied in order:</p>
<ol class="enumar">
<li>
<p>If <em>V</em> is an empty sequence and <em>W</em> is not an
empty sequence, then <em>W</em> <em>greater-than</em> <em>V</em> is
true.</p>
</li>
<li>
<p>If <em>V</em> is <code>NaN</code> and <em>W</em> is neither
<code>NaN</code> nor an empty sequence, then <em>W</em>
<em>greater-than</em> <em>V</em> is true.</p>
</li>
<li>
<p>If a specific collation <em>C</em> is specified, and <em>V</em>
and <em>W</em> are both of type <code>xs:string</code> or are
convertible to <code>xs:string</code> by <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a> and/or <a title="type promotion" href=
"#dt-type-promotion">type promotion</a>, then:</p>
<p>If <code>fn:compare(V, W, C)</code> is less than zero, then
<em>W</em> <em>greater-than</em> <em>V</em> is true; otherwise
<em>W</em> <em>greater-than</em> <em>V</em> is false.</p>
</li>
<li>
<p>If none of the above rules apply, then:</p>
<p>If <code>W gt V</code> is true, then <em>W</em>
<em>greater-than</em> <em>V</em> is true; otherwise <em>W</em>
<em>greater-than</em> <em>V</em> is false.</p>
</li>
</ol>
</li>
<li>
<p>When the orderspec specifies <code>empty greatest</code>, the
following rules are applied in order:</p>
<ol class="enumar">
<li>
<p>If <em>W</em> is an empty sequence and <em>V</em> is not an
empty sequence, then <em>W</em> <em>greater-than</em> <em>V</em> is
true.</p>
</li>
<li>
<p>If <em>W</em> is <code>NaN</code> and <em>V</em> is neither
<code>NaN</code> nor an empty sequence, then <em>W</em>
<em>greater-than</em> <em>V</em> is true.</p>
</li>
<li>
<p>If a specific collation <em>C</em> is specified, and <em>V</em>
and <em>W</em> are both of type <code>xs:string</code> or are
convertible to <code>xs:string</code> by <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a> and/or <a title="type promotion" href=
"#dt-type-promotion">type promotion</a>, then:</p>
<p>If <code>fn:compare(V, W, C)</code> is less than zero, then
<em>W</em> <em>greater-than</em> <em>V</em> is true; otherwise
<em>W</em> <em>greater-than</em> <em>V</em> is false.</p>
</li>
<li>
<p>If none of the above rules apply, then:</p>
<p>If <code>W gt V</code> is true, then <em>W</em>
<em>greater-than</em> <em>V</em> is true; otherwise <em>W</em>
<em>greater-than</em> <em>V</em> is false.</p>
</li>
</ol>
</li>
<li>
<p>When the orderspec specifies neither <code>empty least</code>
nor <code>empty greatest</code>, the <a title=
"default order for empty sequences" href=
"#dt-default-empty-order">default order for empty sequences</a> in
the <a title="static context" href="#dt-static-context">static
context</a> determines whether the rules for <code>empty
least</code> or <code>empty greatest</code> are used.</p>
</li>
</ul>
<p>If T1 and T2 are two tuples in the tuple stream, and V1 and V2
are the first pair of values encountered when evaluating their
orderspecs from left to right for which one value is
<em>greater-than</em> the other (as defined above), then:</p>
<ol class="enumar">
<li>
<p>If V1 is <em>greater-than</em> V2: If the orderspec specifies
<code>descending</code>, then T1 precedes T2 in the tuple stream;
otherwise, T2 precedes T1 in the tuple stream.</p>
</li>
<li>
<p>If V2 is <em>greater-than</em> V1: If the orderspec specifies
<code>descending</code>, then T2 precedes T1 in the tuple stream;
otherwise, T1 precedes T2 in the tuple stream.</p>
</li>
</ol>
<p>If neither V1 nor V2 is <em>greater-than</em> the other for any
pair of orderspecs for tuples T1 and T2, the following rules
apply.</p>
<ol class="enumar">
<li>
<p>If <code>stable</code> is specified, the original order of T1
and T2 is preserved in the tuple stream.</p>
</li>
<li>
<p>If <code>stable</code> is not specified, the order of T1 and T2
in the tuple stream is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>If two orderspecs return the special floating-point values
positive and negative zero, neither of these values is
<em>greater-than</em> the other, since <code>+0.0 gt -0.0</code>
and <code>-0.0 gt +0.0</code> are both <code>false</code>.</p>
</div>
<p>An <code>order by</code> clause makes it easy to sort the result
of a FLWOR expression, even if the sort key is not included in the
result of the expression. For example, the following expression
returns employee names in descending order by salary, without
returning the actual salaries:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">for $e in $employees 
order by $e/salary descending 
return $e/name</span></span>
</pre></div>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Since the <code>order by</code> clause in a FLWOR expression is
the only facility provided by XQuery for specifying a value
ordering, a FLWOR expression must be used in some queries where
iteration would not otherwise be necessary. For example, a list of
books with price less than 100 might be obtained by a simple
<a title="path expression" href="#dt-path-expression">path
expression</a> such as <code>$books/book[price &lt; 100]</code>.
But if these books are to be returned in alphabetic order by title,
the query must be expressed as follows:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">for $b in $books/book[price &lt; 100]
order by $b/title
return $b</span></span>
</pre></div>
</div>
</div>
<p>The following example illustrates an <code>order by</code>
clause that uses several options. It causes a collection of books
to be sorted in primary order by title, and in secondary descending
order by price. A specific <a title="collation" href=
"#dt-collation">collation</a> is specified for the title ordering,
and in the ordering by price, books with no price are specified to
occur last (as though they have the least possible price). Whenever
two books with the same title and price occur, the keyword
<code>stable</code> indicates that their input order is
preserved.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">for $b in $books/book
stable order by $b/title 
      collation "http://www.example.org/collations/fr-ca",
   $b/price descending empty least
return $b</span></span>
</pre></div>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Parentheses are helpful in <code>return</code> clauses that
contain comma operators, since FLWOR expressions have a higher
precedence than the comma operator. For instance, the following
query raises an error because after the comma, <code>$j</code> is
no longer within the FLWOR expression, and is an <a title=
"undefined" href="#dt-undefined">undefined</a> variable:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $i := 5,
    $j := 20 * $i
return $i, $j
</pre></div>
</div>
<p>Parentheses can be used to bring <code>$j</code> into the
<code>return</code> clause of the FLWOR expression, as the
programmer probably intended:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $i := 5,
    $j := 20 * $i
return ($i, $j)
</pre></div>
</div>
</div>
</div>
<div class="div3">
<h4><a name="id-flwor-example" id="id-flwor-example"></a>3.8.4
Example</h4>
<p>The following example illustrates how FLWOR expressions can be
nested, and how ordering can be specified at multiple levels of an
element hierarchy. The example query inverts a document hierarchy
to transform a bibliography into an author list. The input (bound
to the variable <code>$bib</code>) is a <code>bib</code> element
containing a list of books, each of which in turn contains a list
of authors. The example is based on the following input:</p>
<div class="exampleInner">
<pre>
&lt;bib&gt;
  &lt;book&gt;
    &lt;title&gt;TCP/IP Illustrated&lt;/title&gt;
    &lt;author&gt;Stevens&lt;/author&gt;
    &lt;publisher&gt;Addison-Wesley&lt;/publisher&gt;
  &lt;/book&gt;
  &lt;book&gt;
    &lt;title&gt;Advanced Programming
           in the Unix Environment&lt;/title&gt;
    &lt;author&gt;Stevens&lt;/author&gt;
    &lt;publisher&gt;Addison-Wesley&lt;/publisher&gt;
  &lt;/book&gt;
  &lt;book&gt;
    &lt;title&gt;Data on the Web&lt;/title&gt;
    &lt;author&gt;Abiteboul&lt;/author&gt;
    &lt;author&gt;Buneman&lt;/author&gt;
    &lt;author&gt;Suciu&lt;/author&gt;
  &lt;/book&gt;
&lt;/bib&gt;
</pre></div>
<p>The following query transforms the input document into a list in
which each author's name appears only once, followed by a list of
titles of books written by that author. The
<code>fn:distinct-values</code> function is used to eliminate
duplicates (by value) from a list of author nodes. The author list,
and the lists of books published by each author, are returned in
alphabetic order using the <a title="default collation" href=
"#dt-def-collation">default collation</a>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class="parse-test">&lt;authlist&gt;
 {
   for $a in fn:distinct-values($bib/book/author)
   order by $a
   return
     &lt;author&gt;
        &lt;name&gt; {$a} &lt;/name&gt;
        &lt;books&gt;
          {
            for $b in $bib/book[author = $a]
            order by $b/title
            return $b/title 
          }
        &lt;/books&gt;
     &lt;/author&gt;
 }
&lt;/authlist&gt;</span></span>
</pre></div>
</div>
<p>The result of the above expression is as follows:</p>
<div class="exampleInner">
<pre>
&lt;authlist&gt;
   &lt;author&gt;
      &lt;name&gt;Abiteboul&lt;/name&gt;
      &lt;books&gt;
         &lt;title&gt;Data on the Web&lt;/title&gt;
      &lt;/books&gt;
   &lt;/author&gt;
   &lt;author&gt;
      &lt;name&gt;Buneman&lt;/name&gt;
      &lt;books&gt;
         &lt;title&gt;Data on the Web&lt;/title&gt;
      &lt;/books&gt;
   &lt;/author&gt;
   &lt;author&gt;
      &lt;name&gt;Stevens&lt;/name&gt;
      &lt;books&gt;
         &lt;title&gt;Advanced Programming
                in the Unix Environment&lt;/title&gt;
         &lt;title&gt;TCP/IP Illustrated&lt;/title&gt;
      &lt;/books&gt;
   &lt;/author&gt;
   &lt;author&gt;
      &lt;name&gt;Suciu&lt;/name&gt;
      &lt;books&gt;
         &lt;title&gt;Data on the Web&lt;/title&gt;
      &lt;/books&gt;
   &lt;/author&gt;
&lt;/authlist&gt;
</pre></div>
</div>
</div>
</div>
<div class="xquery">
<div class="div2">
<h3><a name="id-unordered-expressions" id=
"id-unordered-expressions"></a>3.9 Ordered and Unordered
Expressions</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrderedExpr" id=
"doc-xquery-OrderedExpr"></a>[91]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderedExpr" class=
"xquery">OrderedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"ordered" "{" <a href="#doc-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-UnorderedExpr" id=
"doc-xquery-UnorderedExpr"></a>[92]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-UnorderedExpr" class=
"xquery">UnorderedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"unordered" "{" <a href="#doc-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
</table>
<p>The purpose of <code>ordered</code> and <code>unordered</code>
expressions is to set the <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a> to
<code>ordered</code> or <code>unordered</code> for a certain region
in a query. The specified ordering mode applies to the expression
nested inside the curly braces. For expressions where the ordering
of the result is not significant, a performance advantage may be
realized by setting the ordering mode to <code>unordered</code>,
thereby granting the system flexibility to return the result in the
order that it finds most efficient.</p>
<p><a title="ordering mode" href="#dt-ordering-mode">Ordering
mode</a> affects the behavior of <a title="path expression" href=
"#dt-path-expression">path expressions</a> that include a
"<code>/</code>" or "<code>//</code>" operator or an <a title=
"axis step" href="#dt-axis-step">axis step</a>; <code>union</code>,
<code>intersect</code>, and <code>except</code> expressions; the
<code>fn:id</code> and <code>fn:idref</code> functions; and FLWOR
expressions that have no <code>order by</code> clause. If ordering
mode is <code>ordered</code>, node sequences returned by path
expressions, <code>union</code>, <code>intersect</code>, and
<code>except</code> expressions, and the <code>fn:id</code> and
<code>fn:idref</code> functions are in <a title="document order"
href="#dt-document-order">document order</a>; otherwise the order
of these return sequences is <a title="implementation dependent"
href="#dt-implementation-dependent">implementation-dependent</a>.
The effect of ordering mode on FLWOR expressions is described in
<a href="#id-flwor-expressions"><b>3.8 FLWOR Expressions</b></a>.
Ordering mode has no effect on duplicate elimination.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>In a region of a query where ordering mode is
<code>unordered</code>, the result of an expression may be
nondeterministic if the expression invokes certain functions that
are affected by the ordering of node sequences. These functions
include <code>fn:position</code>, <code>fn:last</code>,
<code>fn:index-of</code>, <code>fn:insert-before</code>,
<code>fn:remove</code>, <code>fn:reverse</code>, and
<code>fn:subsequence</code>. Also, within a <a title=
"path expression" href="#dt-path-expression">path expression</a> in
an unordered region, <a title="numeric predicate" href=
"#dt-numeric-predicate">numeric predicates</a> are
nondeterministic. For example, in an ordered region, the path
expression <code>(//a/b)[5]</code> will return the fifth qualifying
<code>b</code>-element in <a title="document order" href=
"#dt-document-order">document order</a>. In an unordered region,
the same expression will return an <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
qualifying <code>b</code>-element.</p>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The <code>fn:id</code> and <code>fn:idref</code> functions are
described in <a href="#FunctionsAndOperators">[XQuery 1.0 and XPath
2.0 Functions and Operators (Second Edition)]</a> as returning
their results in <a title="document order" href=
"#dt-document-order">document order</a>. Since ordering mode is a
feature of XQuery, relaxation of the ordering requirement for
function results when ordering mode is <code>unordered</code> is a
feature of XQuery rather than of the functions themselves.</p>
</div>
<p>The use of an <code>unordered</code> expression is illustrated
by the following example, which joins together two documents named
<code>parts.xml</code> and <code>suppliers.xml</code>. The example
returns the part numbers of red parts, paired with the supplier
numbers of suppliers who supply these parts. If an
<code>unordered</code> expression were not used, the resulting list
of (part number, supplier number) pairs would be required to have
an ordering that is controlled primarily by the <a title=
"document order" href="#dt-document-order">document order</a> of
<code>parts.xml</code> and secondarily by the <a title=
"document order" href="#dt-document-order">document order</a> of
<code>suppliers.xml</code>. However, this might not be the most
efficient way to process the query if the ordering of the result is
not important. An XQuery implementation might be able to process
the query more efficiently by using an index to find the red parts,
or by using <code>suppliers.xml</code> rather than
<code>parts.xml</code> to control the primary ordering of the
result. The <code>unordered</code> expression gives the query
evaluator freedom to make these kinds of optimizations.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class="parse-test">unordered {
  for $p in fn:doc("parts.xml")/parts/part[color = "Red"],
      $s in fn:doc("suppliers.xml")/suppliers/supplier
  where $p/suppno = $s/suppno  
  return
    &lt;ps&gt;
       { $p/partno, $s/suppno }
    &lt;/ps&gt;
}</span></span>
</pre></div>
</div>
<p>In addition to <code>ordered</code> and <code>unordered</code>
expressions, XQuery provides a function named
<code>fn:unordered</code> that operates on any sequence of items
and returns the same sequence in a nondeterministic order. A call
to the <code>fn:unordered</code> function may be thought of as
giving permission for the argument expression to be materialized in
whatever order the system finds most efficient. The
<code>fn:unordered</code> function relaxes ordering only for the
sequence that is its immediate operand, whereas an
<code>unordered</code> expression sets the <a title="ordering mode"
href="#dt-ordering-mode">ordering mode</a> for its operand
expression and all nested expressions.</p>
</div>
</div>
<div class="div2">
<h3><a name="id-conditionals" id="id-conditionals"></a>3.10
Conditional Expressions</h3>
<p>XQuery supports a conditional expression based on the keywords
<code>if</code>, <code>then</code>, and <code>else</code>.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-IfExpr" id=
"doc-xquery-IfExpr"></a>[45]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-IfExpr">IfExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"if" "(" <a href="#doc-xquery-Expr">Expr</a> ")" "then"
<a href="#doc-xquery-ExprSingle">ExprSingle</a> "else" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
</table>
<p>The expression following the <code>if</code> keyword is called
the <b>test expression</b>, and the expressions following the
<code>then</code> and <code>else</code> keywords are called the
<b>then-expression</b> and <b>else-expression</b>,
respectively.</p>
<p>The first step in processing a conditional expression is to find
the <a title="effective boolean value" href="#dt-ebv">effective
boolean value</a> of the test expression, as defined in <a href=
"#id-ebv"><b>2.4.3 Effective Boolean Value</b></a>.</p>
<p>The value of a conditional expression is defined as follows: If
the effective boolean value of the test expression is
<code>true</code>, the value of the then-expression is returned. If
the effective boolean value of the test expression is
<code>false</code>, the value of the else-expression is
returned.</p>
<p>Conditional expressions have a special rule for propagating
<a title="dynamic error" href="#dt-dynamic-error">dynamic
errors</a>. If the effective value of the test expression is
<code>true</code>, the conditional expression ignores (does not
raise) any dynamic errors encountered in the else-expression. In
this case, since the else-expression can have no observable effect,
it need not be evaluated. Similarly, if the effective value of the
test expression is <code>false</code>, the conditional expression
ignores any <a title="dynamic error" href=
"#dt-dynamic-error">dynamic errors</a> encountered in the
then-expression, and the then-expression need not be evaluated.</p>
<p>Here are some examples of conditional expressions:</p>
<ul>
<li>
<p>In this example, the test expression is a comparison
expression:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
if ($widget1/unit-cost &lt; $widget2/unit-cost) 
  then $widget1
  else $widget2
</pre></div>
</div>
</li>
<li>
<p>In this example, the test expression tests for the existence of
an attribute named <code>discounted</code>, independently of its
value:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
if ($part/@discounted) 
  then $part/wholesale 
  else $part/retail
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div2">
<h3><a name="id-quantified-expressions" id=
"id-quantified-expressions"></a>3.11 Quantified Expressions</h3>
<p>Quantified expressions support existential and universal
quantification. The value of a quantified expression is always
<code>true</code> or <code>false</code>.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-QuantifiedExpr" id=
"doc-xquery-QuantifiedExpr"></a>[42]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-QuantifiedExpr">QuantifiedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("some" | "every") "$" <a href=
"#doc-xquery-VarName">VarName</a> <a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a>? "in" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a> ("," "$" <a href=
"#doc-xquery-VarName">VarName</a> <a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a>? "in" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>)* "satisfies" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e14410.doc-xquery-TypeDeclaration" id=
"noid_d2e14410.doc-xquery-TypeDeclaration"></a>[118]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"as" <a href=
"#doc-xquery-SequenceType">SequenceType</a></code></td>
</tr>
</tbody>
</table>
<p>A <b>quantified expression</b> begins with a <b>quantifier</b>,
which is the keyword <code>some</code> or <code>every</code>,
followed by one or more in-clauses that are used to bind variables,
followed by the keyword <code>satisfies</code> and a test
expression. Each in-clause associates a variable with an expression
that returns a sequence of items, called the <b>binding
sequence</b> for that variable. The in-clauses generate tuples of
variable bindings, including a tuple for each combination of items
in the binding sequences of the respective variables. Conceptually,
the test expression is evaluated for each tuple of variable
bindings. Results depend on the <a title="effective boolean value"
href="#dt-ebv">effective boolean value</a> of the test expressions,
as defined in <a href="#id-ebv"><b>2.4.3 Effective Boolean
Value</b></a>. The value of the quantified expression is defined by
the following rules:</p>
<ol class="enumar">
<li>
<p>If the quantifier is <code>some</code>, the quantified
expression is <code>true</code> if at least one evaluation of the
test expression has the <a title="effective boolean value" href=
"#dt-ebv">effective boolean value</a> <code>true</code>; otherwise
the quantified expression is <code>false</code>. This rule implies
that, if the in-clauses generate zero binding tuples, the value of
the quantified expression is <code>false</code>.</p>
</li>
<li>
<p>If the quantifier is <code>every</code>, the quantified
expression is <code>true</code> if every evaluation of the test
expression has the <a title="effective boolean value" href=
"#dt-ebv">effective boolean value</a> <code>true</code>; otherwise
the quantified expression is <code>false</code>. This rule implies
that, if the in-clauses generate zero binding tuples, the value of
the quantified expression is <code>true</code>.</p>
</li>
</ol>
<p>The scope of a variable bound in a quantified expression
comprises all subexpressions of the quantified expression that
appear after the variable binding. The scope does not include the
expression to which the variable is bound.</p>
<div class="xquery">
<p class="xquery">Each variable bound in an in-clause of a
quantified expression may have an optional <a href=
"#doc-xquery-TypeDeclaration">type declaration</a>. If the type of
a value bound to the variable does not match the declared type
according to the rules for <a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>, a <a title=
"type error" href="#dt-type-error">type error</a> is raised
[<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].</p>
</div>
<p>The order in which test expressions are evaluated for the
various binding tuples is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>. If the
quantifier is <code>some</code>, an implementation may return
<code>true</code> as soon as it finds one binding tuple for which
the test expression has an <a title="effective boolean value" href=
"#dt-ebv">effective boolean value</a> of <code>true</code>, and it
may raise a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> as soon as it finds one
binding tuple for which the test expression raises an error.
Similarly, if the quantifier is <code>every</code>, an
implementation may return <code>false</code> as soon as it finds
one binding tuple for which the test expression has an <a title=
"effective boolean value" href="#dt-ebv">effective boolean
value</a> of <code>false</code>, and it may raise a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a> as soon
as it finds one binding tuple for which the test expression raises
an error. As a result of these rules, the value of a quantified
expression is not deterministic in the presence of errors, as
illustrated in the examples below.</p>
<p>Here are some examples of quantified expressions:</p>
<ul>
<li>
<p>This expression is <code>true</code> if every <code>part</code>
element has a <code>discounted</code> attribute (regardless of the
values of these attributes):</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
every $part in /parts/part satisfies $part/@discounted
</pre></div>
</div>
</li>
<li>
<p>This expression is <code>true</code> if at least one
<code>employee</code> element satisfies the given comparison
expression:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
some $emp in /emps/employee satisfies 
     ($emp/bonus &gt; 0.25 * $emp/salary)
</pre></div>
</div>
</li>
<li>
<p>In the following examples, each quantified expression evaluates
its test expression over nine tuples of variable bindings, formed
from the Cartesian product of the sequences <code>(1, 2, 3)</code>
and <code>(2, 3, 4)</code>. The expression beginning with
<code>some</code> evaluates to <code>true</code>, and the
expression beginning with <code>every</code> evaluates to
<code>false</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">some $x in (1, 2, 3), $y in (2, 3, 4) 
     satisfies $x + $y = 4</span></span>
</pre></div>
</div>
<div class="parse-test">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">every $x in (1, 2, 3), $y in (2, 3, 4) 
     satisfies $x + $y = 4</span></span>
</pre></div>
</div>
</li>
<li>
<p>This quantified expression may either return <code>true</code>
or raise a <a title="type error" href="#dt-type-error">type
error</a>, since its test expression returns <code>true</code> for
one variable binding and raises a <a title="type error" href=
"#dt-type-error">type error</a> for another:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
some $x in (1, 2, "cat") satisfies $x * 2 = 4
</pre></div>
</div>
</li>
<li>
<p>This quantified expression may either return <code>false</code>
or raise a <a title="type error" href="#dt-type-error">type
error</a>, since its test expression returns <code>false</code> for
one variable binding and raises a <a title="type error" href=
"#dt-type-error">type error</a> for another:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
every $x in (1, 2, "cat") satisfies $x * 2 = 4
</pre></div>
</div>
</li>
<li class="xquery">
<p>This quantified expression contains a <a href=
"#doc-xquery-TypeDeclaration">type declaration</a> that is not
satisfied by every item in the test expression. If the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is implemented, this expression raises a
<a title="type error" href="#dt-type-error">type error</a> during
the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>. Otherwise, the
expression may either return <code>true</code> or raise a <a title=
"type error" href="#dt-type-error">type error</a> during the
<a title="dynamic evaluation phase" href=
"#dt-dynamic-evaluation">dynamic evaluation phase</a>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div2">
<h3><a name="id-expressions-on-datatypes" id=
"id-expressions-on-datatypes"></a>3.12 Expressions on
SequenceTypes</h3>
<p><span class="xquery"><span class="xquery">In addition to their
use in function parameters and results,</span></span> <a title=
"sequence type" href="#dt-sequence-type">sequence types</a> are
used in <code>instance of</code>, <span class="xquery"><span class=
"xquery"><code>typeswitch</code>,</span></span> <code>cast</code>,
<code>castable</code>, and <code>treat</code> expressions.</p>
<div class="div3">
<h4><a name="id-instance-of" id="id-instance-of"></a>3.12.1
Instance Of</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-InstanceofExpr" id=
"doc-xquery-InstanceofExpr"></a>[54]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-InstanceofExpr">InstanceofExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-TreatExpr">TreatExpr</a> (
"instance" "of" <a href="#doc-xquery-SequenceType">SequenceType</a>
)?</code></td>
</tr>
</tbody>
</table>
<p>The boolean operator <code>instance of</code> returns
<code>true</code> if the value of its first operand matches the
<a href="#doc-xquery-SequenceType">SequenceType</a> in its second
operand, according to the rules for <a title=
"SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>; otherwise it
returns <code>false</code>. For example:</p>
<ul>
<li>
<p><code>5 instance of xs:integer</code></p>
<p>This example returns <code>true</code> because the given value
is an instance of the given type.</p>
</li>
<li>
<p><code>5 instance of xs:decimal</code></p>
<p>This example returns <code>true</code> because the given value
is an integer literal, and <code>xs:integer</code> is derived by
restriction from <code>xs:decimal</code>.</p>
</li>
<li class="xquery">
<p><code>&lt;a&gt;{5}&lt;/a&gt; instance of xs:integer</code></p>
<p>This example returns <code>false</code> because the given value
is an element rather than an integer.</p>
</li>
<li>
<p><code>(5, 6) instance of xs:integer+</code></p>
<p>This example returns <code>true</code> because the given
sequence contains two integers, and is a valid instance of the
specified type.</p>
</li>
<li>
<p><code>. instance of element()</code></p>
<p>This example returns <code>true</code> if the context item is an
element node or <code>false</code> if the context item is defined
but is not an element node. If the context item is <a title=
"undefined" href="#dt-undefined">undefined</a>, a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a> is
raised [<a href="#ERRXPDY0002" title=
"err:XPDY0002">err:XPDY0002</a>].</p>
</li>
</ul>
</div>
<div class="xquery">
<div class="div3">
<h4><a name="id-typeswitch" id="id-typeswitch"></a>3.12.2
Typeswitch</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-TypeswitchExpr" id=
"doc-xquery-TypeswitchExpr"></a>[43]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TypeswitchExpr" class=
"xquery">TypeswitchExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"typeswitch" "(" <a href="#doc-xquery-Expr">Expr</a> ")"
<a href="#doc-xquery-CaseClause">CaseClause</a>+ "default" ("$"
<a href="#doc-xquery-VarName">VarName</a>)? "return" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CaseClause" id=
"doc-xquery-CaseClause"></a>[44]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CaseClause" class=
"xquery">CaseClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"case" ("$" <a href="#doc-xquery-VarName">VarName</a>
"as")? <a href="#doc-xquery-SequenceType">SequenceType</a> "return"
<a href="#doc-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
</table>
<div class="xquery">
<p class="xquery">The <b>typeswitch</b> expression chooses one of
several expressions to evaluate based on the <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a> of an input
value.</p>
</div>
<div class="xquery">
<p class="xquery">In a <code>typeswitch</code> expression, the
<code>typeswitch</code> keyword is followed by an expression
enclosed in parentheses, called the <b>operand expression</b>. This
is the expression whose type is being tested. The remainder of the
<code>typeswitch</code> expression consists of one or more
<code>case</code> clauses and a <code>default</code> clause.</p>
</div>
<div class="xquery">
<p class="xquery">Each <code>case</code> clause specifies a
<a href="#doc-xquery-SequenceType">SequenceType</a> followed by a
<code>return</code> expression. [<a name="dt-effective-case" id=
"dt-effective-case" title="effective case">Definition</a>: The
<b>effective case</b> in a <code>typeswitch</code> expression is
the first <code>case</code> clause such that the value of the
operand expression matches the <a href=
"#doc-xquery-SequenceType">SequenceType</a> in the
<code>case</code> clause, using the rules of <a title=
"SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>.] The value
of the <code>typeswitch</code> expression is the value of the
<code>return</code> expression in the effective case. If the value
of the operand expression does not match any <a href=
"#doc-xquery-SequenceType">SequenceType</a> named in a
<code>case</code> clause, the value of the <code>typeswitch</code>
expression is the value of the <code>return</code> expression in
the <code>default</code> clause.</p>
</div>
<p>In a <code>case</code> or <code>default</code> clause, if the
value to be returned depends on the value of the operand
expression, the clause must specify a variable name. Within the
<code>return</code> expression of the <code>case</code> or
<code>default</code> clause, this variable name is bound to the
value of the operand expression. Inside a <code>case</code> clause,
the <a title="static type" href="#dt-static-type">static type</a>
of the variable is the <a href=
"#doc-xquery-SequenceType">SequenceType</a> named in the
<code>case</code> clause. Inside a <code>default</code> clause, the
static type of the variable is the same as the static type of the
operand expression. If the value to be returned by a
<code>case</code> or <code>default</code> clause does not depend on
the value of the operand expression, the clause need not specify a
variable.</p>
<p>The scope of a variable binding in a <code>case</code> or
<code>default</code> clause comprises that clause. It is not an
error for more than one <code>case</code> or <code>default</code>
clause in the same <code>typeswitch</code> expression to bind
variables with the same name.</p>
<p>A special rule applies to propagation of <a title=
"dynamic error" href="#dt-dynamic-error">dynamic errors</a> by
<code>typeswitch</code> expressions. A <code>typeswitch</code>
expression ignores (does not raise) any dynamic errors encountered
in <code>case</code> clauses other than the <a title=
"effective case" href="#dt-effective-case">effective case</a>.
Dynamic errors encountered in the <code>default</code> clause are
raised only if there is no <a title="effective case" href=
"#dt-effective-case">effective case</a>.</p>
<div class="xquery">
<p class="xquery">The following example shows how a
<code>typeswitch</code> expression might be used to process an
expression in a way that depends on its <a title="dynamic type"
href="#dt-dynamic-type">dynamic type</a>.</p>
</div>
<div class="xquery">
<div class="exampleInner">
<pre>
<span class="parse-test"><span class=
"parse-test">typeswitch($customer/billing-address)
   case $a as element(*, USAddress) return $a/state
   case $a as element(*, CanadaAddress) return $a/province
   case $a as element(*, JapanAddress) return $a/prefecture
   default return "unknown"</span></span>
</pre></div>
</div>
</div>
</div>
<div class="div3">
<h4><a name="id-cast" id="id-cast"></a>3.12.3 Cast</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CastExpr" id=
"doc-xquery-CastExpr"></a>[57]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CastExpr">CastExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-UnaryExpr">UnaryExpr</a> ( "cast"
"as" <a href="#doc-xquery-SingleType">SingleType</a> )?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-SingleType" id=
"doc-xquery-SingleType"></a>[117]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-SingleType">SingleType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AtomicType">AtomicType</a>
"?"?</code></td>
</tr>
</tbody>
</table>
<p>Occasionally it is necessary to convert a value to a specific
datatype. For this purpose, XQuery provides a <code>cast</code>
expression that creates a new value of a specific type based on an
existing value. A <code>cast</code> expression takes two operands:
an <b>input expression</b> and a <b>target type</b>. The type of
the input expression is called the <b>input type</b>. The target
type must be an atomic type that is in the <a title=
"in-scope schema type" href="#dt-is-types">in-scope schema
types</a> [<a href="#ERRXPST0051" title=
"err:XPST0051">err:XPST0051</a>]. In addition, the target type
cannot be <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code>
[<a href="#ERRXPST0080" title="err:XPST0080">err:XPST0080</a>]. The
optional occurrence indicator "<code>?</code>" denotes that an
empty sequence is permitted. If the target type has no namespace
prefix, it is considered to be in the <a title=
"default element/type namespace" href="#dt-def-elemtype-ns">default
element/type namespace</a>. The semantics of the <code>cast</code>
expression are as follows:</p>
<ol class="enumar">
<li>
<p><a title="atomization" href="#dt-atomization">Atomization</a> is
performed on the input expression.</p>
</li>
<li>
<p>If the result of atomization is a sequence of more than one
atomic value, a <a title="type error" href="#dt-type-error">type
error</a> is raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
<li>
<p>If the result of atomization is an empty sequence:</p>
<ol class="enumla">
<li>
<p>If <code>?</code> is specified after the target type, the result
of the <code>cast</code> expression is an empty sequence.</p>
</li>
<li>
<p>If <code>?</code> is not specified after the target type, a
<a title="type error" href="#dt-type-error">type error</a> is
raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
</li>
</ol>
</li>
<li>
<p>If the result of atomization is a single atomic value, the
result of the cast expression depends on the input type and the
target type. In general, the cast expression attempts to create a
new value of the target type based on the input value. Only certain
combinations of input type and target type are supported. A summary
of the rules are listed below— the normative definition of these
rules is given in <a href="#FunctionsAndOperators">[XQuery 1.0 and
XPath 2.0 Functions and Operators (Second Edition)]</a>. For the
purpose of these rules, an implementation may determine that one
type is derived by restriction from another type either by
examining the <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a> or by using an
alternative, <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>
mechanism such as a data dictionary.</p>
<ol class="enumla">
<li>
<p><code>cast</code> is supported for the combinations of input
type and target type listed in <a href=
"http://www.w3.org/TR/xpath-functions/#casting-from-primitive-to-primitive">
Section 17.1 Casting from primitive types to primitive
types</a><sup><small>FO</small></sup>. For each of these
combinations, both the input type and the target type are primitive
<a title="schema type" href="#dt-schema-type">schema types</a>. For
example, a value of type <code>xs:string</code> can be cast into
the schema type <code>xs:decimal</code>. For each of these built-in
combinations, the semantics of casting are specified in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
<p>If the target type of a <code>cast</code> expression is
<code>xs:QName</code>, or is a type that is derived from
<code>xs:QName</code> or <code>xs:NOTATION</code>, and if the base
type of the input is not the same as the base type of the target
type, then the input expression must be a string literal [<a href=
"#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The reason for this rule is that construction of an instance of
one of these target types from a string requires knowledge about
namespace bindings. If the input expression is a non-literal
string, it might be derived from an input document whose namespace
bindings are different from the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>.</p>
</div>
</li>
<li>
<p><code>cast</code> is supported if the input type is a
non-primitive atomic type that is derived by restriction from the
target type. In this case, the input value is mapped into the value
space of the target type, unchanged except for its type. For
example, if <code>shoesize</code> is derived by restriction from
<code>xs:integer</code>, a value of type <code>shoesize</code> can
be cast into the schema type <code>xs:integer</code>.</p>
</li>
<li>
<p><code>cast</code> is supported if the target type is a
non-primitive atomic type and the input type is
<code>xs:string</code> or <code>xs:untypedAtomic</code>. The input
value is first converted to a value in the lexical space of the
target type by applying the whitespace normalization rules for the
target type (as defined in <a href="#XMLSchema">[XML Schema]</a>).
The lexical value is then converted to the value space of the
target type using the schema-defined rules for the target type. If
the input value fails to satisfy some facet of the target type, a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
may be raised as specified in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
</li>
<li>
<p><code>cast</code> is supported if the target type is a
non-primitive atomic type that is derived by restriction from the
input type. The input value must satisfy all the facets of the
target type (in the case of the pattern facet, this is checked by
generating a string representation of the input value, using the
rules for casting to <code>xs:string</code>). The resulting value
is the same as the input value, but with a different <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a>.</p>
</li>
<li>
<p>If a primitive type P1 can be cast into a primitive type P2,
then any type derived by restriction from P1 can be cast into any
type derived by restriction from P2, provided that the facets of
the target type are satisfied. First the input value is cast to P1
using rule (b) above. Next, the value of type P1 is cast to the
type P2, using rule (a) above. Finally, the value of type P2 is
cast to the target type, using rule (d) above.</p>
</li>
<li>
<p>For any combination of input type and target type that is not in
the above list, a <code>cast</code> expression raises a <a title=
"type error" href="#dt-type-error">type error</a> [<a href=
"#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>].</p>
</li>
</ol>
</li>
</ol>
<p>If casting from the input type to the target type is supported
but nevertheless it is not possible to cast the input value into
the value space of the target type, a <a title="dynamic error"
href="#dt-dynamic-error">dynamic error</a> is raised.
[err:FORG0001] This includes the case when any facet of the target
type is not satisfied. For example, the expression
<code>"2003-02-31" cast as xs:date</code> would raise a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a>.</p>
</div>
<div class="div3">
<h4><a name="id-castable" id="id-castable"></a>3.12.4 Castable</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CastableExpr" id=
"doc-xquery-CastableExpr"></a>[56]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-CastableExpr">CastableExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-CastExpr">CastExpr</a> ( "castable"
"as" <a href="#doc-xquery-SingleType">SingleType</a> )?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e15164.doc-xquery-SingleType" id=
"noid_d2e15164.doc-xquery-SingleType"></a>[117]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-SingleType">SingleType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AtomicType">AtomicType</a>
"?"?</code></td>
</tr>
</tbody>
</table>
<p>XQuery provides an expression that tests whether a given value
is castable into a given target type. The target type must be an
atomic type that is in the <a title="in-scope schema type" href=
"#dt-is-types">in-scope schema types</a> [<a href="#ERRXPST0051"
title="err:XPST0051">err:XPST0051</a>]. In addition, the target
type cannot be <code>xs:NOTATION</code> or
<code>xs:anyAtomicType</code> [<a href="#ERRXPST0080" title=
"err:XPST0080">err:XPST0080</a>]. The optional occurrence indicator
"<code>?</code>" denotes that an empty sequence is permitted.</p>
<p>The expression <code>E castable as T</code> returns
<code>true</code> if the result of evaluating <code>E</code> can be
successfully cast into the target type <code>T</code> by using a
<code>cast</code> expression; otherwise it returns
<code>false</code>. If evaluation of <code>E</code> fails with a
dynamic error, the <code>castable</code> expression as a whole
fails. The <code>castable</code> expression can be used as a
<a title="predicate" href="#dt-predicate">predicate</a> to avoid
errors at evaluation time. It can also be used to select an
appropriate type for processing of a given value, as illustrated in
the following example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
if ($x castable as hatsize) 
   then $x cast as hatsize 
   else if ($x castable as IQ) 
   then $x cast as IQ 
   else $x cast as xs:string
</pre></div>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>If the target type of a <code>castable</code> expression is
<code>xs:QName</code>, or is a type that is derived from
<code>xs:QName</code> or <code>xs:NOTATION</code>, and the input
argument of the expression is of type <code>xs:string</code> but it
is not a literal string, the result of the <code>castable</code>
expression is <code>false</code>.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-constructor-functions" id=
"id-constructor-functions"></a>3.12.5 Constructor Functions</h4>
<p>For every atomic type in the <a title="in-scope schema type"
href="#dt-is-types">in-scope schema types</a> (except
<code>xs:NOTATION</code> and <code>xs:anyAtomicType</code>, which
are not instantiable), a <b>constructor function</b> is implicitly
defined. In each case, the name of the constructor function is the
same as the name of its target type (including namespace). The
signature of the constructor function for type <em>T</em> is as
follows:</p>
<div class="exampleInner">
<pre>
<em>T</em>($arg as xs:anyAtomicType?) as <em>T?</em>
</pre></div>
<p>[<a name="dt-constructor-function" id="dt-constructor-function"
title="constructor function">Definition</a>: The <b>constructor
function</b> for a given type is used to convert instances of other
atomic types into the given type. The semantics of the constructor
function call <code>T($arg)</code> are defined to be equivalent to
the expression <code>(($arg) cast as T?)</code>.]</p>
<p>The constructor functions for <code>xs:QName</code> and for
types derived from <code>xs:QName</code> and
<code>xs:NOTATION</code> require their arguments to be string
literals or to have a base type that is the same as the base type
of the target type; otherwise a type error [<a href="#ERRXPTY0004"
title="err:XPTY0004">err:XPTY0004</a>] is raised. This rule is
consistent with the semantics of <code>cast</code> expressions for
these types, as defined in <a href="#id-cast"><b>3.12.3
Cast</b></a>.</p>
<p>The following examples illustrate the use of constructor
functions:</p>
<ul>
<li>
<p>This example is equivalent to <code>("2000-01-01" cast as
xs:date?)</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
xs:date("2000-01-01")
</pre></div>
</div>
</li>
<li>
<p>This example is equivalent to <code>(($floatvalue * 0.2E-5) cast
as xs:decimal?)</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
xs:decimal($floatvalue * 0.2E-5)
</pre></div>
</div>
</li>
<li>
<p>This example returns a <code>xs:dayTimeDuration</code> value
equal to 21 days. It is equivalent to <code>("P21D" cast as
xs:dayTimeDuration?)</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
xs:dayTimeDuration("P21D")
</pre></div>
</div>
</li>
<li>
<p>If <code>usa:zipcode</code> is a user-defined atomic type in the
<a title="in-scope schema type" href="#dt-is-types">in-scope schema
types</a>, then the following expression is equivalent to the
expression <code>("12345" cast as usa:zipcode?)</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
usa:zipcode("12345")
</pre></div>
</div>
</li>
</ul>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>An instance of an atomic type that is not in a namespace can be
constructed in either of the following ways:</p>
<ul>
<li>
<p>By using a <code>cast</code> expression, if the <a title=
"default element/type namespace" href="#dt-def-elemtype-ns">default
element/type namespace</a> is "none". <span class=
"xquery"><span class="xquery">(See <a href=
"#id-default-namespace"><b>4.13 Default Namespace
Declaration</b></a> for how to undeclare the <a title=
"default element/type namespace" href="#dt-def-elemtype-ns">default
element/type namespace</a>).</span></span></p>
<div class="parse-test">
<div class="exampleInner">
<pre>
17 cast as apple
</pre></div>
</div>
</li>
<li>
<p>By using a constructor function, if the <a title=
"default function namespace" href="#dt-def-fn-ns">default function
namespace</a> is "none". <span class="xquery"><span class=
"xquery">(See <a href="#id-default-namespace"><b>4.13 Default
Namespace Declaration</b></a> for how to undeclare the <a title=
"default function namespace" href="#dt-def-fn-ns">default function
namespace</a>).</span></span></p>
<div class="parse-test">
<div class="exampleInner">
<pre>
apple(17)
</pre></div>
</div>
</li>
</ul>
</div>
</div>
<div class="div3">
<h4><a name="id-treat" id="id-treat"></a>3.12.6 Treat</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-TreatExpr" id=
"doc-xquery-TreatExpr"></a>[55]&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-TreatExpr">TreatExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-CastableExpr">CastableExpr</a> (
"treat" "as" <a href="#doc-xquery-SequenceType">SequenceType</a>
)?</code></td>
</tr>
</tbody>
</table>
<p>XQuery provides an expression called <code>treat</code> that can
be used to modify the <a title="static type" href=
"#dt-static-type">static type</a> of its operand.</p>
<p>Like <code>cast</code>, the <code>treat</code> expression takes
two operands: an expression and a <a href=
"#doc-xquery-SequenceType">SequenceType</a>. Unlike
<code>cast</code>, however, <code>treat</code> does not change the
<a title="dynamic type" href="#dt-dynamic-type">dynamic type</a> or
value of its operand. Instead, the purpose of <code>treat</code> is
to ensure that an expression has an expected dynamic type at
evaluation time.</p>
<p>The semantics of <em><code>expr1</code></em> <code>treat
as</code> <em><code>type1</code></em> are as follows:</p>
<ul>
<li>
<p>During static analysis:</p>
<p>The <a title="static type" href="#dt-static-type">static
type</a> of the <code>treat</code> expression is
<em><code>type1</code></em>. This enables the expression to be used
as an argument of a function that requires a parameter of
<em><code>type1</code></em>.</p>
</li>
<li>
<p>During expression evaluation:</p>
<p>If <em><code>expr1</code></em> matches
<em><code>type1</code></em>, using the rules for <a title=
"SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>, the
<code>treat</code> expression returns the value of
<em><code>expr1</code></em>; otherwise, it raises a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a>
[<a href="#ERRXPDY0050" title="err:XPDY0050">err:XPDY0050</a>]. If
the value of <em><code>expr1</code></em> is returned, its identity
is preserved. The <code>treat</code> expression ensures that the
value of its expression operand conforms to the expected type at
run-time.</p>
</li>
<li>
<p>Example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
$myaddress treat as element(*, USAddress)
</pre></div>
</div>
<p>The <a title="static type" href="#dt-static-type">static
type</a> of <code>$myaddress</code> may be <code>element(*,
Address)</code>, a less specific type than <code>element(*,
USAddress)</code>. However, at run-time, the value of
<code>$myaddress</code> must match the type <code>element(*,
USAddress)</code> using rules for <a title="SequenceType matching"
href="#dt-sequencetype-matching">SequenceType matching</a>;
otherwise a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXPDY0050" title="err:XPDY0050">err:XPDY0050</a>].</p>
</li>
</ul>
</div>
</div>
<div class="xquery">
<div class="div2">
<h3><a name="id-validate" id="id-validate"></a>3.13 Validate
Expressions</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ValidateExpr" id=
"doc-xquery-ValidateExpr"></a>[63]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ValidateExpr" class=
"xquery">ValidateExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"validate" <a href=
"#doc-xquery-ValidationMode">ValidationMode</a>? "{" <a href=
"#doc-xquery-Expr">Expr</a> "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ValidationMode" id=
"doc-xquery-ValidationMode"></a>[64]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ValidationMode" class=
"xquery">ValidationMode</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"lax" | "strict"</code></td>
</tr>
</tbody>
</table>
<p>A <code>validate</code> expression can be used to validate a
document node or an element node with respect to the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a>, using the schema validation process defined in
<a href="#XMLSchema">[XML Schema]</a>. If the operand of a
<code>validate</code> expression does not evaluate to exactly one
document or element node, a <a title="type error" href=
"#dt-type-error">type error</a> is raised [<a href="#ERRXQTY0030"
title="err:XQTY0030">err:XQTY0030</a>]. In this specification, the
node that is the operand of a <code>validate</code> expression is
called the <b>operand node</b>.</p>
<p>A <code>validate</code> expression returns a new node with its
own identity and with no parent. The new node and its descendants
are given <a title="type annotation" href=
"#dt-type-annotation">type annotations</a> that are generated by
applying a validation process to the operand node. In some cases,
default values may also be generated by the validation process.</p>
<p>A <code>validate</code> expression may optionally specify a
<a href="#doc-xquery-ValidationMode">validation mode</a>. The
default <a href="#doc-xquery-ValidationMode">validation mode</a> is
<code>strict</code>. The result of a <code>validate</code>
expression is defined by the following rules.</p>
<ol class="enumar">
<li>
<p>If the operand node is a document node, its children must
consist of exactly one element node and zero or more comment and
processing instruction nodes, in any order; otherwise, a <a title=
"dynamic error" href="#dt-dynamic-error">dynamic error</a>
[<a href="#ERRXQDY0061" title="err:XQDY0061">err:XQDY0061</a>] is
raised.</p>
</li>
<li>
<p>The operand node is converted to an XML Information Set
(<a href="#XINFO">[XML Infoset]</a>) according to the "Infoset
Mapping" rules defined in <a href="#datamodel">[XQuery 1.0 and
XPath 2.0 Data Model (Second Edition)]</a>. Note that this process
discards any existing <a title="type annotation" href=
"#dt-type-annotation">type annotations</a>.</p>
</li>
<li>
<p>Validity assessment is carried out on the root element
information item of the resulting Infoset, using the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a> as the effective schema. The process of validation
applies recursively to contained elements and attributes to the
extent required by the effective schema. During validity
assessment, the following special rules are in effect:</p>
<ol class="enumla">
<li>
<p>If <a href="#doc-xquery-ValidationMode">validation mode</a> is
<code>strict</code>, then there must be a top-level element
declaration in the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a> that matches the
root element information item in the Infoset, and schema-validity
assessment is carried out using that declaration in accordance with
item 2 of <a href="#XMLSchema">[XML Schema]</a> Part 1, section
5.2, "Assessing Schema-Validity." If there is no such element
declaration, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXQDY0084" title="err:XQDY0084">err:XQDY0084</a>].</p>
</li>
<li>
<p>If <a href="#doc-xquery-ValidationMode">validation mode</a> is
<code>lax</code>, then schema-validity assessment is carried out in
accordance with item 3 of <a href="#XMLSchema">[XML Schema]</a>
Part 1, section 5.2, "Assessing Schema-Validity."</p>
<p>If <a href="#doc-xquery-ValidationMode">validation mode</a> is
<code>lax</code> and the root element information item has neither
a top-level element declaration nor an <code>xsi:type</code>
attribute, <a href="#XMLSchema">[XML Schema]</a> defines the
recursive checking of children and attributes as optional. During
processing of an XQuery <code>validate</code> expression, this
recursive checking is required.</p>
</li>
<li>
<p>If the operand node is an element node, the validation rules
named "Validation Root Valid (ID/IDREF)" is not applied. This means
that document-level constraints relating to uniqueness and
referential integrity are not enforced.</p>
</li>
<li>
<p>There is no check that the document contains unparsed entities
whose names match the values of nodes of type
<code>xs:ENTITY</code> or <code>xs:ENTITIES</code>.</p>
</li>
<li>
<p>There is no check that the document contains notations whose
names match the values of nodes of type
<code>xs:NOTATION</code>.</p>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Validity assessment is affected by the presence or absence of
<code>xsi:type</code> attributes on the elements being validated,
and may generate new information items such as default
attributes.</p>
</div>
</li>
<li>
<p>The next step depends on <a href=
"#doc-xquery-ValidationMode">validation mode</a> and on the
<code>validity</code> property of the root element information item
in the PSVI that results from the validation process.</p>
<ol class="enumla">
<li>
<p>If the <code>validity</code> property of the root element
information item is <code>valid</code> (for any <a href=
"#doc-xquery-ValidationMode">validation mode</a>), or if <a href=
"#doc-xquery-ValidationMode">validation mode</a> is
<code>lax</code> and the <code>validity</code> property of the root
element information item is <code>notKnown</code>, the PSVI is
converted back into an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a> as described in <a href=
"#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a> Section 3.3, "Construction from a PSVI". The
resulting node (a new node of the same kind as the operand node) is
returned as the result of the <code>validate</code> expression.</p>
</li>
<li>
<p>Otherwise, a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> is raised [<a href=
"#ERRXQDY0027" title="err:XQDY0027">err:XQDY0027</a>].</p>
</li>
</ol>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The effect of these rules is as follows: If <a href=
"#doc-xquery-ValidationMode">validation mode</a> is
<code>strict</code>, the validated element must have a top-level
element declaration in the effective schema, and must conform to
this declaration. If <a href=
"#doc-xquery-ValidationMode">validation mode</a> is
<code>lax</code>, the validated element must conform to its
top-level element declaration if such a declaration exists in the
effective schema. If <a href=
"#doc-xquery-ValidationMode">validation mode</a> is
<code>lax</code> and there is no top-level element declaration for
the element, and the element has an <code>xsi:type</code>
attribute, then the <code>xsi:type</code> attribute must name a
top-level type definition in the effective schema, and the element
must conform to that type. The validated element corresponds either
to the operand node or (if the operand node is a document node) to
its element child.</p>
</div>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>During conversion of the PSVI into an <a title="XDM instance"
href="#dt-data-model-instance">XDM instance</a> after validation,
any element information items whose validity property is
<code>notKnown</code> are converted into element nodes with
<a title="type annotation" href="#dt-type-annotation">type
annotation</a> <code>xs:anyType</code>, and any attribute
information items whose validity property is <code>notKnown</code>
are converted into attribute nodes with <a title="type annotation"
href="#dt-type-annotation">type annotation</a>
<code>xs:untypedAtomic</code>, as described in <a href=
"http://www.w3.org/TR/xpath-datamodel/#PSVI2NodeTypes">Section
3.3.1.1 Element and Attribute Node Type
Names</a><sup><small>DM</small></sup>.</p>
</div>
</div>
</div>
<div class="xquery">
<div class="div2">
<h3><a name="id-extension-expressions" id=
"id-extension-expressions"></a>3.14 Extension Expressions</h3>
<p>[<a name="dt-extension-expression" id="dt-extension-expression"
title="extension expression">Definition</a>: An <b>extension
expression</b> is an expression whose semantics are <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.] Typically
a particular extension will be recognized by some implementations
and not by others. The syntax is designed so that extension
expressions can be successfully parsed by all implementations, and
so that fallback behavior can be defined for implementations that
do not recognize a particular extension.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ExtensionExpr" id=
"doc-xquery-ExtensionExpr"></a>[65]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ExtensionExpr" class=
"xquery">ExtensionExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Pragma">Pragma</a>+ "{" <a href=
"#doc-xquery-Expr">Expr</a>? "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Pragma" id=
"doc-xquery-Pragma"></a>[66]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Pragma" class=
"xquery">Pragma</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"(#" <a href="#prod-xquery-S">S</a>? <a href=
"#prod-xquery-QName">QName</a> (<a href="#prod-xquery-S">S</a>
<a href="#doc-xquery-PragmaContents">PragmaContents</a>)?
"#)"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PragmaContents" id=
"doc-xquery-PragmaContents"></a>[67]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-PragmaContents" class=
"xquery">PragmaContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>* - (Char* '#)'
Char*))</code></td>
</tr>
</tbody>
</table>
<p>An extension expression consists of one or more <b>pragmas</b>,
followed by an expression enclosed in curly braces. [<a name=
"dt-pragma" id="dt-pragma" title="pragma">Definition</a>: A
<b>pragma</b> is denoted by the delimiters <code>(#</code> and
<code>#)</code>, and consists of an identifying QName followed by
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> content.]
The content of a pragma may consist of any string of characters
that does not contain the ending delimiter <code>#)</code>. The
QName of a pragma must resolve to a namespace URI and local name,
using the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> [<a href=
"#ERRXPST0081" title="err:XPST0081">err:XPST0081</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Since there is no default namespace for pragmas, a pragma QName
must include a namespace prefix.</p>
</div>
<p>Each implementation recognizes an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> set of
namespace URIs used to denote pragmas.</p>
<p>If the namespace part of a pragma QName is not recognized by the
implementation as a pragma namespace, then the pragma is ignored.
If all the pragmas in an <a href=
"#doc-xquery-ExtensionExpr">ExtensionExpr</a> are ignored, then the
value of the <a href="#doc-xquery-ExtensionExpr">ExtensionExpr</a>
is the value of the expression enclosed in curly braces; if this
expression is absent, then a <a title="static error" href=
"#dt-static-error">static error</a> is raised [<a href=
"#ERRXQST0079" title="err:XQST0079">err:XQST0079</a>].</p>
<p>If an implementation recognizes the namespace of one or more
pragmas in an <a href=
"#doc-xquery-ExtensionExpr">ExtensionExpr</a>, then the value of
the <a href="#doc-xquery-ExtensionExpr">ExtensionExpr</a>,
including its error behavior, is <a title="implementation defined"
href="#dt-implementation-defined">implementation-defined</a>. For
example, an implementation that recognizes the namespace of a
pragma QName, but does not recognize the local part of the QName,
might choose either to raise an error or to ignore the pragma.</p>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0013" title=
"err:XQST0013">err:XQST0013</a>] if an implementation recognizes a
pragma but determines that its content is invalid.</p>
<p>If an implementation recognizes a pragma, it must report any
static errors in the following expression even if it will not
evaluate that expression (however, static type errors are raised
only if the <a title="static typing feature" href=
"#dt-static-typing-feature">Static Typing Feature</a> is in
effect.)</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The following examples illustrate three ways in which extension
expressions might be used.</p>
<ul>
<li>
<p>A pragma can be used to furnish a hint for how to evaluate the
following expression, without actually changing the result. For
example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare namespace exq = "http://example.org/XQueryImplementation";
   (# exq:use-index #)
      { $bib/book/author[name='Berners-Lee'] }
</pre></div>
</div>
<p>An implementation that recognizes the <code>exq:use-index</code>
pragma might use an index to evaluate the expression that follows.
An implementation that does not recognize this pragma would
evaluate the expression in its normal way.</p>
</li>
<li>
<p>A pragma might be used to modify the semantics of the following
expression in ways that would not (in the absence of the pragma) be
conformant with this specification. For example, a pragma might be
used to permit comparison of <code>xs:duration</code> values using
implementation-defined semantics (this would normally be an error).
Such changes to the language semantics must be scoped to the
expression contained within the curly braces following the
pragma.</p>
</li>
<li>
<p>A pragma might contain syntactic constructs that are evaluated
in place of the following expression. In this case, the following
expression itself (if it is present) provides a fallback for use by
implementations that do not recognize the pragma. For example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare namespace exq = "http://example.org/XQueryImplementation";
   for $x in
      (# exq:distinct //city by @country #)
      { //city[not(@country = preceding::city/@country)] }
   return f:show-city($x)
</pre></div>
</div>
<p>Here an implementation that recognizes the pragma will return
the result of evaluating the proprietary syntax <code>exq:distinct
//city by @country</code>, while an implementation that does not
recognize the pragma will instead return the result of the
expression <code>//city[not(@country =
preceding::city/@country)]</code>. If no fallback expression is
required, or if none is feasible, then the expression between the
curly braces may be omitted, in which case implementations that do
not recognize the pragma will raise a <a title="static error" href=
"#dt-static-error">static error</a>.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="xquery">
<div class="div1">
<div class="xquery">
<h2><a name="id-query-prolog" id="id-query-prolog"></a>4 Modules
and Prologs</h2>
</div>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Module" id=
"doc-xquery-Module"></a>[1]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Module" class=
"xquery">Module</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-VersionDecl">VersionDecl</a>?
(<a href="#doc-xquery-LibraryModule">LibraryModule</a> | <a href=
"#doc-xquery-MainModule">MainModule</a>)</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-MainModule" id=
"doc-xquery-MainModule"></a>[3]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-MainModule" class=
"xquery">MainModule</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Prolog">Prolog</a> <a href=
"#doc-xquery-QueryBody">QueryBody</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-LibraryModule" id=
"doc-xquery-LibraryModule"></a>[4]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-LibraryModule" class=
"xquery">LibraryModule</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ModuleDecl">ModuleDecl</a> <a href=
"#doc-xquery-Prolog">Prolog</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Prolog" id=
"doc-xquery-Prolog"></a>[6]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Prolog" class=
"xquery">Prolog</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>((<a href=
"#doc-xquery-DefaultNamespaceDecl">DefaultNamespaceDecl</a> |
<a href="#doc-xquery-Setter">Setter</a> | <a href=
"#doc-xquery-NamespaceDecl">NamespaceDecl</a> | <a href=
"#doc-xquery-Import">Import</a>) <a href=
"#doc-xquery-Separator">Separator</a>)* ((<a href=
"#doc-xquery-VarDecl">VarDecl</a> | <a href=
"#doc-xquery-FunctionDecl">FunctionDecl</a> | <a href=
"#doc-xquery-OptionDecl">OptionDecl</a>) <a href=
"#doc-xquery-Separator">Separator</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Setter" id=
"doc-xquery-Setter"></a>[7]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Setter" class=
"xquery">Setter</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-BoundarySpaceDecl">BoundarySpaceDecl</a> | <a href=
"#doc-xquery-DefaultCollationDecl">DefaultCollationDecl</a> |
<a href="#doc-xquery-BaseURIDecl">BaseURIDecl</a> | <a href=
"#doc-xquery-ConstructionDecl">ConstructionDecl</a> | <a href=
"#doc-xquery-OrderingModeDecl">OrderingModeDecl</a> | <a href=
"#doc-xquery-EmptyOrderDecl">EmptyOrderDecl</a> | <a href=
"#doc-xquery-CopyNamespacesDecl">CopyNamespacesDecl</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Import" id=
"doc-xquery-Import"></a>[8]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Import" class=
"xquery">Import</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-SchemaImport">SchemaImport</a> |
<a href="#doc-xquery-ModuleImport">ModuleImport</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Separator" id=
"doc-xquery-Separator"></a>[9]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Separator" class=
"xquery">Separator</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>";"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-QueryBody" id=
"doc-xquery-QueryBody"></a>[30]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QueryBody" class=
"xquery">QueryBody</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Expr">Expr</a></code></td>
</tr>
</tbody>
</table>
<p>A query can be assembled from one or more fragments called
<b>modules</b>. [<a name="dt-module" id="dt-module" title=
"module">Definition</a>: A <b>module</b> is a fragment of XQuery
code that conforms to the <a href="#doc-xquery-Module">Module</a>
grammar and can independently undergo the <a title=
"static analysis phase" href="#dt-static-analysis">static analysis
phase</a> described in <a href="#id-expression-processing"><b>2.2.3
Expression Processing</b></a>. Each module is either a <a title=
"main module" href="#dt-main-module">main module</a> or a <a title=
"library module" href="#dt-library-module">library module</a>.]</p>
<p>[<a name="dt-main-module" id="dt-main-module" title=
"main module">Definition</a>: A <b>main module</b> consists of a
<a title="Prolog" href="#dt-prolog">Prolog</a> followed by a
<a title="query body" href="#dt-queryBody">Query Body</a>.] A query
has exactly one main module. In a main module, the <a title=
"query body" href="#dt-queryBody">Query Body</a> can be evaluated,
and its value is the result of the query.</p>
<p>[<a name="dt-library-module" id="dt-library-module" title=
"library module">Definition</a>: A module that does not contain a
<a title="query body" href="#dt-queryBody">Query Body</a> is called
a <b>library module</b>. A library module consists of a <a title=
"module declaration" href="#dt-module-declaration">module
declaration</a> followed by a <a title="Prolog" href=
"#dt-prolog">Prolog</a>.] A library module cannot be evaluated
directly; instead, it provides function and variable declarations
that can be imported into other modules.</p>
<p>The XQuery syntax does not allow a <a title="module" href=
"#dt-module">module</a> to contain both a <a title=
"module declaration" href="#dt-module-declaration">module
declaration</a> and a <a title="query body" href=
"#dt-queryBody">Query Body</a>.</p>
<p>[<a name="dt-prolog" id="dt-prolog" title=
"Prolog">Definition</a>: A <b>Prolog</b> is a series of
declarations and imports that define the processing environment for
the <a title="module" href="#dt-module">module</a> that contains
the Prolog.] Each declaration or import is followed by a semicolon.
A Prolog is organized into two parts.</p>
<p>The first part of the Prolog consists of setters, imports,
namespace declarations, and default namespace declarations.
[<a name="dt-setter" id="dt-setter" title="setter">Definition</a>:
<b>Setters</b> are declarations that set the value of some property
that affects query processing, such as construction mode, ordering
mode, or default collation.] Namespace declarations and default
namespace declarations affect the interpretation of QNames within
the query. Imports are used to import definitions from schemas and
modules. [<a name="dt-target-namespace" id="dt-target-namespace"
title="target namespace">Definition</a>: Each imported schema or
module is identified by its <b>target namespace</b>, which is the
namespace of the objects (such as elements or functions) that are
defined by the schema or module.]</p>
<p>The second part of the Prolog consists of declarations of
variables, functions, and options. These declarations appear at the
end of the Prolog because they may be affected by declarations and
imports in the first part of the Prolog.</p>
<p>[<a name="dt-queryBody" id="dt-queryBody" title=
"query body">Definition</a>: The <b>Query Body</b>, if present,
consists of an expression that defines the result of the query.]
Evaluation of expressions is described in <a href=
"#id-expressions"><b>3 Expressions</b></a>. A module can be
evaluated only if it has a Query Body.</p>
<div class="div2">
<h3><a name="id-version-declaration" id=
"id-version-declaration"></a>4.1 Version Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-VersionDecl" id=
"doc-xquery-VersionDecl"></a>[2]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-VersionDecl" class=
"xquery">VersionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"xquery" "version" <a href=
"#doc-xquery-StringLiteral">StringLiteral</a> ("encoding" <a href=
"#doc-xquery-StringLiteral">StringLiteral</a>)? <a href=
"#doc-xquery-Separator">Separator</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-version-declaration" id="dt-version-declaration"
title="version declaration">Definition</a>: Any <a title="module"
href="#dt-module">module</a> may contain a <b>version
declaration</b>. If present, the version declaration occurs at the
beginning of the <a title="module" href="#dt-module">module</a> and
identifies the applicable XQuery syntax and semantics for the
<a title="module" href="#dt-module">module</a>.] The version number
"1.0" indicates a requirement that the <a title="module" href=
"#dt-module">module</a> must be processed by an implementation that
supports XQuery Version 1.0. If the version declaration is not
present, the version is presumed to be "1.0". An XQuery
implementation must raise a <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXQST0031" title=
"err:XQST0031">err:XQST0031</a>] when processing a <a title=
"module" href="#dt-module">module</a> labeled with a version that
the implementation does not support. It is the intent of the XQuery
working group to give later versions of this specification numbers
other than "1.0", but this intent does not indicate a commitment to
produce any future versions of XQuery, nor if any are produced, to
use any particular numbering scheme.</p>
<p>[<a name="dt-encoding-declaration" id="dt-encoding-declaration"
title="encoding declaration">Definition</a>: If present, a version
declaration may optionally include an <b>encoding declaration</b>.
The value of the string literal following the keyword
<code>encoding</code> is an encoding name, and must conform to the
definition of <code>EncName</code> specified in <a href="#XML">[XML
1.0]</a>[<a href="#ERRXQST0087" title=
"err:XQST0087">err:XQST0087</a>]. The purpose of an encoding
declaration is to allow the writer of a query to provide a string
that indicates how the query is encoded, such as
"<code>UTF-8</code>", "<code>UTF-16</code>", or
"<code>US-ASCII</code>".] Since the encoding of a query may change
as the query moves from one environment to another, there can be no
guarantee that the encoding declaration is correct.</p>
<p>The handling of an encoding declaration is <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>. If an
implementation has <em>a priori</em> knowledge of the encoding of a
query, it may use this knowledge and disregard the encoding
declaration. The semantics of a query are not affected by the
presence or absence of an encoding declaration.</p>
<p>If a version declaration is present, no <a href=
"#doc-xquery-Comment">Comment</a> may occur before the end of the
version declaration. If such a <a href=
"#doc-xquery-Comment">Comment</a> is present, the result is
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>The effect of a Comment before the end of a version declaration
is implementation-dependent because it may suppress query
processing by interfering with detection of the encoding
declaration.</p>
</div>
<p>The following examples illustrate version declarations:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
xquery version "1.0";
</pre></div>
</div>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
xquery version "1.0" encoding "utf-8";
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-module-declaration" id=
"id-module-declaration"></a>4.2 Module Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ModuleDecl" id=
"doc-xquery-ModuleDecl"></a>[5]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ModuleDecl" class=
"xquery">ModuleDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"module" "namespace" <a href=
"#prod-xquery-NCName">NCName</a> "=" <a href=
"#doc-xquery-URILiteral">URILiteral</a> <a href=
"#doc-xquery-Separator">Separator</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-module-declaration" id="dt-module-declaration"
title="module declaration">Definition</a>: A <b>module
declaration</b> serves to identify a <a title="module" href=
"#dt-module">module</a> as a <a title="library module" href=
"#dt-library-module">library module</a>. A module declaration
begins with the keyword <code>module</code> and contains a
namespace prefix and a <a href=
"#doc-xquery-URILiteral">URILiteral</a>.] The URILiteral must be of
nonzero length [<a href="#ERRXQST0088" title=
"err:XQST0088">err:XQST0088</a>]. The URILiteral identifies the
<a title="target namespace" href="#dt-target-namespace">target
namespace</a> of the library module, which is the namespace for all
variables and functions exported by the library module. The name of
every variable and function declared in a library module must have
a namespace URI that is the same as the target namespace of the
module; otherwise a <a title="static error" href=
"#dt-static-error">static error</a> is raised [<a href=
"#ERRXQST0048" title="err:XQST0048">err:XQST0048</a>]. In the
<a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> of the
library module, the namespace prefix specified in the module
declaration is bound to the module's target namespace.</p>
<p>The namespace prefix specified in a module declaration must not
be <code>xml</code> or <code>xmlns</code> [<a href="#ERRXQST0070"
title="err:XQST0070">err:XQST0070</a>], and must not be the same as
any namespace prefix bound in the same module by a <a title=
"schema import" href="#dt-schema-import">schema import</a>, by a
<a title="namespace declaration" href=
"#dt-namespace-declaration">namespace declaration</a>, or by a
<a title="module import" href="#dt-module-import">module import</a>
with a different target namespace [<a href="#ERRXQST0033" title=
"err:XQST0033">err:XQST0033</a>].</p>
<p>Any <a title="module" href="#dt-module">module</a> may import
one or more library modules by means of a <a title="module import"
href="#dt-module-import">module import</a> that specifies the
target namespace of the library modules to be imported. When a
module imports one or more library modules, the variables and
functions declared in the imported modules are added to the
<a title="static context" href="#dt-static-context">static
context</a> and (where applicable) to the <a title=
"dynamic context" href="#dt-dynamic-context">dynamic context</a> of
the importing module.</p>
<p>The following is an example of a module declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
module namespace math = "http://example.org/math-functions";
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-boundary-space-decls" id=
"id-boundary-space-decls"></a>4.3 Boundary-space Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-BoundarySpaceDecl" id=
"doc-xquery-BoundarySpaceDecl"></a>[11]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-BoundarySpaceDecl" class=
"xquery">BoundarySpaceDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "boundary-space" ("preserve" |
"strip")</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-boundary-space-decl" id="dt-boundary-space-decl"
title="boundary-space declaration">Definition</a>: A
<b>boundary-space declaration</b> sets the <a title=
"boundary-space policy" href=
"#dt-boundary-space-policy">boundary-space policy</a> in the
<a title="static context" href="#dt-static-context">static
context</a>, overriding any implementation-defined default.
Boundary-space policy controls whether <a title=
"boundary whitespace" href="#dt-boundary-whitespace">boundary
whitespace</a> is preserved by element constructors during
processing of the query.] If boundary-space policy is
<code>preserve</code>, boundary whitespace is preserved. If
boundary-space policy is <code>strip</code>, boundary whitespace is
stripped (deleted). A further discussion of whitespace in
constructed elements can be found in <a href=
"#id-whitespace"><b>3.7.1.4 Boundary Whitespace</b></a>.</p>
<p>The following example illustrates a boundary-space
declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare boundary-space preserve;
</pre></div>
</div>
<p>If a Prolog contains more than one boundary-space declaration, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXQST0068" title=
"err:XQST0068">err:XQST0068</a>].</p>
</div>
<div class="div2">
<h3><a name="id-default-collation-declaration" id=
"id-default-collation-declaration"></a>4.4 Default Collation
Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DefaultCollationDecl" id=
"doc-xquery-DefaultCollationDecl"></a>[19]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DefaultCollationDecl" class=
"xquery">DefaultCollationDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "default" "collation" <a href=
"#doc-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-default-collation-decl" id=
"dt-default-collation-decl" title=
"default collation declaration">Definition</a>: A <b>default
collation declaration</b> sets the value of the <a title=
"default collation" href="#dt-def-collation">default collation</a>
in the <a title="static context" href="#dt-static-context">static
context</a>, overriding any implementation-defined default.] The
default collation is the collation that is used by functions and
operators that require a collation if no other collation is
specified. For example, the <code>gt</code> operator on strings is
defined by a call to the <code>fn:compare</code> function, which
takes an optional collation parameter. Since the <code>gt</code>
operator does not specify a collation, the <code>fn:compare</code>
function implements <code>gt</code> by using the default
collation.</p>
<p>If neither the implementation nor the Prolog specifies a default
collation, the Unicode codepoint collation
(<code>http://www.w3.org/2005/xpath-functions/collation/codepoint</code>)
is used.</p>
<p>The following example illustrates a default collation
declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare default collation
         "http://example.org/languages/Icelandic";
</pre></div>
</div>
<p>If a default collation declaration specifies a collation by a
relative URI, that relative URI is resolved to an absolute URI
using the <a title="base URI" href="#dt-base-uri">base URI</a> in
the <a title="static context" href="#dt-static-context">static
context</a>. If a Prolog contains more than one default collation
declaration, or the value specified by a default collation
declaration (after resolution of a relative URI, if necessary) is
not present in <a title="statically known collations" href=
"#dt-static-collations">statically known collations</a>, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXQST0038" title=
"err:XQST0038">err:XQST0038</a>].</p>
</div>
<div class="div2">
<h3><a name="id-base-uri-decl" id="id-base-uri-decl"></a>4.5 Base
URI Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-BaseURIDecl" id=
"doc-xquery-BaseURIDecl"></a>[20]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-BaseURIDecl" class=
"xquery">BaseURIDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "base-uri" <a href=
"#doc-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-base-uri-decl" id="dt-base-uri-decl" title=
"base URI declaration">Definition</a>: A <b>base URI
declaration</b> specifies the <a title="base URI" href=
"#dt-base-uri">base URI</a> property of the <a title=
"static context" href="#dt-static-context">static context</a>. The
<a title="base URI" href="#dt-base-uri">base URI</a> property is
used when resolving relative URIs within a <a title="module" href=
"#dt-module">module</a>.] For example, the <code>fn:doc</code>
function resolves a relative URI using the base URI of the calling
module.</p>
<p>The following is an example of a base URI declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare base-uri "http://example.org";
</pre></div>
</div>
<p>If a Prolog contains more than one base URI declaration, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXQST0032" title=
"err:XQST0032">err:XQST0032</a>].</p>
<p>In the terminology of <a href="#RFC3986">[RFC3986]</a> Section
5.1, the URILiteral of the base URI declaration is considered to be
a "base URI embedded in content". If no base URI declaration is
present, the <a title="base URI" href="#dt-base-uri">base URI</a>
in the <a title="static context" href="#dt-static-context">static
context</a> is established according to the principles outlined in
<a href="#RFC3986">[RFC3986]</a> Section 5.1—that is, it defaults
first to the base URI of the encapsulating entity, then to the URI
used to retrieve the entity, and finally to an
implementation-defined default. If the URILiteral in the base URI
declaration is a relative URI, then it is made absolute by
resolving it with respect to this same hierarchy. For example, if
the URILiteral in the base URI declaration is
<code>../data/</code>, and the query is contained in a file whose
URI is <code>file:///C:/temp/queries/query.xq</code>, then the
<a title="base URI" href="#dt-base-uri">base URI</a> in the
<a title="static context" href="#dt-static-context">static
context</a> is <code>file:///C:/temp/data/</code>.</p>
<p>It is not intrinsically an error if this process fails to
establish an absolute base URI; however, the <a title="base URI"
href="#dt-base-uri">base URI</a> in the <a title="static context"
href="#dt-static-context">static context</a> is then <a title=
"undefined" href="#dt-undefined">undefined</a> [<a href=
"#ERRXPST0001" title="err:XPST0001">err:XPST0001</a>]. When the
base URI in the static context is <a title="undefined" href=
"#dt-undefined">undefined</a>, any attempt to use its value to
resolve a relative URI reference will result in an error [<a href=
"#ERRXPST0001" title="err:XPST0001">err:XPST0001</a>]. When the
base URI of a constructed node is taken from the base URI in the
static context and the latter is <a title="undefined" href=
"#dt-undefined">undefined</a>, then the base-uri property of the
constructed node is empty.</p>
</div>
<div class="div2">
<h3><a name="id-construction-declaration" id=
"id-construction-declaration"></a>4.6 Construction Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ConstructionDecl" id=
"doc-xquery-ConstructionDecl"></a>[25]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ConstructionDecl" class=
"xquery">ConstructionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "construction" ("strip" |
"preserve")</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-construction-decl" id="dt-construction-decl" title=
"construction declaration">Definition</a>: A <b>construction
declaration</b> sets the <a title="construction mode" href=
"#dt-construction-mode">construction mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a>,
overriding any implementation-defined default.] The construction
mode governs the behavior of element and document node
constructors. If construction mode is <code>preserve</code>, the
type of a constructed element node is <code>xs:anyType</code>, and
all attribute and element nodes copied during node construction
retain their original types. If construction mode is
<code>strip</code>, the type of a constructed element node is
<code>xs:untyped</code>; all element nodes copied during node
construction receive the type <code>xs:untyped</code>, and all
attribute nodes copied during node construction receive the type
<code>xs:untypedAtomic</code>.</p>
<p>The following example illustrates a construction
declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare construction strip;
</pre></div>
</div>
<p>If a Prolog specifies more than one construction declaration, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXQST0067" title=
"err:XQST0067">err:XQST0067</a>].</p>
</div>
<div class="div2">
<h3><a name="id-default-ordering-decl" id=
"id-default-ordering-decl"></a>4.7 Ordering Mode Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OrderingModeDecl" id=
"doc-xquery-OrderingModeDecl"></a>[14]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderingModeDecl" class=
"xquery">OrderingModeDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "ordering" ("ordered" |
"unordered")</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-ordering-mode-decl" id="dt-ordering-mode-decl"
title="ordering mode declaration">Definition</a>: An <b>ordering
mode declaration</b> sets the <a title="ordering mode" href=
"#dt-ordering-mode">ordering mode</a> in the <a title=
"static context" href="#dt-static-context">static context</a>,
overriding any implementation-defined default.] This ordering mode
applies to all expressions in a <a title="module" href=
"#dt-module">module</a> (including both the <a title="Prolog" href=
"#dt-prolog">Prolog</a> and the <a title="query body" href=
"#dt-queryBody">Query Body</a>, if any), unless overridden by an
<code>ordered</code> or <code>unordered</code> expression.</p>
<p><a title="ordering mode" href="#dt-ordering-mode">Ordering
mode</a> affects the behavior of <a title="path expression" href=
"#dt-path-expression">path expressions</a> that include a
"<code>/</code>" or "<code>//</code>" operator or an <a title=
"axis step" href="#dt-axis-step">axis step</a>; <code>union</code>,
<code>intersect</code>, and <code>except</code> expressions; and
FLWOR expressions that have no <code>order by</code> clause. If
ordering mode is <code>ordered</code>, node sequences returned by
path, <code>union</code>, <code>intersect</code>, and
<code>except</code> expressions are in <a title="document order"
href="#dt-document-order">document order</a>; otherwise the order
of these return sequences is <a title="implementation dependent"
href="#dt-implementation-dependent">implementation-dependent</a>.
The effect of ordering mode on FLWOR expressions is described in
<a href="#id-flwor-expressions"><b>3.8 FLWOR
Expressions</b></a>.</p>
<p>The following example illustrates an ordering mode
declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare ordering unordered;
</pre></div>
</div>
<p>If a Prolog contains more than one ordering mode declaration, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXQST0065" title=
"err:XQST0065">err:XQST0065</a>].</p>
</div>
<div class="div2">
<h3><a name="id-empty-order-decl" id="id-empty-order-decl"></a>4.8
Empty Order Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-EmptyOrderDecl" id=
"doc-xquery-EmptyOrderDecl"></a>[15]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-EmptyOrderDecl" class=
"xquery">EmptyOrderDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "default" "order" "empty" ("greatest" |
"least")</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-empty-order-decl" id="dt-empty-order-decl" title=
"empty order declaration">Definition</a>: An <b>empty order
declaration</b> sets the <a title=
"default order for empty sequences" href=
"#dt-default-empty-order">default order for empty sequences</a> in
the <a title="static context" href="#dt-static-context">static
context,</a> overriding any implementation-defined default. This
declaration controls the processing of empty sequences and
<code>NaN</code> values as ordering keys in an <code>order
by</code> clause in a FLWOR expression.] An individual <code>order
by</code> clause may override the default order for empty sequences
by specifying <code>empty greatest</code> or <code>empty
least</code>.</p>
<p>The following example illustrates an empty order
declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare default order empty least;
</pre></div>
</div>
<p>If a Prolog contains more than one empty order declaration, a
<a title="static error" href="#dt-static-error">static error</a> is
raised [<a href="#ERRXQST0069" title=
"err:XQST0069">err:XQST0069</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>It is important to distinguish an <a title=
"empty order declaration" href="#dt-empty-order-decl">empty order
declaration</a> from an <a title="ordering mode declaration" href=
"#dt-ordering-mode-decl">ordering mode declaration</a>. An
<a title="empty order declaration" href=
"#dt-empty-order-decl">empty order declaration</a> applies only
when an <code>order by</code> clause is present, and specifies how
empty sequences are treated by the <code>order by</code> clause
(unless overridden). An <a title="ordering mode declaration" href=
"#dt-ordering-mode-decl">ordering mode declaration</a>, on the
other hand, applies only in the absence of an <code>order by</code>
clause.</p>
</div>
</div>
<div class="div2">
<h3><a name="id-copy-namespaces-decl" id=
"id-copy-namespaces-decl"></a>4.9 Copy-Namespaces Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-CopyNamespacesDecl" id=
"doc-xquery-CopyNamespacesDecl"></a>[16]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CopyNamespacesDecl" class=
"xquery">CopyNamespacesDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "copy-namespaces" <a href=
"#doc-xquery-PreserveMode">PreserveMode</a> "," <a href=
"#doc-xquery-InheritMode">InheritMode</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-PreserveMode" id=
"doc-xquery-PreserveMode"></a>[17]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-PreserveMode" class=
"xquery">PreserveMode</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"preserve" | "no-preserve"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-InheritMode" id=
"doc-xquery-InheritMode"></a>[18]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-InheritMode" class=
"xquery">InheritMode</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"inherit" | "no-inherit"</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-copy-namespaces-decl" id="dt-copy-namespaces-decl"
title="copy-namespaces declaration">Definition</a>: A
<b>copy-namespaces declaration</b> sets the value of <a title=
"copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> in the
<a title="static context" href="#dt-static-context">static
context</a>, overriding any implementation-defined default.
Copy-namespaces mode controls the namespace bindings that are
assigned when an existing element node is copied by an element
constructor or document constructor.] Handling of namespace
bindings by element constructors is described in <a href=
"#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a>.</p>
<p>The following example illustrates a copy-namespaces
declaration:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare copy-namespaces preserve, no-inherit;
</pre></div>
</div>
<p>If a Prolog contains more than one copy-namespaces declaration,
a <a title="static error" href="#dt-static-error">static error</a>
is raised [<a href="#ERRXQST0055" title=
"err:XQST0055">err:XQST0055</a>].</p>
</div>
<div class="div2">
<h3><a name="id-schema-import" id="id-schema-import"></a>4.10
Schema Import</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-SchemaImport" id=
"doc-xquery-SchemaImport"></a>[21]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-SchemaImport" class=
"xquery">SchemaImport</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"import" "schema" <a href=
"#doc-xquery-SchemaPrefix">SchemaPrefix</a>? <a href=
"#doc-xquery-URILiteral">URILiteral</a> ("at" <a href=
"#doc-xquery-URILiteral">URILiteral</a> ("," <a href=
"#doc-xquery-URILiteral">URILiteral</a>)*)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-SchemaPrefix" id=
"doc-xquery-SchemaPrefix"></a>[22]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-SchemaPrefix" class=
"xquery">SchemaPrefix</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("namespace" <a href="#prod-xquery-NCName">NCName</a>
"=") | ("default" "element" "namespace")</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-schema-import" id="dt-schema-import" title=
"schema import">Definition</a>: A <b>schema import</b> imports the
element declarations, attribute declarations, and type definitions
from a schema into the <a title="in-scope schema definitions" href=
"#dt-issd">in-scope schema definitions</a>. <span>For each
user-defined atomic type in the schema, schema import also adds a
corresponding <a title="constructor function" href=
"#dt-constructor-function">constructor function</a>.</span> ] The
schema to be imported is identified by its <a title=
"target namespace" href="#dt-target-namespace">target
namespace</a>. The schema import may bind a namespace prefix to the
target namespace of the imported schema, or may declare that target
namespace to be the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a>. The
schema import may also provide optional hints for locating the
schema.</p>
<p>The namespace prefix specified in a schema import must not be
<code>xml</code> or <code>xmlns</code> [<a href="#ERRXQST0070"
title="err:XQST0070">err:XQST0070</a>], and must not be the same as
any namespace prefix bound in the same module by another schema
import, a <a title="module import" href="#dt-module-import">module
import</a>, a <a title="namespace declaration" href=
"#dt-namespace-declaration">namespace declaration</a>, or a
<a title="module import" href="#dt-module-import">module
declaration</a> [<a href="#ERRXQST0033" title=
"err:XQST0033">err:XQST0033</a>].</p>
<p>The first <a href="#doc-xquery-URILiteral">URILiteral</a> in a
schema import specifies the target namespace of the schema to be
imported. The URILiterals that follow the <code>at</code> keyword
are optional location hints, and can be interpreted or disregarded
in an implementation-dependent way. Multiple location hints might
be used to indicate more than one possible place to look for the
schema or multiple physical resources to be assembled to form the
schema.</p>
<p>A schema import that specifies a zero-length string as target
namespace is considered to import a schema that has no target
namespace. Such a schema import may not bind a namespace prefix
[<a href="#ERRXQST0057" title="err:XQST0057">err:XQST0057</a>], but
it may set the default element/type namespace to a zero-length
string (representing "no namespace"), thus enabling the definitions
in the imported namespace to be referenced. If the default
element/type namespace is not set to "no namespace", there is no
way to reference the definitions in an imported schema that has no
target namespace.</p>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0058" title=
"err:XQST0058">err:XQST0058</a>] if more than one schema import in
the same <a title="Prolog" href="#dt-prolog">Prolog</a> specifies
the same target namespace. It is a <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXQST0059" title=
"err:XQST0059">err:XQST0059</a>] if the implementation is not able
to process a schema import by finding a valid schema with the
specified target namespace. It is a <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXQST0035" title=
"err:XQST0035">err:XQST0035</a>] if multiple imported schemas, or
multiple physical resources within one schema, contain definitions
for the same name in the same symbol space (for example, two
definitions for the same element name, even if the definitions are
consistent). However, it is not an error to import the schema with
target namespace <code>http://www.w3.org/2001/XMLSchema</code>
(predeclared prefix <code>xs</code>), even though the built-in
types defined in this schema are implicitly included in the
<a title="in-scope schema type" href="#dt-is-types">in-scope schema
types.</a></p>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0012" title=
"err:XQST0012">err:XQST0012</a>] if the set of definitions
contained in all schemas imported by a Prolog do not satisfy the
conditions for schema validity specified in Sections 3 and 5 of
<a href="#XMLSchema">[XML Schema]</a> Part 1--i.e., each definition
must be valid, complete, and unique.</p>
<p>The following example imports a schema, specifying both its
target namespace and its location, and binding the prefix
<code>soap</code> to the target namespace:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
import schema namespace soap="http://www.w3.org/2003/05/soap-envelope"
at "http://www.w3.org/2003/05/soap-envelope/";
</pre></div>
</div>
<p>The following example imports a schema by specifying only its
target namespace, and makes it the default element/type
namespace:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
import schema default element namespace "http://example.org/abc";
</pre></div>
</div>
<p>The following example imports a schema that has no target
namespace, providing a location hint, and sets the default
element/type namespace to "no namespace" so that the definitions in
the imported schema can be referenced:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
import schema default element namespace "" 
at "http://example.org/xyz.xsd";
</pre></div>
</div>
<p>The following example imports a schema that has no target
namespace and sets the default element/type namespace to "no
namespace". Since no location hint is provided, it is up to the
implementation to find the schema to be imported.</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
import schema default element namespace "";
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-module-import" id="id-module-import"></a>4.11
Module Import</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ModuleImport" id=
"doc-xquery-ModuleImport"></a>[23]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ModuleImport" class=
"xquery">ModuleImport</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"import" "module" ("namespace" <a href=
"#prod-xquery-NCName">NCName</a> "=")? <a href=
"#doc-xquery-URILiteral">URILiteral</a> ("at" <a href=
"#doc-xquery-URILiteral">URILiteral</a> ("," <a href=
"#doc-xquery-URILiteral">URILiteral</a>)*)?</code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-module-import" id="dt-module-import" title=
"module import">Definition</a>: A <b>module import</b> imports the
function declarations and variable declarations from one or more
<a title="library module" href="#dt-library-module">library
modules</a> into the <a title="function signature" href=
"#dt-function-signature">function signatures</a> and <a title=
"in-scope variables" href="#dt-in-scope-variables">in-scope
variables</a> of the importing <a title="module" href=
"#dt-module">module</a>.] Each module import names a <a title=
"target namespace" href="#dt-target-namespace">target namespace</a>
and imports an <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> set of
modules that share this target namespace. The module import may
bind a namespace prefix to the target namespace, and it may provide
optional hints for locating the modules to be imported.</p>
<p>The namespace prefix specified in a module import must not be
<code>xml</code> or <code>xmlns</code> [<a href="#ERRXQST0070"
title="err:XQST0070">err:XQST0070</a>], and must not be the same as
any namespace prefix bound in the same module by another module
import, a <a title="schema import" href="#dt-schema-import">schema
import</a>, a <a title="namespace declaration" href=
"#dt-namespace-declaration">namespace declaration</a>, or a
<a title="module declaration" href="#dt-module-declaration">module
declaration</a> with a different target namespace [<a href=
"#ERRXQST0033" title="err:XQST0033">err:XQST0033</a>].</p>
<p>The first <a href="#doc-xquery-URILiteral">URILiteral</a> in a
module import must be of nonzero length [<a href="#ERRXQST0088"
title="err:XQST0088">err:XQST0088</a>], and specifies the target
namespace of the modules to be imported. The URILiterals that
follow the <code>at</code> keyword are optional location hints, and
can be interpreted or disregarded in an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> way.</p>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0047" title=
"err:XQST0047">err:XQST0047</a>] if more than one module import in
a <a title="Prolog" href="#dt-prolog">Prolog</a> specifies the same
target namespace. It is a <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXQST0059" title=
"err:XQST0059">err:XQST0059</a>] if the implementation is not able
to process a module import by finding a valid module definition
with the specified target namespace. It is a <a title=
"static error" href="#dt-static-error">static error</a> if the
<a title="expanded QName" href="#dt-expanded-qname">expanded
QName</a> and arity of a function declared in an imported module
are respectively equal to the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> and arity of a function
declared in the importing module or in another imported module
(even if the declarations are consistent) [<a href="#ERRXQST0034"
title="err:XQST0034">err:XQST0034</a>]. It is a <a title=
"static error" href="#dt-static-error">static error</a> if the
<a title="expanded QName" href="#dt-expanded-qname">expanded
QName</a> of a variable declared in an imported module is equal (as
defined by the <code>eq</code> operator) to the <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a> of a
variable declared in the importing module or in another imported
module (even if the declarations are consistent) [<a href=
"#ERRXQST0049" title="err:XQST0049">err:XQST0049</a>].</p>
<p>Each <a title="module" href="#dt-module">module</a> has its own
<a title="static context" href="#dt-static-context">static
context</a>. A <a title="module import" href=
"#dt-module-import">module import</a> imports only functions and
variable declarations; it does not import other objects from the
imported modules, such as <a title="in-scope schema definitions"
href="#dt-issd">in-scope schema definitions</a> or <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>. Module
imports are not transitive—that is, importing a module provides
access only to function and variable declarations contained
directly in the imported module. For example, if module A imports
module B, and module B imports module C, module A does not have
access to the functions and variables declared in module C.</p>
<p>A module may import its own target namespace (this is
interpreted as importing an <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> set of
other modules that share its target namespace.)</p>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0036" title=
"err:XQST0036">err:XQST0036</a>] to import a module if the
<a title="in-scope schema definitions" href="#dt-issd">in-scope
schema definitions</a> of the importing module do not include all
of the following:</p>
<ol class="enumar">
<li>
<p>An <a title="in-scope schema type" href="#dt-is-types">in-scope
schema type</a> for each type-name that appears:</p>
<ol class="enumla">
<li>
<p>in the type of a variable that is declared in the imported
module and referenced in the importing module, OR</p>
</li>
<li>
<p>in a parameter-type or result-type of a function that is
declared in the imported module and referenced in the importing
module.</p>
</li>
</ol>
</li>
<li>
<p>An <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declaration</a> for each
element-name <code>EN</code> such that:</p>
<ol class="enumla">
<li>
<p><code>schema-element(EN)</code> appears in the declared type of
a variable in the imported module, and that variable is referenced
in the importing module, OR</p>
</li>
<li>
<p><code>schema-element(EN)</code> appears in a parameter-type or
result-type of a function declared in the imported module, and that
function is referenced in the importing module.</p>
</li>
</ol>
</li>
<li>
<p>An <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declaration</a> for each
attribute-name <code>AN</code> such that:</p>
<ol class="enumla">
<li>
<p><code>schema-attribute(AN)</code> appears in the declared type
of a variable in the imported module, and that variable is
referenced in the importing module, OR</p>
</li>
<li>
<p><code>schema-attribute(AN)</code> appears in a parameter-type or
result-type of a function declared in the imported module, and that
function is referenced in the importing module.</p>
</li>
</ol>
</li>
</ol>
<p>To illustrate the above rules, suppose that a certain schema
defines a type named <code>triangle</code>. Suppose that a library
module imports the schema, binds its target namespace to the prefix
<code>geometry</code>, and declares a function with the following
<a title="function signature" href=
"#dt-function-signature">function signature</a>: <code>math:area($t
as geometry:triangle) as xs:double</code>. If a query wishes to use
this function, it must import <em>both</em> the library module and
the schema on which it is based. Importing the library module alone
would not provide access to the definition of the type
<code>geometry:triangle</code> used in the signature of the
<code>area</code> function.</p>
<p>[<a name="dt-module-directly-depends" id=
"dt-module-directly-depends" title=
"module directly depends">Definition</a>: A module M<sub>1</sub>
<b>directly depends</b> on another module M<sub>2</sub> (different
from M<sub>1</sub>) if a variable or function declared in
M<sub>1</sub> <a title="variable depends" href=
"#dt-variable-depends">depends</a> on a variable or function
declared in M<sub>2</sub>.] It is a <a title="static error" href=
"#dt-static-error">static error</a> [<a href="#ERRXQST0093" title=
"err:XQST0093">err:XQST0093</a>] to import a module M<sub>1</sub>
if there exists a sequence of modules M<sub>1</sub> ...
M<sub>i</sub> ... M<sub>1</sub> such that each module <a title=
"module directly depends" href=
"#dt-module-directly-depends">directly depends</a> on the next
module in the sequence (informally, if M<sub>1</sub> depends on
itself through some chain of module dependencies.)</p>
<p>The following example illustrates a module import:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
import module namespace math = "http://example.org/math-functions";
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-namespace-declaration" id=
"id-namespace-declaration"></a>4.12 Namespace Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-NamespaceDecl" id=
"doc-xquery-NamespaceDecl"></a>[10]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-NamespaceDecl" class=
"xquery">NamespaceDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "namespace" <a href=
"#prod-xquery-NCName">NCName</a> "=" <a href=
"#doc-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
</table>
<p>[<a name="dt-namespace-declaration" id=
"dt-namespace-declaration" title=
"namespace declaration">Definition</a>: A <b>namespace
declaration</b> declares a namespace prefix and associates it with
a namespace URI, adding the (prefix, URI) pair to the set of
<a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>.] The
namespace declaration is in scope throughout the query in which it
is declared, unless it is overridden by a <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a> in a
<a title="direct element constructor" href=
"#dt-direct-elem-const">direct element constructor</a>.</p>
<p>If the URILiteral part of a namespace declaration is a
zero-length string, any existing namespace binding for the given
prefix is removed from the <a title="statically known namespaces"
href="#dt-static-namespaces">statically known namespaces</a>. This
feature provides a way to remove predeclared namespace prefixes
such as <code>local</code>.</p>
<p>The following query illustrates a namespace declaration:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare namespace foo = "http://example.org";
&lt;foo:bar&gt; Lentils &lt;/foo:bar&gt;
</pre></div>
</div>
<p>In the query result, the newly created node is in the namespace
associated with the namespace URI
<code>http://example.org</code>.</p>
<p>The namespace prefix specified in a namespace declaration must
not be <code>xml</code> or <code>xmlns</code> [<a href=
"#ERRXQST0070" title="err:XQST0070">err:XQST0070</a>]. The
namespace URI specified in a namespace declaration must not be
<code>http://www.w3.org/XML/1998/namespace</code> or
<code>http://www.w3.org/2000/xmlns/</code> [<a href="#ERRXQST0070"
title="err:XQST0070">err:XQST0070</a>]. The namespace prefix
specified in a namespace declaration must not be the same as any
namespace prefix bound in the same module by a <a title=
"module import" href="#dt-module-import">module import</a>,
<a title="schema import" href="#dt-schema-import">schema
import</a>, <a title="module import" href=
"#dt-module-import">module declaration</a>, or another namespace
declaration [<a href="#ERRXQST0033" title=
"err:XQST0033">err:XQST0033</a>].</p>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXPST0081" title=
"err:XPST0081">err:XPST0081</a>] if an expression contains a QName
with a namespace prefix that is not in the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>.</p>
<p>XQuery has several predeclared namespace prefixes that are
present in the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> before each
query is processed. These prefixes may be used without an explicit
declaration. They may be overridden by <a title=
"namespace declaration" href="#dt-namespace-declaration">namespace
declarations</a> in a <a title="Prolog" href=
"#dt-prolog">Prolog</a> or by <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attributes</a> on
constructed elements (however, the prefix <code>xml</code> may not
be redeclared, and no other prefix may be bound to the namespace
URI associated with the prefix <code>xml</code> [<a href=
"#ERRXQST0070" title="err:XQST0070">err:XQST0070</a>]). The
predeclared namespace prefixes are as follows:</p>
<ul>
<li>
<p><code>xml = http://www.w3.org/XML/1998/namespace</code></p>
</li>
<li>
<p><code>xs = http://www.w3.org/2001/XMLSchema</code></p>
</li>
<li>
<p><code>xsi = http://www.w3.org/2001/XMLSchema-instance</code></p>
</li>
<li>
<p><code>fn = http://www.w3.org/2005/xpath-functions</code></p>
</li>
<li>
<p><code>local =
http://www.w3.org/2005/xquery-local-functions</code> (see <a href=
"#FunctionDeclns"><b>4.15 Function Declaration</b></a>.)</p>
</li>
</ul>
<p>Additional predeclared namespace prefixes may be added to the
<a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> by an
implementation.</p>
<p>When element or attribute names are compared, they are
considered identical if the local parts and namespace URIs match on
a codepoint basis. Namespace prefixes need not be identical for two
names to match, as illustrated by the following example:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare namespace xx = "http://example.org";

let $i := &lt;foo:bar xmlns:foo = "http://example.org"&gt;
              &lt;foo:bing&gt; Lentils &lt;/foo:bing&gt;
          &lt;/foo:bar&gt;
return $i/xx:bing
</pre></div>
</div>
<p>Although the namespace prefixes <code>xx</code> and
<code>foo</code> differ, both are bound to the namespace URI
<code>"http://example.org"</code>. Since <code>xx:bing</code> and
<code>foo:bing</code> have the same local name and the same
namespace URI, they match. The output of the above query is as
follows.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;foo:bing xmlns:foo = "http://example.org"&gt; Lentils &lt;/foo:bing&gt;
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-default-namespace" id=
"id-default-namespace"></a>4.13 Default Namespace Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-DefaultNamespaceDecl" id=
"doc-xquery-DefaultNamespaceDecl"></a>[12]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-DefaultNamespaceDecl" class=
"xquery">DefaultNamespaceDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "default" ("element" | "function") "namespace"
<a href="#doc-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
</table>
<p><b>Default namespace declarations</b> can be used in a <a title=
"Prolog" href="#dt-prolog">Prolog</a> to facilitate the use of
unprefixed QNames. The following kinds of default namespace
declarations are supported:</p>
<ul>
<li>
<p>A <b>default element/type namespace declaration</b> declares a
namespace URI that is associated with unprefixed names of elements
and types. This declaration is recorded as the <a title=
"default element/type namespace" href="#dt-def-elemtype-ns">default
element/type namespace</a> in the <a title="static context" href=
"#dt-static-context">static context</a>. A <a title="Prolog" href=
"#dt-prolog">Prolog</a> may contain at most one default
element/type namespace declaration [<a href="#ERRXQST0066" title=
"err:XQST0066">err:XQST0066</a>]. If the <a href=
"#doc-xquery-URILiteral">URILiteral</a> in a default element/type
namespace declaration is a zero-length string, the <a title=
"default element/type namespace" href="#dt-def-elemtype-ns">default
element/type namespace</a> is undeclared (set to "none"), and
unprefixed names of elements and types are considered to be in no
namespace. The following example illustrates the declaration of a
default namespace for elements and types:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare default element namespace "http://example.org/names";
</pre></div>
</div>
<p>A default element/type namespace declaration may be overridden
by a <a title="namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a> in a
<a title="direct element constructor" href=
"#dt-direct-elem-const">direct element constructor</a>.</p>
<p>If no default element/type namespace declaration is present,
unprefixed element and type names are in no namespace (however, an
implementation may define a different default as specified in
<a href="#id-xq-static-context-components"><b>C.1 Static Context
Components</b></a>.)</p>
</li>
<li>
<p>A <b>default function namespace declaration</b> declares a
namespace URI that is associated with unprefixed function names in
function calls and function declarations. This declaration is
recorded as the <a title="default function namespace" href=
"#dt-def-fn-ns">default function namespace</a> in the <a title=
"static context" href="#dt-static-context">static context</a>. A
<a title="Prolog" href="#dt-prolog">Prolog</a> may contain at most
one default function namespace declaration [<a href="#ERRXQST0066"
title="err:XQST0066">err:XQST0066</a>]. If the StringLiteral in a
default function namespace declaration is a zero-length string, the
default function namespace is undeclared (set to "none"). In that
case, any functions that are associated with a namespace can be
called only by using an explicit namespace prefix.</p>
<p>If no default function namespace declaration is present, the
default function namespace is the namespace of XPath/XQuery
functions, <code>http://www.w3.org/2005/xpath-functions</code>
(however, an implementation may define a different default as
specified in <a href="#id-xq-static-context-components"><b>C.1
Static Context Components</b></a>.)</p>
<p>The following example illustrates the declaration of a default
function namespace:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare default function namespace 
     "http://example.org/math-functions";
</pre></div>
</div>
<p>The effect of declaring a default function namespace is that all
functions in the default function namespace, including
implicitly-declared <a title="constructor function" href=
"#dt-constructor-function">constructor functions</a>, can be
invoked without specifying a namespace prefix. When a function call
uses a function name with no prefix, the local name of the function
must match a function (including implicitly-declared <a title=
"constructor function" href="#dt-constructor-function">constructor
functions</a>) in the default function namespace [<a href=
"#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Only <a title="constructor function" href=
"#dt-constructor-function">constructor functions</a> can be in no
namespace.</p>
</div>
</li>
</ul>
<p>Unprefixed attribute names and variable names are in no
namespace.</p>
</div>
<div class="div2">
<h3><a name="id-variable-declarations" id=
"id-variable-declarations"></a>4.14 Variable Declaration</h3>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-VarDecl" id=
"doc-xquery-VarDecl"></a>[24]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-VarDecl" class=
"xquery">VarDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "variable" "$" <a href=
"#prod-xquery-QName">QName</a> <a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a>? ((":=" <a href=
"#doc-xquery-ExprSingle">ExprSingle</a>) | "external")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e17286.doc-xquery-VarName" id=
"noid_d2e17286.doc-xquery-VarName"></a>[88]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-VarName" class=
"xquery">VarName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e17287.doc-xquery-TypeDeclaration" id=
"noid_d2e17287.doc-xquery-TypeDeclaration"></a>[118]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TypeDeclaration" class=
"xquery">TypeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"as" <a href=
"#doc-xquery-SequenceType">SequenceType</a></code></td>
</tr>
</tbody>
</table>
<p>A <b>variable declaration</b> adds the <a title="static type"
href="#dt-static-type">static type</a> of a variable to the
<a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a>, and may also add a
value for the variable to the <a title="variable values" href=
"#dt-variable-values">variable values</a>. If the <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a> of
the variable is equal (as defined by the <code>eq</code> operator)
to the name of another variable in <a title="in-scope variables"
href="#dt-in-scope-variables">in-scope variables</a>, a <a title=
"static error" href="#dt-static-error">static error</a> is raised
[<a href="#ERRXQST0049" title="err:XQST0049">err:XQST0049</a>].</p>
<p>If a variable declaration includes a type, that type is added to
the <a title="static context" href="#dt-static-context">static
context</a> as the type of the variable. If a variable declaration
includes an expression but not an explicit type, the type of the
variable is inferred from static analysis of the expression and is
added to the <a title="static context" href=
"#dt-static-context">static context</a>. If a variable declaration
includes both a type and an expression, the value returned by the
expression must match the declared type according to the rules for
<a title="SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>; otherwise a
<a title="type error" href="#dt-type-error">type error</a> is
raised [<a href="#ERRXPTY0004" title=
"err:XPTY0004">err:XPTY0004</a>].</p>
<p>[<a name="dt-initializing-expression" id=
"dt-initializing-expression" title=
"initializing expression">Definition</a>: If a variable declaration
includes an expression, the expression is called an <b>initializing
expression</b>.] The initializing expression for a given variable
must be evaluated before the evaluation of any expression that
references the variable. The <a title="static context" href=
"#dt-static-context">static context</a> for an initializing
expression includes all functions that are declared or imported
anywhere in the <a title="Prolog" href="#dt-prolog">Prolog</a>, but
it includes only those variables and namespaces that are declared
or imported earlier in the Prolog than the variable that is being
initialized. The context item, position, and size in the <a title=
"dynamic context" href="#dt-dynamic-context">dynamic context</a> of
the initializing expression have initial values as described in
<a href="#id-xq-evaluation-context-components"><b>C.2 Dynamic
Context Components</b></a>.</p>
<p>[<a name="dt-variable-depends" id="dt-variable-depends" title=
"variable depends">Definition</a>: A variable <code>$x</code>
<b>depends</b> on a variable <code>$y</code> or a function
<code>f2</code> if a reference to <code>$y</code> or
<code>f2</code> appears in the initializing expression of
<code>$x</code>, or if there exists a variable <code>$z</code> or a
function <code>f3</code> such that <code>$x</code> <a title=
"variable depends" href="#dt-variable-depends">depends</a> on
<code>$z</code> or <code>f3</code> and <code>$z</code> or
<code>f3</code> <a title="function depends" href=
"#dt-function-depends">depends</a> on <code>$y</code> or
<code>f2</code>.]</p>
<p>[<a name="dt-function-depends" id="dt-function-depends" title=
"function depends">Definition</a>: A function <code>f1</code>
<b>depends</b> on a variable <code>$y</code> or a function
<code>f2</code> if a reference to <code>$y</code> or
<code>f2</code> appears in the body of <code>f1</code>, or if there
exists a variable <code>$z</code> or a function <code>f3</code>
such that <code>f1</code> <a title="function depends" href=
"#dt-function-depends">depends</a> on <code>$z</code> or
<code>f3</code> and <code>$z</code> or <code>f3</code> <a title=
"variable depends" href="#dt-variable-depends">depends</a> on
<code>$y</code> or <code>f2</code>.]</p>
<p>If a variable <a title="variable depends" href=
"#dt-variable-depends">depends</a> on itself, a <a title=
"static error" href="#dt-static-error">static error</a> is raised
[<a href="#ERRXQST0054" title="err:XQST0054">err:XQST0054</a>].</p>
<p>If the variable declaration includes the keyword
<code>external</code>, a value must be provided for the variable by
the external environment before the query can be evaluated. If an
external variable declaration also includes a declared type, the
value provided by the external environment must match the declared
type according to the rules for <a title="SequenceType matching"
href="#dt-sequencetype-matching">SequenceType matching</a> (see
<a href="#id-consistency-constraints"><b>2.2.5 Consistency
Constraints</b></a>). If an external variable declaration does not
include a declared type, the type and a matching value must be
provided by the external environment at evaluation time. The
<a title="static type" href="#dt-static-type">static type</a> of
such a variable is considered to be <code>item()*</code>. Any
reference to a variable that was declared <code>external</code>,
but was not bound to a value by the external environment, raises a
dynamic error [<a href="#ERRXPDY0002" title=
"err:XPDY0002">err:XPDY0002</a>].</p>
<p>All variable names declared in a <a title="library module" href=
"#dt-library-module">library module</a> must (when expanded) be in
the <a title="target namespace" href="#dt-target-namespace">target
namespace</a> of the library module [<a href="#ERRXQST0048" title=
"err:XQST0048">err:XQST0048</a>]. When a library module is
imported, variables declared in the imported module are added to
the <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> of the importing
module.</p>
<p>Variable names that have no namespace prefix are in no
namespace. Variable declarations that have no namespace prefix may
appear only in a main module.</p>
<p>The term <b>variable declaration</b> always refers to a
declaration of a variable in a <a title="Prolog" href=
"#dt-prolog">Prolog</a>. The binding of a variable to a value in a
query expression, such as a FLWOR expression, is known as a
<b>variable binding</b>, and does not make the variable visible to
an importing module.</p>
<p>Here are some examples of variable declarations:</p>
<ul>
<li>
<p>The following declaration specifies both the type and the value
of a variable. This declaration causes the type
<code>xs:integer</code> to be associated with variable
<code>$x</code> in the <a title="static context" href=
"#dt-static-context">static context</a>, and the value
<code>7</code> to be associated with variable <code>$x</code> in
the <a title="dynamic context" href="#dt-dynamic-context">dynamic
context</a>.</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare variable $x as xs:integer := 7;
</pre></div>
</div>
</li>
<li>
<p>The following declaration specifies a value but not a type. The
<a title="static type" href="#dt-static-type">static type</a> of
the variable is inferred from the static type of its value. In this
case, the variable <code>$x</code> has a static type of
<code>xs:decimal</code>, inferred from its value which is 7.5.</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare variable $x := 7.5;
</pre></div>
</div>
</li>
<li>
<p>The following declaration specifies a type but not a value. The
keyword <code>external</code> indicates that the value of the
variable will be provided by the external environment. At
evaluation time, if the variable <code>$x</code> in the <a title=
"dynamic context" href="#dt-dynamic-context">dynamic context</a>
does not have a value of type <code>xs:integer</code>, a type error
is raised.</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare variable $x as xs:integer external;
</pre></div>
</div>
</li>
<li>
<p>The following declaration specifies neither a type nor a value.
It simply declares that the query depends on the existence of a
variable named <code>$x</code>, whose type and value will be
provided by the external environment. During query analysis, the
type of <code>$x</code> is considered to be <code>item()*</code>.
During query evaluation, the <a title="dynamic context" href=
"#dt-dynamic-context">dynamic context</a> must include a type and a
value for <code>$x</code>, and its value must be compatible with
its type.</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare variable $x external;
</pre></div>
</div>
</li>
<li>
<p>The following declaration, which might appear in a library
module, declares a variable whose name includes a namespace
prefix:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare variable $math:pi as xs:double := 3.14159E0;
</pre></div>
</div>
</li>
</ul>
</div>
<div class="div2">
<h3><a name="FunctionDeclns" id="FunctionDeclns"></a>4.15 Function
Declaration</h3>
<p>In addition to the built-in functions described in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>, XQuery allows users to declare
functions of their own. A function declaration specifies the name
of the function, the names and datatypes of the parameters, and the
datatype of the result. All datatypes are specified using the
syntax described in <a href="#id-types"><b>2.5 Types</b></a>. A
function declaration causes the declared function to be added to
the <a title="function signature" href=
"#dt-function-signature">function signatures</a> of the <a title=
"module" href="#dt-module">module</a> in which it appears.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-FunctionDecl" id=
"doc-xquery-FunctionDecl"></a>[26]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-FunctionDecl" class=
"xquery">FunctionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "function" <a href=
"#prod-xquery-QName">QName</a> "(" <a href=
"#doc-xquery-ParamList">ParamList</a>? ")" ("as" <a href=
"#doc-xquery-SequenceType">SequenceType</a>)? (<a href=
"#doc-xquery-EnclosedExpr">EnclosedExpr</a> |
"external")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-ParamList" id=
"doc-xquery-ParamList"></a>[27]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ParamList" class=
"xquery">ParamList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Param">Param</a> ("," <a href=
"#doc-xquery-Param">Param</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-Param" id=
"doc-xquery-Param"></a>[28]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Param" class=
"xquery">Param</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"$" <a href="#prod-xquery-QName">QName</a> <a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a>?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="noid_d2e17633.doc-xquery-TypeDeclaration" id=
"noid_d2e17633.doc-xquery-TypeDeclaration"></a>[118]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TypeDeclaration" class=
"xquery">TypeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"as" <a href=
"#doc-xquery-SequenceType">SequenceType</a></code></td>
</tr>
</tbody>
</table>
<p>A function declaration specifies whether a function is <a title=
"user-defined function" href="#dt-udf">user-defined</a> or
<a title="external function" href=
"#dt-external-function">external</a>. [<a name="dt-udf" id="dt-udf"
title="user-defined function">Definition</a>: For a <b>user-defined
function</b>, the function declaration includes an expression
called the <b>function body</b> that defines how the result of the
function is computed from its parameters.]. The <a title=
"static context" href="#dt-static-context">static context</a> for a
function body includes all functions that are declared or imported
anywhere in the <a title="Prolog" href="#dt-prolog">Prolog</a>, but
it includes only those variables and namespaces that are declared
or imported earlier in the Prolog than the function that is being
defined.</p>
<p>[<a name="dt-external-function" id="dt-external-function" title=
"external function">Definition</a>: <b>External functions</b> are
functions that are implemented outside the query environment.] For
example, an XQuery implementation might provide a set of external
functions in addition to the core function library described in
<a href="#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0
Functions and Operators (Second Edition)]</a>. External functions
are identified by the keyword <code>external</code>. The purpose of
a function declaration for an external function is to declare the
datatypes of the function parameters and result, for use in type
checking of the query that contains or imports the function
declaration.</p>
<p>An XQuery implementation may provide a facility whereby external
functions can be implemented using a host programming language, but
it is not required to do so. If such a facility is provided, the
protocols by which parameters are passed to an external function,
and the result of the function is returned to the invoking query,
are <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>. An XQuery
implementation may augment the type system of <a href=
"#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a> with additional types that are designed to facilitate
exchange of data with host programming languages, or it may provide
mechanisms for the user to define such types. For example, a type
might be provided that encapsulates an object returned by an
external function, such as an SQL database connection. These
additional types, if defined, are considered to be derived by
restriction from <code>xs:anyAtomicType</code>.</p>
<p>Every user-defined function must be in a namespace--that is,
every declared function name must (when expanded) have a non-null
namespace URI [<a href="#ERRXQST0060" title=
"err:XQST0060">err:XQST0060</a>]. If the function name in a
function declaration has no namespace prefix, it is considered to
be in the <a title="default function namespace" href=
"#dt-def-fn-ns">default function namespace</a>. Every function name
declared in a <a title="library module" href=
"#dt-library-module">library module</a> must (when expanded) be in
the <a title="target namespace" href="#dt-target-namespace">target
namespace</a> of the library module [<a href="#ERRXQST0048" title=
"err:XQST0048">err:XQST0048</a>]. It is a <a title="static error"
href="#dt-static-error">static error</a> [<a href="#ERRXQST0045"
title="err:XQST0045">err:XQST0045</a>] if the function name in a
function declaration (when expanded) is in any of the following
namespaces:</p>
<ul>
<li>
<p><code>http://www.w3.org/XML/1998/namespace</code></p>
</li>
<li>
<p><code>http://www.w3.org/2001/XMLSchema</code></p>
</li>
<li>
<p><code>http://www.w3.org/2001/XMLSchema-instance</code></p>
</li>
<li>
<p><code>http://www.w3.org/2005/xpath-functions</code></p>
</li>
</ul>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0034" title=
"err:XQST0034">err:XQST0034</a>] if the <a title="expanded QName"
href="#dt-expanded-qname">expanded QName</a> and arity (number of
arguments) of the declared function are equal (as defined by the
<code>eq</code> operator) to the <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> and arity of another
function in <a title="function signature" href=
"#dt-function-signature">function signatures</a>.</p>
<p>In order to allow main modules to declare functions for local
use within the module without defining a new namespace, XQuery
predefines the namespace prefix <code>local</code> to the namespace
<code>http://www.w3.org/2005/xquery-local-functions</code>. It is
suggested (but not required) that this namespace be used for
defining local functions.</p>
<p>If a function parameter is declared using a name but no type,
its default type is <code>item()*</code>. If the result type is
omitted from a function declaration, its default result type is
<code>item()*</code>.</p>
<p>The parameters of a function declaration are considered to be
variables whose scope is the function body. It is an <a title=
"static error" href="#dt-static-error">static error</a> [<a href=
"#ERRXQST0039" title="err:XQST0039">err:XQST0039</a>] for a
function declaration to have more than one parameter with the same
name. The type of a function parameter can be any type that can be
expressed as a <a title="sequence type" href=
"#dt-sequence-type">sequence type</a>.</p>
<p>The following example illustrates the declaration and use of a
local function that accepts a sequence of <code>employee</code>
elements, summarizes them by department, and returns a sequence of
<code>dept</code> elements.</p>
<ul>
<li>
<p>Using a function, prepare a summary of employees that are
located in Denver.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare function local:summary($emps as element(employee)*) 
   as element(dept)*
{
   for $d in fn:distinct-values($emps/deptno)
   let $e := $emps[deptno = $d]
   return
      &lt;dept&gt;
         &lt;deptno&gt;{$d}&lt;/deptno&gt;
         &lt;headcount&gt; {fn:count($e)} &lt;/headcount&gt;
         &lt;payroll&gt; {fn:sum($e/salary)} &lt;/payroll&gt;
      &lt;/dept&gt;
};

local:summary(fn:doc("acme_corp.xml")//employee[location = "Denver"])
</pre></div>
</div>
</li>
</ul>
<p>Rules for converting function arguments to their declared
parameter types, and for converting the result of a function to its
declared result type, are described in <a href=
"#id-function-calls"><b>3.1.5 Function Calls</b></a>.</p>
<p>A function declaration may be recursive—that is, it may
reference itself. Mutually recursive functions, whose bodies
reference each other, are also allowed. The following example
declares a recursive function that computes the maximum depth of a
node hierarchy, and calls the function to find the maximum depth of
a particular document. In its declaration, the user-declared
function <code>local:depth</code> calls the built-in functions
<code>empty</code> and <code>max</code>, which are in the default
function namespace.</p>
<ul>
<li>
<p>Find the maximum depth of the document named
<code>partlist.xml</code>.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
declare function local:depth($e as node()) as xs:integer
{
   (: A node with no children has depth 1 :)
   (: Otherwise, add 1 to max depth of children :)
   if (fn:empty($e/*)) then 1
   else fn:max(for $c in $e/* return local:depth($c)) + 1
};

local:depth(fn:doc("partlist.xml"))
</pre></div>
</div>
</li>
</ul>
<p>Since a <a title="constructor function" href=
"#dt-constructor-function">constructor function</a> is effectively
declared for every user-defined atomic type in the <a title=
"in-scope schema type" href="#dt-is-types">in-scope schema
types</a>, a <a title="static error" href="#dt-static-error">static
error</a> [<a href="#ERRXQST0034" title=
"err:XQST0034">err:XQST0034</a>] is raised if the Prolog attempts
to declare a single-parameter function with the same <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a> as
any of these types.</p>
</div>
<div class="div2">
<h3><a name="id-option-declaration" id=
"id-option-declaration"></a>4.16 Option Declaration</h3>
<p>[<a name="dt-option-declaration" id="dt-option-declaration"
title="option declaration">Definition</a>: An <b>option
declaration</b> declares an option that affects the behavior of a
particular implementation. Each option consists of an identifying
QName and a StringLiteral.]</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="doc-xquery-OptionDecl" id=
"doc-xquery-OptionDecl"></a>[13]&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OptionDecl" class=
"xquery">OptionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "option" <a href="#prod-xquery-QName">QName</a>
<a href="#doc-xquery-StringLiteral">StringLiteral</a></code></td>
</tr>
</tbody>
</table>
<p>Typically, a particular option will be recognized by some
implementations and not by others. The syntax is designed so that
option declarations can be successfully parsed by all
implementations.</p>
<p>The QName of an option must resolve to a namespace URI and local
name, using the <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a> [<a href=
"#ERRXPST0081" title="err:XPST0081">err:XPST0081</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>There is no default namespace for options.</p>
</div>
<p>Each implementation recognizes an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> set of
namespace URIs used to denote option declarations.</p>
<p>If the namespace part of the QName is not a namespace recognized
by the implementation as one used to denote option declarations,
then the option declaration is ignored.</p>
<p>Otherwise, the effect of the option declaration, including its
error behavior, is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>. For
example, if the local part of the QName is not recognized, or if
the StringLiteral does not conform to the rules defined by the
implementation for the particular option declaration, the
implementation may choose whether to report an error, ignore the
option declaration, or take some other action.</p>
<p>Implementations may impose rules on where particular option
declarations may appear relative to variable declarations and
function declarations, and the interpretation of an option
declaration may depend on its position.</p>
<p>An option declaration must not be used to change the syntax
accepted by the processor, or to suppress the detection of static
errors. However, it may be used without restriction to modify the
semantics of the query. The scope of the option declaration is
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>—for
example, an option declaration might apply to the whole query, to
the current module, or to the immediately following function
declaration.</p>
<p>The following examples illustrate several possible uses for
option declarations:</p>
<ul>
<li>
<p>This option declaration might be used to set a serialization
parameter:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare namespace exq = "http://example.org/XQueryImplementation";
declare option exq:output "encoding = iso-8859-1";
</pre></div>
</div>
</li>
<li>
<p>This option declaration might be used to specify how comments in
source documents returned by the <code>fn:doc()</code> function
should be handled:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare option exq:strip-comments "true";
</pre></div>
</div>
</li>
<li>
<p>This option declaration might be used to associate a namespace
used in function names with a Java class:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare namespace math = "http://example.org/MathLibrary";
declare option exq:java-class "math = java.lang.Math";
</pre></div>
</div>
</li>
</ul>
</div>
</div>
</div>
<div class="xquery">
<div class="div1">
<h2><a name="id-xquery-conformance" id=
"id-xquery-conformance"></a>5 Conformance</h2>
<p>This section defines the conformance criteria for an XQuery
processor. In this section, the following terms are used to
indicate the requirement levels defined in <a href="#RFC2119">[RFC
2119]</a>. [<a name="must" id="must" title="must">Definition</a>:
<b>MUST</b> means that the item is an absolute requirement of the
specification.] [<a name="may" id="may" title="may">Definition</a>:
<b>MAY</b> means that an item is truly optional.] [<a name="should"
id="should" title="should">Definition</a>: <b>SHOULD</b> means that
there may exist valid reasons in particular circumstances to ignore
a particular item, but the full implications must be understood and
carefully weighed before choosing a different course.]</p>
<p>An XQuery processor that claims to conform to this specification
<a title="must" href="#must">MUST</a> include a claim of Minimal
Conformance as defined in <a href="#id-minimal-conformance"><b>5.1
Minimal Conformance</b></a>. In addition to a claim of Minimal
Conformance, it <a title="may" href="#may">MAY</a> claim
conformance to one or more optional features defined in <a href=
"#id-conform-optional-features"><b>5.2 Optional
Features</b></a>.</p>
<div class="div2">
<h3><a name="id-minimal-conformance" id=
"id-minimal-conformance"></a>5.1 Minimal Conformance</h3>
<p>Minimal Conformance to this specification <a title="must" href=
"#must">MUST</a> include all of the following items:</p>
<ol class="enumar">
<li>
<p>Support for everything specified in this document except those
features specified in <a href=
"#id-conform-optional-features"><b>5.2 Optional Features</b></a> to
be optional. If an implementation does not provide a given optional
feature, it <a title="must" href="#must">MUST</a> implement any
requirements specified in <a href=
"#id-conform-optional-features"><b>5.2 Optional Features</b></a>
for implementations that do not provide that feature.</p>
</li>
<li>
<p>A definition of every item specified to be <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>, unless
that item is part of an optional feature that is not supported by
the implementation. A list of <a title="implementation defined"
href="#dt-implementation-defined">implementation-defined</a> items
can be found in <a href="#id-impl-defined-items"><b>D
Implementation-Defined Items</b></a>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Implementations are not required to define items specified to be
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
</div>
</li>
<li>
<p>Support for <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data
Model (Second Edition)]</a>, as specified in <a href=
"#id-data-model-conformance"><b>5.3 Data Model
Conformance</b></a>.</p>
</li>
<li>
<p>Support for all functions defined in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
</li>
</ol>
</div>
<div class="div2">
<h3><a name="id-conform-optional-features" id=
"id-conform-optional-features"></a>5.2 Optional Features</h3>
<div class="div3">
<h4><a name="id-schema-import-feature" id=
"id-schema-import-feature"></a>5.2.1 Schema Import Feature</h4>
<p>[<a name="dt-schema-import-feature" id=
"dt-schema-import-feature" title=
"schema import feature">Definition</a>: The <b>Schema Import
Feature</b> permits the query Prolog to contain a <a title=
"schema import" href="#dt-schema-import">schema import</a>.]</p>
<p>If an XQuery implementation does not support the Schema Import
Feature, it <a title="must" href="#must">MUST</a> raise a static
error [<a href="#ERRXQST0009" title=
"err:XQST0009">err:XQST0009</a>] if it encounters a schema
import.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>If an implementation does not support the Schema Import Feature,
the <a title="in-scope schema type" href="#dt-is-types">in-scope
schema types</a> consist only of built-in and <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> schema type
definitions, as described in <a href=
"#id-xq-static-context-components"><b>C.1 Static Context
Components</b></a>.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-schema-validation-feature" id=
"id-schema-validation-feature"></a>5.2.2 Schema Validation
Feature</h4>
<p>[<a name="dt-schema-validation-feature" id=
"dt-schema-validation-feature" title=
"schema validation feature">Definition</a>: The <b>Schema
Validation Feature</b> permits a query to contain a
<code>validate</code> expression (see <a href=
"#id-validate"><b>3.13 Validate Expressions</b></a>.)]</p>
<p>If an XQuery implementation does not support the Schema
Validation Feature, it <a title="must" href="#must">MUST</a> raise
a static error [<a href="#ERRXQST0075" title=
"err:XQST0075">err:XQST0075</a>] if it encounters a
<code>validate</code> expression.</p>
</div>
<div class="div3">
<h4><a name="id-static-typing-feature" id=
"id-static-typing-feature"></a>5.2.3 Static Typing Feature</h4>
<p>[<a name="dt-static-typing-feature" id=
"dt-static-typing-feature" title=
"static typing feature">Definition</a>: The <b>Static Typing
Feature</b> provides support for the static semantics defined in
<a href="#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal
Semantics (Second Edition)]</a>, and requires implementations to
detect and report <a title="type error" href="#dt-type-error">type
errors</a> during the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>.]</p>
<p>If an implementation does not support the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a>, but can nevertheless determine during the
static analysis phase that an expression, if evaluated, will
necessarily raise a type error at run time, the implementation
<a title="may" href="#may">MAY</a> raise that error during the
static analysis phase. The choice of whether to raise such an error
at analysis time is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation dependent</a>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>An implementation that does not support the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is not required to raise type errors during the
static analysis phase; however, it <a title="must" href=
"#must">MUST</a> detect and raise non-type-related static errors
during the static analysis phase.</p>
</div>
<div class="xquery">
<div class="div4">
<h5><a name="id-static-extensions" id=
"id-static-extensions"></a>5.2.3.1 Static Typing Extensions</h5>
<p>In some cases, the static typing rules defined in <a href=
"#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal Semantics
(Second Edition)]</a> are not very precise (see, for example, the
type inference rules for the ancestor axes—parent, ancestor, and
ancestor-or-self—and for the function <code>fn:root</code>). Some
implementations may wish to support more precise static typing
rules.</p>
<p>A conforming implementation that implements the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> <a title="may" href="#may">MAY</a> also provide
one or more <b>static typing extensions</b>. [<a name=
"dt-static-typing-extension" id="dt-static-typing-extension" title=
"static typing extension">Definition</a>: A <b>static typing
extension</b> is an <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> type
inference rule that infers a more precise static type than that
inferred by the type inference rules in <a href=
"#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal Semantics
(Second Edition)]</a>.] See <a href=
"http://www.w3.org/TR/xquery-semantics/#id-static-extensions">Section
6.1.1 Static Typing Extensions</a><sup><small>FS</small></sup> for
a formal definition of the constraints on static typing
extensions.</p>
</div>
</div>
</div>
<div class="div3">
<h4><a name="id-full-axis-feature" id=
"id-full-axis-feature"></a>5.2.4 Full Axis Feature</h4>
<p>[<a name="dt-optional-axis" id="dt-optional-axis" title=
"optional axis">Definition</a>: The following axes are designated
as <b>optional axes</b>: <code>ancestor</code>,
<code>ancestor-or-self</code>, <code>following</code>,
<code>following-sibling</code>, <code>preceding</code>, and
<code>preceding-sibling</code>.]</p>
<p>[<a name="dt-full-axis-feature" id="dt-full-axis-feature" title=
"Full Axis Feature">Definition</a>: A conforming XQuery
implementation that supports the <b>Full Axis Feature</b> <a title=
"must" href="#must">MUST</a> support all the <a title=
"optional axis" href="#dt-optional-axis">optional axes</a>.]</p>
<p>Conforming XQuery implementations that do not support the Full
Axis Feature <a title="may" href="#may">MAY</a> support one or more
optional axes; it is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> which
optional axes are supported by such implementations. A conforming
implementation that encounters a reference to an optional axis that
it does not support <a title="must" href="#must">MUST</a> raise a
<a title="static error" href="#dt-static-error">static error</a>
[<a href="#ERRXPST0010" title="err:XPST0010">err:XPST0010</a>].</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>XQuery does not recognize the <code>namespace</code> axis
(defined by XPath 1.0 and deprecated by XPath 2.0).</p>
</div>
</div>
<div class="div3">
<h4><a name="id-module-feature" id="id-module-feature"></a>5.2.5
Module Feature</h4>
<p>[<a name="dt-module-feature" id="dt-module-feature" title=
"module feature">Definition</a>: A conforming XQuery implementation
that supports the <b>Module Feature</b> allows a query Prolog to
contain a <b>Module Import</b> and allows <b>library modules</b> to
be created.]</p>
<p>A conforming implementation that does not support the Module
Feature <a title="must" href="#must">MUST</a> raise a <a title=
"static error" href="#dt-static-error">static error</a> [<a href=
"#ERRXQST0016" title="err:XQST0016">err:XQST0016</a>] if it
encounters a <a title="module declaration" href=
"#dt-module-declaration">module declaration</a> or a <a title=
"module import" href="#dt-module-import">module import</a>. Since a
<a title="module declaration" href="#dt-module-declaration">module
declaration</a> is required in a <a title="library module" href=
"#dt-library-module">library module</a>, the Module Feature is
required in order to create a <a title="library module" href=
"#dt-library-module">library module</a>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>In the absence of the Module Feature, each query consists of a
single <a title="main module" href="#dt-main-module">main
module</a>.</p>
</div>
</div>
<div class="div3">
<h4><a name="id-serialization-feature" id=
"id-serialization-feature"></a>5.2.6 Serialization Feature</h4>
<p>[<a name="dt-serialization-feature" id=
"dt-serialization-feature" title=
"serialization feature">Definition</a>: A conforming XQuery
implementation that supports the <b>Serialization Feature</b>
<a title="must" href="#must">MUST</a> provide means for serializing
the result of a query, as specified in <a href=
"#id-serialization"><b>2.2.4 Serialization</b></a>.]</p>
<p>A conforming XQuery implementation that supports the
Serialization Feature <a title="must" href="#must">MUST</a> conform
to <a href="#id-xq-serialization-parameters"><b>C.3 Serialization
Parameters</b></a>. The means by which serialization is invoked is
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
<p>If an error is raised during the serialization process as
specified in <a href="#serialization">[XSLT 2.0 and XQuery 1.0
Serialization (Second Edition)]</a>, an conforming XQuery
implementation <a title="must" href="#must">MUST</a> report the
error to the calling environment.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Not all implementations need to serialize. For instance, an
implementation might provide results via an XML API instead of
producing a textual representation.</p>
</div>
</div>
</div>
<div class="div2">
<h3><a name="id-data-model-conformance" id=
"id-data-model-conformance"></a>5.3 Data Model Conformance</h3>
<p>All XQuery implementations process data represented in the
<a title="data model" href="#dt-datamodel">data model</a> as
specified in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data
Model (Second Edition)]</a>. The data model specification relies on
languages such as XQuery to specify conformance criteria for the
data model in their respective environments, and suggests that the
following issues should be considered:</p>
<ol class="enumar">
<li>
<p><em>Support for normative construction from an infoset.</em> A
conforming implementation <a title="may" href="#may">MAY</a> choose
to claim conformance to <a href=
"http://www.w3.org/TR/xpath-datamodel/#const-infoset">Section 3.2
Construction from an Infoset</a><sup><small>DM</small></sup>, which
defines a normative way to construct an <a title="XDM instance"
href="#dt-data-model-instance">XDM instance</a> from an XML
document that is merely well-formed or is governed by a DTD.</p>
</li>
<li>
<p><em>Support for normative construction from a PSVI.</em> A
conforming implementation <a title="may" href="#may">MAY</a> choose
to claim conformance to <a href=
"http://www.w3.org/TR/xpath-datamodel/#const-psvi">Section 3.3
Construction from a PSVI</a><sup><small>DM</small></sup>, which
defines a normative way to construct an <a title="XDM instance"
href="#dt-data-model-instance">XDM instance</a> from an XML
document that is governed by a W3C XML Schema.</p>
</li>
<li>
<p><em>Support for XML 1.0 and XML 1.1.</em> The <a href=
"#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a> supports either <a href="#XML">[XML 1.0]</a> or
<a href="#XML1.1">[XML 1.1]</a>. In XQuery, the choice of which XML
version to support is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
<p>At the time of writing there is no published version of XML
Schema that references the XML 1.1 specifications. This means that
datatypes such as <code>xs:NCName</code> and <code>xs:ID</code> are
constrained by the XML 1.0 rules. It is recommended that an XQuery
1.0 processor should implement defined by later versions of XML
Schema as they become available.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>For suggestions on processing XML 1.1 documents, see <a href=
"#xml11schema10">[XML 1.1 and Schema 1.0]</a>.</p>
</div>
</li>
<li>
<p><em>Ranges of data values.</em> In XQuery, the following limits
are <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>:</p>
<ol class="enumla">
<li>
<p>For the <code>xs:decimal</code> type, the maximum number of
decimal digits (<code>totalDigits</code> facet) (must be at least
18).</p>
</li>
<li>
<p>For the types <code>xs:date</code>, <code>xs:time</code>,
<code>xs:dateTime</code>, <code>xs:gYear</code>, and
<code>xs:gYearMonth</code>: the maximum value of the year component
and the maximum number of fractional second digits (must be at
least 3).</p>
</li>
<li>
<p>For the <code>xs:duration type</code>: the maximum absolute
values of the years, months, days, hours, minutes, and seconds
components.</p>
</li>
<li>
<p>For the <code>xs:yearMonthDuration</code> type: the maximum
absolute value, expressed as an integer number of months.</p>
</li>
<li>
<p>For the <code>xs:dayTimeDuration</code> type: the maximum
absolute value, expressed as a decimal number of seconds.</p>
</li>
<li>
<p>For the types <code>xs:string</code>, <code>xs:hexBinary</code>,
<code>xs:base64Binary</code>, <code>xs:QName</code>,
<code>xs:anyURI</code>, <code>xs:NOTATION</code>, and types derived
from them: limitations (if any) imposed by the implementation on
lengths of values.</p>
</li>
</ol>
<p>The limits listed above need not be fixed, but may depend on
environmental factors such as system resources. For example, the
length of a value of type <code>xs:string</code> may be limited by
available memory.</p>
</li>
</ol>
</div>
<div class="xquery">
<div class="div2">
<h3><a name="id-syntax-extensions" id=
"id-syntax-extensions"></a>5.4 Syntax Extensions</h3>
<p>Any syntactic extensions to XQuery are <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>. The effect
of syntactic extensions, including their error behavior, is
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>. Syntactic
extensions may be used without restriction to modify the semantics
of a XQuery expression.</p>
</div>
</div>
</div>
</div>
</div>
<div class="back">
<div class="div1">
<h2><a name="nt-bnf" id="nt-bnf"></a>A XQuery Grammar</h2>
<div class="div2">
<h3><a name="id-grammar" id="id-grammar"></a>A.1 EBNF</h3>
<p>The grammar of XQuery uses the same simple Extended Backus-Naur
Form (EBNF) notation as <a href="#XML">[XML 1.0]</a> with the
following minor differences.</p>
<ul>
<li>
<p>All named symbols have a name that begins with an uppercase
letter.</p>
</li>
<li>
<p>It adds a notation for referring to productions in external
specs.</p>
</li>
<li>
<p>Comments or extra-grammatical constraints on grammar productions
are between '/*' and '*/' symbols.</p>
<ul>
<li>
<p>A 'xgc:' prefix is an extra-grammatical constraint, the details
of which are explained in <a href=
"#extra-grammatical-constraints"><b>A.1.2 Extra-grammatical
Constraints</b></a></p>
</li>
<li>
<p>A 'ws:' prefix explains the whitespace rules for the production,
the details of which are explained in <a href=
"#whitespace-rules"><b>A.2.4 Whitespace Rules</b></a></p>
</li>
<li>
<p>A 'gn:' prefix means a 'Grammar Note', and is meant as a
clarification for parsing rules, and is explained in <a href=
"#notes-on-parsing"><b>A.1.3 Grammar Notes</b></a>. These notes are
not normative.</p>
</li>
</ul>
</li>
</ul>
<p>The terminal symbols for this grammar include the quoted strings
used in the production rules below, and the terminal symbols
defined in section <a href="#terminal-symbols"><b>A.2.1 Terminal
Symbols</b></a>.</p>
<p>The EBNF notation is described in more detail in <a href=
"#EBNFNotation"><b>A.1.1 Notation</b></a>.</p>
<p>To increase readability, the EBNF in the main body of this
document omits some of these notational features. This appendix is
the normative version of the EBNF.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Module" id=
"prod-xquery-Module"></a>[1]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Module">Module</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-VersionDecl">VersionDecl</a>?
(<a href="#prod-xquery-LibraryModule">LibraryModule</a> | <a href=
"#prod-xquery-MainModule">MainModule</a>)</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-VersionDecl" id=
"prod-xquery-VersionDecl"></a>[2]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-VersionDecl">VersionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"xquery" "version" <a href=
"#prod-xquery-StringLiteral">StringLiteral</a> ("encoding" <a href=
"#prod-xquery-StringLiteral">StringLiteral</a>)? <a href=
"#prod-xquery-Separator">Separator</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-MainModule" id=
"prod-xquery-MainModule"></a>[3]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-MainModule">MainModule</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Prolog">Prolog</a> <a href=
"#prod-xquery-QueryBody">QueryBody</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-LibraryModule" id=
"prod-xquery-LibraryModule"></a>[4]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-LibraryModule">LibraryModule</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ModuleDecl">ModuleDecl</a> <a href=
"#prod-xquery-Prolog">Prolog</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ModuleDecl" id=
"prod-xquery-ModuleDecl"></a>[5]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ModuleDecl">ModuleDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"module" "namespace" <a href=
"#prod-xquery-NCName">NCName</a> "=" <a href=
"#prod-xquery-URILiteral">URILiteral</a> <a href=
"#prod-xquery-Separator">Separator</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Prolog" id=
"prod-xquery-Prolog"></a>[6]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Prolog">Prolog</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>((<a href=
"#prod-xquery-DefaultNamespaceDecl">DefaultNamespaceDecl</a> |
<a href="#prod-xquery-Setter">Setter</a> | <a href=
"#prod-xquery-NamespaceDecl">NamespaceDecl</a> | <a href=
"#prod-xquery-Import">Import</a>) <a href=
"#prod-xquery-Separator">Separator</a>)* ((<a href=
"#prod-xquery-VarDecl">VarDecl</a> | <a href=
"#prod-xquery-FunctionDecl">FunctionDecl</a> | <a href=
"#prod-xquery-OptionDecl">OptionDecl</a>) <a href=
"#prod-xquery-Separator">Separator</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Setter" id=
"prod-xquery-Setter"></a>[7]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Setter">Setter</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-BoundarySpaceDecl">BoundarySpaceDecl</a> | <a href=
"#prod-xquery-DefaultCollationDecl">DefaultCollationDecl</a> |
<a href="#prod-xquery-BaseURIDecl">BaseURIDecl</a> | <a href=
"#prod-xquery-ConstructionDecl">ConstructionDecl</a> | <a href=
"#prod-xquery-OrderingModeDecl">OrderingModeDecl</a> | <a href=
"#prod-xquery-EmptyOrderDecl">EmptyOrderDecl</a> | <a href=
"#prod-xquery-CopyNamespacesDecl">CopyNamespacesDecl</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Import" id=
"prod-xquery-Import"></a>[8]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Import">Import</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-SchemaImport">SchemaImport</a> |
<a href="#prod-xquery-ModuleImport">ModuleImport</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Separator" id=
"prod-xquery-Separator"></a>[9]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Separator">Separator</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>";"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-NamespaceDecl" id=
"prod-xquery-NamespaceDecl"></a>[10]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-NamespaceDecl">NamespaceDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "namespace" <a href=
"#prod-xquery-NCName">NCName</a> "=" <a href=
"#prod-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-BoundarySpaceDecl" id=
"prod-xquery-BoundarySpaceDecl"></a>[11]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-BoundarySpaceDecl">BoundarySpaceDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "boundary-space" ("preserve" |
"strip")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DefaultNamespaceDecl" id=
"prod-xquery-DefaultNamespaceDecl"></a>[12]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DefaultNamespaceDecl">DefaultNamespaceDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "default" ("element" | "function") "namespace"
<a href="#prod-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OptionDecl" id=
"prod-xquery-OptionDecl"></a>[13]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OptionDecl">OptionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "option" <a href="#prod-xquery-QName">QName</a>
<a href="#prod-xquery-StringLiteral">StringLiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrderingModeDecl" id=
"prod-xquery-OrderingModeDecl"></a>[14]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OrderingModeDecl">OrderingModeDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "ordering" ("ordered" |
"unordered")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-EmptyOrderDecl" id=
"prod-xquery-EmptyOrderDecl"></a>[15]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-EmptyOrderDecl">EmptyOrderDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "default" "order" "empty" ("greatest" |
"least")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CopyNamespacesDecl" id=
"prod-xquery-CopyNamespacesDecl"></a>[16]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CopyNamespacesDecl">CopyNamespacesDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "copy-namespaces" <a href=
"#prod-xquery-PreserveMode">PreserveMode</a> "," <a href=
"#prod-xquery-InheritMode">InheritMode</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PreserveMode" id=
"prod-xquery-PreserveMode"></a>[17]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PreserveMode">PreserveMode</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"preserve" | "no-preserve"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-InheritMode" id=
"prod-xquery-InheritMode"></a>[18]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-InheritMode">InheritMode</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"inherit" | "no-inherit"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DefaultCollationDecl" id=
"prod-xquery-DefaultCollationDecl"></a>[19]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DefaultCollationDecl">DefaultCollationDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "default" "collation" <a href=
"#prod-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-BaseURIDecl" id=
"prod-xquery-BaseURIDecl"></a>[20]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-BaseURIDecl">BaseURIDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "base-uri" <a href=
"#prod-xquery-URILiteral">URILiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-SchemaImport" id=
"prod-xquery-SchemaImport"></a>[21]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-SchemaImport">SchemaImport</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"import" "schema" <a href=
"#prod-xquery-SchemaPrefix">SchemaPrefix</a>? <a href=
"#prod-xquery-URILiteral">URILiteral</a> ("at" <a href=
"#prod-xquery-URILiteral">URILiteral</a> ("," <a href=
"#prod-xquery-URILiteral">URILiteral</a>)*)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-SchemaPrefix" id=
"prod-xquery-SchemaPrefix"></a>[22]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-SchemaPrefix">SchemaPrefix</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("namespace" <a href="#prod-xquery-NCName">NCName</a>
"=") | ("default" "element" "namespace")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ModuleImport" id=
"prod-xquery-ModuleImport"></a>[23]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ModuleImport">ModuleImport</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"import" "module" ("namespace" <a href=
"#prod-xquery-NCName">NCName</a> "=")? <a href=
"#prod-xquery-URILiteral">URILiteral</a> ("at" <a href=
"#prod-xquery-URILiteral">URILiteral</a> ("," <a href=
"#prod-xquery-URILiteral">URILiteral</a>)*)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-VarDecl" id=
"prod-xquery-VarDecl"></a>[24]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-VarDecl">VarDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "variable" "$" <a href=
"#prod-xquery-QName">QName</a> <a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a>? ((":=" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a>) | "external")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ConstructionDecl" id=
"prod-xquery-ConstructionDecl"></a>[25]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ConstructionDecl">ConstructionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "construction" ("strip" |
"preserve")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-FunctionDecl" id=
"prod-xquery-FunctionDecl"></a>[26]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-FunctionDecl">FunctionDecl</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"declare" "function" <a href=
"#prod-xquery-QName">QName</a> "(" <a href=
"#prod-xquery-ParamList">ParamList</a>? ")" ("as" <a href=
"#prod-xquery-SequenceType">SequenceType</a>)? (<a href=
"#prod-xquery-EnclosedExpr">EnclosedExpr</a> |
"external")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ParamList" id=
"prod-xquery-ParamList"></a>[27]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ParamList">ParamList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Param">Param</a> ("," <a href=
"#prod-xquery-Param">Param</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Param" id=
"prod-xquery-Param"></a>[28]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Param">Param</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"$" <a href="#prod-xquery-QName">QName</a> <a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a>?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-EnclosedExpr" id=
"prod-xquery-EnclosedExpr"></a>[29]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-EnclosedExpr">EnclosedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"{" <a href="#prod-xquery-Expr">Expr</a> "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-QueryBody" id=
"prod-xquery-QueryBody"></a>[30]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-QueryBody">QueryBody</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Expr">Expr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Expr" id=
"prod-xquery-Expr"></a>[31]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Expr">Expr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ExprSingle">ExprSingle</a> (","
<a href="#prod-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ExprSingle" id=
"prod-xquery-ExprSingle"></a>[32]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ExprSingle">ExprSingle</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-FLWORExpr">FLWORExpr</a><br />
| <a href="#prod-xquery-QuantifiedExpr">QuantifiedExpr</a><br />
| <a href="#prod-xquery-TypeswitchExpr">TypeswitchExpr</a><br />
| <a href="#prod-xquery-IfExpr">IfExpr</a><br />
| <a href="#prod-xquery-OrExpr">OrExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-FLWORExpr" id=
"prod-xquery-FLWORExpr"></a>[33]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-FLWORExpr">FLWORExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-ForClause">ForClause</a> |
<a href="#prod-xquery-LetClause">LetClause</a>)+ <a href=
"#prod-xquery-WhereClause">WhereClause</a>? <a href=
"#prod-xquery-OrderByClause">OrderByClause</a>? "return" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ForClause" id=
"prod-xquery-ForClause"></a>[34]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ForClause">ForClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"for" "$" <a href="#prod-xquery-VarName">VarName</a>
<a href="#prod-xquery-TypeDeclaration">TypeDeclaration</a>?
<a href="#prod-xquery-PositionalVar">PositionalVar</a>? "in"
<a href="#prod-xquery-ExprSingle">ExprSingle</a> ("," "$" <a href=
"#prod-xquery-VarName">VarName</a> <a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a>? <a href=
"#prod-xquery-PositionalVar">PositionalVar</a>? "in" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PositionalVar" id=
"prod-xquery-PositionalVar"></a>[35]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PositionalVar">PositionalVar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"at" "$" <a href=
"#prod-xquery-VarName">VarName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-LetClause" id=
"prod-xquery-LetClause"></a>[36]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-LetClause">LetClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"let" "$" <a href="#prod-xquery-VarName">VarName</a>
<a href="#prod-xquery-TypeDeclaration">TypeDeclaration</a>? ":="
<a href="#prod-xquery-ExprSingle">ExprSingle</a> ("," "$" <a href=
"#prod-xquery-VarName">VarName</a> <a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a>? ":=" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-WhereClause" id=
"prod-xquery-WhereClause"></a>[37]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-WhereClause">WhereClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"where" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrderByClause" id=
"prod-xquery-OrderByClause"></a>[38]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OrderByClause">OrderByClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(("order" "by") | ("stable" "order" "by")) <a href=
"#prod-xquery-OrderSpecList">OrderSpecList</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrderSpecList" id=
"prod-xquery-OrderSpecList"></a>[39]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OrderSpecList">OrderSpecList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-OrderSpec">OrderSpec</a> (","
<a href="#prod-xquery-OrderSpec">OrderSpec</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrderSpec" id=
"prod-xquery-OrderSpec"></a>[40]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-OrderSpec">OrderSpec</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ExprSingle">ExprSingle</a> <a href=
"#prod-xquery-OrderModifier">OrderModifier</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrderModifier" id=
"prod-xquery-OrderModifier"></a>[41]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OrderModifier">OrderModifier</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("ascending" | "descending")? ("empty" ("greatest" |
"least"))? ("collation" <a href=
"#prod-xquery-URILiteral">URILiteral</a>)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-QuantifiedExpr" id=
"prod-xquery-QuantifiedExpr"></a>[42]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-QuantifiedExpr">QuantifiedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("some" | "every") "$" <a href=
"#prod-xquery-VarName">VarName</a> <a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a>? "in" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a> ("," "$" <a href=
"#prod-xquery-VarName">VarName</a> <a href=
"#prod-xquery-TypeDeclaration">TypeDeclaration</a>? "in" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a>)* "satisfies" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-TypeswitchExpr" id=
"prod-xquery-TypeswitchExpr"></a>[43]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-TypeswitchExpr">TypeswitchExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"typeswitch" "(" <a href="#prod-xquery-Expr">Expr</a> ")"
<a href="#prod-xquery-CaseClause">CaseClause</a>+ "default" ("$"
<a href="#prod-xquery-VarName">VarName</a>)? "return" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CaseClause" id=
"prod-xquery-CaseClause"></a>[44]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CaseClause">CaseClause</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"case" ("$" <a href="#prod-xquery-VarName">VarName</a>
"as")? <a href="#prod-xquery-SequenceType">SequenceType</a>
"return" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-IfExpr" id=
"prod-xquery-IfExpr"></a>[45]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-IfExpr">IfExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"if" "(" <a href="#prod-xquery-Expr">Expr</a> ")" "then"
<a href="#prod-xquery-ExprSingle">ExprSingle</a> "else" <a href=
"#prod-xquery-ExprSingle">ExprSingle</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrExpr" id=
"prod-xquery-OrExpr"></a>[46]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-OrExpr">OrExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AndExpr">AndExpr</a> ( "or"
<a href="#prod-xquery-AndExpr">AndExpr</a> )*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AndExpr" id=
"prod-xquery-AndExpr"></a>[47]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AndExpr">AndExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ComparisonExpr">ComparisonExpr</a>
( "and" <a href="#prod-xquery-ComparisonExpr">ComparisonExpr</a>
)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ComparisonExpr" id=
"prod-xquery-ComparisonExpr"></a>[48]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ComparisonExpr">ComparisonExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-RangeExpr">RangeExpr</a> (
(<a href="#prod-xquery-ValueComp">ValueComp</a><br />
| <a href="#prod-xquery-GeneralComp">GeneralComp</a><br />
| <a href="#prod-xquery-NodeComp">NodeComp</a>) <a href=
"#prod-xquery-RangeExpr">RangeExpr</a> )?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-RangeExpr" id=
"prod-xquery-RangeExpr"></a>[49]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-RangeExpr">RangeExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AdditiveExpr">AdditiveExpr</a> (
"to" <a href="#prod-xquery-AdditiveExpr">AdditiveExpr</a>
)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AdditiveExpr" id=
"prod-xquery-AdditiveExpr"></a>[50]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AdditiveExpr">AdditiveExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-MultiplicativeExpr">MultiplicativeExpr</a> ( ("+" |
"-") <a href=
"#prod-xquery-MultiplicativeExpr">MultiplicativeExpr</a>
)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-MultiplicativeExpr" id=
"prod-xquery-MultiplicativeExpr"></a>[51]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-MultiplicativeExpr">MultiplicativeExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-UnionExpr">UnionExpr</a> ( ("*" |
"div" | "idiv" | "mod") <a href=
"#prod-xquery-UnionExpr">UnionExpr</a> )*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-UnionExpr" id=
"prod-xquery-UnionExpr"></a>[52]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-UnionExpr">UnionExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-IntersectExceptExpr">IntersectExceptExpr</a> (
("union" | "|") <a href=
"#prod-xquery-IntersectExceptExpr">IntersectExceptExpr</a>
)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-IntersectExceptExpr" id=
"prod-xquery-IntersectExceptExpr"></a>[53]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-IntersectExceptExpr">IntersectExceptExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-InstanceofExpr">InstanceofExpr</a>
( ("intersect" | "except") <a href=
"#prod-xquery-InstanceofExpr">InstanceofExpr</a> )*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-InstanceofExpr" id=
"prod-xquery-InstanceofExpr"></a>[54]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-InstanceofExpr">InstanceofExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-TreatExpr">TreatExpr</a> (
"instance" "of" <a href=
"#prod-xquery-SequenceType">SequenceType</a> )?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-TreatExpr" id=
"prod-xquery-TreatExpr"></a>[55]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-TreatExpr">TreatExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CastableExpr">CastableExpr</a> (
"treat" "as" <a href="#prod-xquery-SequenceType">SequenceType</a>
)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CastableExpr" id=
"prod-xquery-CastableExpr"></a>[56]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CastableExpr">CastableExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-CastExpr">CastExpr</a> ( "castable"
"as" <a href="#prod-xquery-SingleType">SingleType</a>
)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CastExpr" id=
"prod-xquery-CastExpr"></a>[57]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-CastExpr">CastExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-UnaryExpr">UnaryExpr</a> ( "cast"
"as" <a href="#prod-xquery-SingleType">SingleType</a>
)?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-UnaryExpr" id=
"prod-xquery-UnaryExpr"></a>[58]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-UnaryExpr">UnaryExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("-" | "+")* <a href=
"#prod-xquery-ValueExpr">ValueExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ValueExpr" id=
"prod-xquery-ValueExpr"></a>[59]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ValueExpr">ValueExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ValidateExpr">ValidateExpr</a> |
<a href="#prod-xquery-PathExpr">PathExpr</a> | <a href=
"#prod-xquery-ExtensionExpr">ExtensionExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-GeneralComp" id=
"prod-xquery-GeneralComp"></a>[60]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-GeneralComp">GeneralComp</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"=" | "!=" | "&lt;" | "&lt;=" | "&gt;" |
"&gt;="</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ValueComp" id=
"prod-xquery-ValueComp"></a>[61]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ValueComp">ValueComp</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"eq" | "ne" | "lt" | "le" | "gt" | "ge"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-NodeComp" id=
"prod-xquery-NodeComp"></a>[62]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-NodeComp">NodeComp</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"is" | "&lt;&lt;" | "&gt;&gt;"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ValidateExpr" id=
"prod-xquery-ValidateExpr"></a>[63]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ValidateExpr">ValidateExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"validate" <a href=
"#prod-xquery-ValidationMode">ValidationMode</a>? "{" <a href=
"#prod-xquery-Expr">Expr</a> "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ValidationMode" id=
"prod-xquery-ValidationMode"></a>[64]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ValidationMode">ValidationMode</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"lax" | "strict"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ExtensionExpr" id=
"prod-xquery-ExtensionExpr"></a>[65]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ExtensionExpr">ExtensionExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Pragma">Pragma</a>+ "{" <a href=
"#prod-xquery-Expr">Expr</a>? "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Pragma" id=
"prod-xquery-Pragma"></a>[66]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Pragma">Pragma</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"(#" <a href="#prod-xquery-S">S</a>? <a href=
"#prod-xquery-QName">QName</a> (<a href="#prod-xquery-S">S</a>
<a href="#prod-xquery-PragmaContents">PragmaContents</a>)?
"#)"</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PragmaContents" id=
"prod-xquery-PragmaContents"></a>[67]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PragmaContents">PragmaContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>* - (Char* '#)'
Char*))</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PathExpr" id=
"prod-xquery-PathExpr"></a>[68]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-PathExpr">PathExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("/" <a href=
"#prod-xquery-RelativePathExpr">RelativePathExpr</a>?)<br />
| ("//" <a href=
"#prod-xquery-RelativePathExpr">RelativePathExpr</a>)<br />
| <a href=
"#prod-xquery-RelativePathExpr">RelativePathExpr</a></code></td>
<td><i>/* <a href="#parse-note-leading-lone-slash">xgs:
leading-lone-slash</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-RelativePathExpr" id=
"prod-xquery-RelativePathExpr"></a>[69]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-RelativePathExpr">RelativePathExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-StepExpr">StepExpr</a> (("/" |
"//") <a href="#prod-xquery-StepExpr">StepExpr</a>)*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-StepExpr" id=
"prod-xquery-StepExpr"></a>[70]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-StepExpr">StepExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-FilterExpr">FilterExpr</a> |
<a href="#prod-xquery-AxisStep">AxisStep</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AxisStep" id=
"prod-xquery-AxisStep"></a>[71]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-AxisStep">AxisStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-ReverseStep">ReverseStep</a> |
<a href="#prod-xquery-ForwardStep">ForwardStep</a>) <a href=
"#prod-xquery-PredicateList">PredicateList</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ForwardStep" id=
"prod-xquery-ForwardStep"></a>[72]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ForwardStep">ForwardStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-ForwardAxis">ForwardAxis</a>
<a href="#prod-xquery-NodeTest">NodeTest</a>) | <a href=
"#prod-xquery-AbbrevForwardStep">AbbrevForwardStep</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ForwardAxis" id=
"prod-xquery-ForwardAxis"></a>[73]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ForwardAxis">ForwardAxis</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("child" "::")<br />
| ("descendant" "::")<br />
| ("attribute" "::")<br />
| ("self" "::")<br />
| ("descendant-or-self" "::")<br />
| ("following-sibling" "::")<br />
| ("following" "::")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AbbrevForwardStep" id=
"prod-xquery-AbbrevForwardStep"></a>[74]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AbbrevForwardStep">AbbrevForwardStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"@"? <a href=
"#prod-xquery-NodeTest">NodeTest</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ReverseStep" id=
"prod-xquery-ReverseStep"></a>[75]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ReverseStep">ReverseStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-ReverseAxis">ReverseAxis</a>
<a href="#prod-xquery-NodeTest">NodeTest</a>) | <a href=
"#prod-xquery-AbbrevReverseStep">AbbrevReverseStep</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ReverseAxis" id=
"prod-xquery-ReverseAxis"></a>[76]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ReverseAxis">ReverseAxis</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("parent" "::")<br />
| ("ancestor" "::")<br />
| ("preceding-sibling" "::")<br />
| ("preceding" "::")<br />
| ("ancestor-or-self" "::")</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AbbrevReverseStep" id=
"prod-xquery-AbbrevReverseStep"></a>[77]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AbbrevReverseStep">AbbrevReverseStep</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>".."</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-NodeTest" id=
"prod-xquery-NodeTest"></a>[78]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-NodeTest">NodeTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-KindTest">KindTest</a> | <a href=
"#prod-xquery-NameTest">NameTest</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-NameTest" id=
"prod-xquery-NameTest"></a>[79]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-NameTest">NameTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a> | <a href=
"#prod-xquery-Wildcard">Wildcard</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Wildcard" id=
"prod-xquery-Wildcard"></a>[80]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Wildcard">Wildcard</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"*"<br />
| (<a href="#prod-xquery-NCName">NCName</a> ":" "*")<br />
| ("*" ":" <a href="#prod-xquery-NCName">NCName</a>)</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-FilterExpr" id=
"prod-xquery-FilterExpr"></a>[81]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-FilterExpr">FilterExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-PrimaryExpr">PrimaryExpr</a>
<a href="#prod-xquery-PredicateList">PredicateList</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PredicateList" id=
"prod-xquery-PredicateList"></a>[82]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PredicateList">PredicateList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-Predicate">Predicate</a>*</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Predicate" id=
"prod-xquery-Predicate"></a>[83]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Predicate">Predicate</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"[" <a href="#prod-xquery-Expr">Expr</a> "]"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PrimaryExpr" id=
"prod-xquery-PrimaryExpr"></a>[84]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PrimaryExpr">PrimaryExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Literal">Literal</a> | <a href=
"#prod-xquery-VarRef">VarRef</a> | <a href=
"#prod-xquery-ParenthesizedExpr">ParenthesizedExpr</a> | <a href=
"#prod-xquery-ContextItemExpr">ContextItemExpr</a> | <a href=
"#prod-xquery-FunctionCall">FunctionCall</a> | <a href=
"#prod-xquery-OrderedExpr">OrderedExpr</a> | <a href=
"#prod-xquery-UnorderedExpr">UnorderedExpr</a> | <a href=
"#prod-xquery-Constructor">Constructor</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Literal" id=
"prod-xquery-Literal"></a>[85]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Literal">Literal</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-NumericLiteral">NumericLiteral</a>
| <a href=
"#prod-xquery-StringLiteral">StringLiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-NumericLiteral" id=
"prod-xquery-NumericLiteral"></a>[86]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-NumericLiteral">NumericLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-IntegerLiteral">IntegerLiteral</a>
| <a href="#prod-xquery-DecimalLiteral">DecimalLiteral</a> |
<a href="#prod-xquery-DoubleLiteral">DoubleLiteral</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-VarRef" id=
"prod-xquery-VarRef"></a>[87]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-VarRef">VarRef</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"$" <a href=
"#prod-xquery-VarName">VarName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-VarName" id=
"prod-xquery-VarName"></a>[88]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-VarName">VarName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ParenthesizedExpr" id=
"prod-xquery-ParenthesizedExpr"></a>[89]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ParenthesizedExpr">ParenthesizedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"(" <a href="#prod-xquery-Expr">Expr</a>? ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ContextItemExpr" id=
"prod-xquery-ContextItemExpr"></a>[90]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ContextItemExpr">ContextItemExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"."</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OrderedExpr" id=
"prod-xquery-OrderedExpr"></a>[91]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OrderedExpr">OrderedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"ordered" "{" <a href="#prod-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-UnorderedExpr" id=
"prod-xquery-UnorderedExpr"></a>[92]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-UnorderedExpr">UnorderedExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"unordered" "{" <a href="#prod-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-FunctionCall" id=
"prod-xquery-FunctionCall"></a>[93]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-FunctionCall">FunctionCall</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a> "(" (<a href=
"#prod-xquery-ExprSingle">ExprSingle</a> ("," <a href=
"#prod-xquery-ExprSingle">ExprSingle</a>)*)? ")"</code></td>
<td><i>/* <a href="#parse-note-reserved-function-names">xgs:
reserved-function-names</a> */</i></td>
</tr>
<tr valign="baseline">
<td></td>
<td></td>
<td></td>
<td></td>
<td><i>/* <a href="#parse-note-parens">gn: parens</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Constructor" id=
"prod-xquery-Constructor"></a>[94]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-Constructor">Constructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DirectConstructor">DirectConstructor</a><br />
| <a href=
"#prod-xquery-ComputedConstructor">ComputedConstructor</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirectConstructor" id=
"prod-xquery-DirectConstructor"></a>[95]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirectConstructor">DirectConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DirElemConstructor">DirElemConstructor</a><br />
| <a href=
"#prod-xquery-DirCommentConstructor">DirCommentConstructor</a><br />

| <a href=
"#prod-xquery-DirPIConstructor">DirPIConstructor</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirElemConstructor" id=
"prod-xquery-DirElemConstructor"></a>[96]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirElemConstructor">DirElemConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;" <a href="#prod-xquery-QName">QName</a> <a href=
"#prod-xquery-DirAttributeList">DirAttributeList</a> ("/&gt;" |
("&gt;" <a href="#prod-xquery-DirElemContent">DirElemContent</a>*
"&lt;/" <a href="#prod-xquery-QName">QName</a> <a href=
"#prod-xquery-S">S</a>? "&gt;"))</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirAttributeList" id=
"prod-xquery-DirAttributeList"></a>[97]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirAttributeList">DirAttributeList</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-S">S</a> (<a href=
"#prod-xquery-QName">QName</a> <a href="#prod-xquery-S">S</a>? "="
<a href="#prod-xquery-S">S</a>? <a href=
"#prod-xquery-DirAttributeValue">DirAttributeValue</a>)?)*</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirAttributeValue" id=
"prod-xquery-DirAttributeValue"></a>[98]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirAttributeValue">DirAttributeValue</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>('"' (<a href="#prod-xquery-EscapeQuot">EscapeQuot</a> |
<a href=
"#prod-xquery-QuotAttrValueContent">QuotAttrValueContent</a>)*
'"')<br />
| ("'" (<a href="#prod-xquery-EscapeApos">EscapeApos</a> | <a href=
"#prod-xquery-AposAttrValueContent">AposAttrValueContent</a>)*
"'")</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-QuotAttrValueContent" id=
"prod-xquery-QuotAttrValueContent"></a>[99]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-QuotAttrValueContent">QuotAttrValueContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-QuotAttrContentChar">QuotAttrContentChar</a><br />
| <a href=
"#prod-xquery-CommonContent">CommonContent</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AposAttrValueContent" id=
"prod-xquery-AposAttrValueContent"></a>[100]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AposAttrValueContent">AposAttrValueContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AposAttrContentChar">AposAttrContentChar</a><br />
| <a href=
"#prod-xquery-CommonContent">CommonContent</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirElemContent" id=
"prod-xquery-DirElemContent"></a>[101]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirElemContent">DirElemContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DirectConstructor">DirectConstructor</a><br />
| <a href="#prod-xquery-CDataSection">CDataSection</a><br />
| <a href="#prod-xquery-CommonContent">CommonContent</a><br />
| <a href=
"#prod-xquery-ElementContentChar">ElementContentChar</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CommonContent" id=
"prod-xquery-CommonContent"></a>[102]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CommonContent">CommonContent</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-PredefinedEntityRef">PredefinedEntityRef</a> |
<a href="#prod-xquery-CharRef">CharRef</a> | "{{" | "}}" | <a href=
"#prod-xquery-EnclosedExpr">EnclosedExpr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirCommentConstructor" id=
"prod-xquery-DirCommentConstructor"></a>[103]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirCommentConstructor">DirCommentConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;!--" <a href=
"#prod-xquery-DirCommentContents">DirCommentContents</a>
"--&gt;"</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirCommentContents" id=
"prod-xquery-DirCommentContents"></a>[104]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirCommentContents">DirCommentContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>((<a href="#prod-xquery-Char">Char</a> - '-') | ('-'
(<a href="#prod-xquery-Char">Char</a> - '-')))*</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirPIConstructor" id=
"prod-xquery-DirPIConstructor"></a>[105]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirPIConstructor">DirPIConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;?" <a href="#prod-xquery-PITarget">PITarget</a>
(<a href="#prod-xquery-S">S</a> <a href=
"#prod-xquery-DirPIContents">DirPIContents</a>)?
"?&gt;"</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DirPIContents" id=
"prod-xquery-DirPIContents"></a>[106]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DirPIContents">DirPIContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>* - (Char* '?&gt;'
Char*))</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CDataSection" id=
"prod-xquery-CDataSection"></a>[107]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CDataSection">CDataSection</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&lt;![CDATA[" <a href=
"#prod-xquery-CDataSectionContents">CDataSectionContents</a>
"]]&gt;"</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CDataSectionContents" id=
"prod-xquery-CDataSectionContents"></a>[108]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CDataSectionContents">CDataSectionContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>* - (Char* ']]&gt;'
Char*))</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ComputedConstructor" id=
"prod-xquery-ComputedConstructor"></a>[109]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ComputedConstructor">ComputedConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-CompDocConstructor">CompDocConstructor</a><br />
| <a href=
"#prod-xquery-CompElemConstructor">CompElemConstructor</a><br />
| <a href=
"#prod-xquery-CompAttrConstructor">CompAttrConstructor</a><br />
| <a href=
"#prod-xquery-CompTextConstructor">CompTextConstructor</a><br />
| <a href=
"#prod-xquery-CompCommentConstructor">CompCommentConstructor</a><br />

| <a href=
"#prod-xquery-CompPIConstructor">CompPIConstructor</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CompDocConstructor" id=
"prod-xquery-CompDocConstructor"></a>[110]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompDocConstructor">CompDocConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"document" "{" <a href="#prod-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CompElemConstructor" id=
"prod-xquery-CompElemConstructor"></a>[111]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompElemConstructor">CompElemConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"element" (<a href="#prod-xquery-QName">QName</a> | ("{"
<a href="#prod-xquery-Expr">Expr</a> "}")) "{" <a href=
"#prod-xquery-ContentExpr">ContentExpr</a>? "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ContentExpr" id=
"prod-xquery-ContentExpr"></a>[112]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ContentExpr">ContentExpr</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Expr">Expr</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CompAttrConstructor" id=
"prod-xquery-CompAttrConstructor"></a>[113]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompAttrConstructor">CompAttrConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"attribute" (<a href="#prod-xquery-QName">QName</a> |
("{" <a href="#prod-xquery-Expr">Expr</a> "}")) "{" <a href=
"#prod-xquery-Expr">Expr</a>? "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CompTextConstructor" id=
"prod-xquery-CompTextConstructor"></a>[114]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompTextConstructor">CompTextConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"text" "{" <a href="#prod-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CompCommentConstructor" id=
"prod-xquery-CompCommentConstructor"></a>[115]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompCommentConstructor">CompCommentConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"comment" "{" <a href="#prod-xquery-Expr">Expr</a>
"}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CompPIConstructor" id=
"prod-xquery-CompPIConstructor"></a>[116]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CompPIConstructor">CompPIConstructor</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"processing-instruction" (<a href=
"#prod-xquery-NCName">NCName</a> | ("{" <a href=
"#prod-xquery-Expr">Expr</a> "}")) "{" <a href=
"#prod-xquery-Expr">Expr</a>? "}"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-SingleType" id=
"prod-xquery-SingleType"></a>[117]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-SingleType">SingleType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AtomicType">AtomicType</a>
"?"?</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-TypeDeclaration" id=
"prod-xquery-TypeDeclaration"></a>[118]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-TypeDeclaration">TypeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"as" <a href=
"#prod-xquery-SequenceType">SequenceType</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-SequenceType" id=
"prod-xquery-SequenceType"></a>[119]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-SequenceType">SequenceType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("empty-sequence" "(" ")")<br />
| (<a href="#prod-xquery-ItemType">ItemType</a> <a href=
"#prod-xquery-OccurrenceIndicator">OccurrenceIndicator</a>?)</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-OccurrenceIndicator" id=
"prod-xquery-OccurrenceIndicator"></a>[120]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"?" | "*" | "+"</code></td>
<td><i>/* <a href="#parse-note-occurrence-indicators">xgs:
occurrence-indicators</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ItemType" id=
"prod-xquery-ItemType"></a>[121]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-ItemType">ItemType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-KindTest">KindTest</a> | ("item"
"(" ")") | <a href=
"#prod-xquery-AtomicType">AtomicType</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AtomicType" id=
"prod-xquery-AtomicType"></a>[122]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AtomicType">AtomicType</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-KindTest" id=
"prod-xquery-KindTest"></a>[123]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-KindTest">KindTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-DocumentTest">DocumentTest</a><br />
| <a href="#prod-xquery-ElementTest">ElementTest</a><br />
| <a href="#prod-xquery-AttributeTest">AttributeTest</a><br />
| <a href=
"#prod-xquery-SchemaElementTest">SchemaElementTest</a><br />
| <a href=
"#prod-xquery-SchemaAttributeTest">SchemaAttributeTest</a><br />
| <a href="#prod-xquery-PITest">PITest</a><br />
| <a href="#prod-xquery-CommentTest">CommentTest</a><br />
| <a href="#prod-xquery-TextTest">TextTest</a><br />
| <a href="#prod-xquery-AnyKindTest">AnyKindTest</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AnyKindTest" id=
"prod-xquery-AnyKindTest"></a>[124]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AnyKindTest">AnyKindTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"node" "(" ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DocumentTest" id=
"prod-xquery-DocumentTest"></a>[125]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DocumentTest">DocumentTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"document-node" "(" (<a href=
"#prod-xquery-ElementTest">ElementTest</a> | <a href=
"#prod-xquery-SchemaElementTest">SchemaElementTest</a>)?
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-TextTest" id=
"prod-xquery-TextTest"></a>[126]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-TextTest">TextTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"text" "(" ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CommentTest" id=
"prod-xquery-CommentTest"></a>[127]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CommentTest">CommentTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"comment" "(" ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PITest" id=
"prod-xquery-PITest"></a>[128]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-PITest">PITest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"processing-instruction" "(" (<a href=
"#prod-xquery-NCName">NCName</a> | <a href=
"#prod-xquery-StringLiteral">StringLiteral</a>)? ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AttributeTest" id=
"prod-xquery-AttributeTest"></a>[129]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AttributeTest">AttributeTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"attribute" "(" (<a href=
"#prod-xquery-AttribNameOrWildcard">AttribNameOrWildcard</a> (","
<a href="#prod-xquery-TypeName">TypeName</a>)?)? ")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AttribNameOrWildcard" id=
"prod-xquery-AttribNameOrWildcard"></a>[130]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AttribNameOrWildcard">AttribNameOrWildcard</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-AttributeName">AttributeName</a> |
"*"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-SchemaAttributeTest" id=
"prod-xquery-SchemaAttributeTest"></a>[131]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-SchemaAttributeTest">SchemaAttributeTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"schema-attribute" "(" <a href=
"#prod-xquery-AttributeDeclaration">AttributeDeclaration</a>
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AttributeDeclaration" id=
"prod-xquery-AttributeDeclaration"></a>[132]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AttributeDeclaration">AttributeDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-AttributeName">AttributeName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ElementTest" id=
"prod-xquery-ElementTest"></a>[133]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ElementTest">ElementTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"element" "(" (<a href=
"#prod-xquery-ElementNameOrWildcard">ElementNameOrWildcard</a> (","
<a href="#prod-xquery-TypeName">TypeName</a> "?"?)?)?
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ElementNameOrWildcard" id=
"prod-xquery-ElementNameOrWildcard"></a>[134]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ElementNameOrWildcard">ElementNameOrWildcard</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-ElementName">ElementName</a> |
"*"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-SchemaElementTest" id=
"prod-xquery-SchemaElementTest"></a>[135]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-SchemaElementTest">SchemaElementTest</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"schema-element" "(" <a href=
"#prod-xquery-ElementDeclaration">ElementDeclaration</a>
")"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ElementDeclaration" id=
"prod-xquery-ElementDeclaration"></a>[136]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ElementDeclaration">ElementDeclaration</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-ElementName">ElementName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AttributeName" id=
"prod-xquery-AttributeName"></a>[137]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AttributeName">AttributeName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ElementName" id=
"prod-xquery-ElementName"></a>[138]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ElementName">ElementName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-TypeName" id=
"prod-xquery-TypeName"></a>[139]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-TypeName">TypeName</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-QName">QName</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-URILiteral" id=
"prod-xquery-URILiteral"></a>[140]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-URILiteral">URILiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"#prod-xquery-StringLiteral">StringLiteral</a></code></td>
</tr>
</tbody>
</table>
<div class="div3">
<h4><a name="EBNFNotation" id="EBNFNotation"></a>A.1.1
Notation</h4>
<p>The following definitions will be helpful in defining precisely
this exposition.</p>
<p>[<a name="symbol" id="symbol" title="symbol">Definition</a>:
Each rule in the grammar defines one <b>symbol</b>, using the
following format:</p>
<div class="exampleInner">
<pre>
symbol ::= expression
</pre></div>
<p>]</p>
<p>[<a name="terminal" id="terminal" title=
"terminal">Definition</a>: A <b>terminal</b> is a symbol or string
or pattern that can appear in the right-hand side of a rule, but
never appears on the left hand side in the main grammar, although
it may appear on the left-hand side of a rule in the grammar for
terminals.] The following constructs are used to match strings of
one or more characters in a terminal:</p>
<dl>
<dt class="label">[a-zA-Z]</dt>
<dd>
<p>matches any <a href="#prod-xquery-Char">Char</a> with a value in
the range(s) indicated (inclusive).</p>
</dd>
<dt class="label">[abc]</dt>
<dd>
<p>matches any <a href="#prod-xquery-Char">Char</a> with a value
among the characters enumerated.</p>
</dd>
<dt class="label">[^abc]</dt>
<dd>
<p>matches any <a href="#prod-xquery-Char">Char</a> with a value
not among the characters given.</p>
</dd>
<dt class="label">"string"</dt>
<dd>
<p>matches the sequence of characters that appear inside the double
quotes.</p>
</dd>
<dt class="label">'string'</dt>
<dd>
<p>matches the sequence of characters that appear inside the single
quotes.</p>
</dd>
<dt class="label">
[http://www.w3.org/TR/REC-example/#NT-Example]</dt>
<dd>
<p>matches any string matched by the production defined in the
external specification as per the provided reference.</p>
</dd>
</dl>
<p>Patterns (including the above constructs) can be combined with
grammatical operators to form more complex patterns, matching more
complex sets of character strings. In the examples that follow, A
and B represent (sub-)patterns.</p>
<dl>
<dt class="label">(A)</dt>
<dd>
<p><code>A</code> is treated as a unit and may be combined as
described in this list.</p>
</dd>
<dt class="label">A?</dt>
<dd>
<p>matches <code>A</code> or nothing; optional <code>A</code>.</p>
</dd>
<dt class="label">A B</dt>
<dd>
<p>matches <code>A</code> followed by <code>B</code>. This operator
has higher precedence than alternation; thus <code>A B | C D</code>
is identical to <code>(A B) | (C D)</code>.</p>
</dd>
<dt class="label">A | B</dt>
<dd>
<p>matches <code>A</code> or <code>B</code> but not both.</p>
</dd>
<dt class="label">A - B</dt>
<dd>
<p>matches any string that matches <code>A</code> but does not
match <code>B</code>.</p>
</dd>
<dt class="label">A+</dt>
<dd>
<p>matches one or more occurrences of <code>A</code>. Concatenation
has higher precedence than alternation; thus <code>A+ | B+</code>
is identical to <code>(A+) | (B+)</code>.</p>
</dd>
</dl>
<dl>
<dt class="label">A*</dt>
<dd>
<p>matches zero or more occurrences of <code>A</code>.
Concatenation has higher precedence than alternation; thus <code>A*
| B*</code> is identical to <code>(A*) | (B*)</code></p>
</dd>
</dl>
</div>
<div class="div3">
<h4><a name="extra-grammatical-constraints" id=
"extra-grammatical-constraints"></a>A.1.2 Extra-grammatical
Constraints</h4>
<p>This section contains constraints on the EBNF productions, which
are required to parse legal sentences. The notes below are
referenced from the right side of the production, with the
notation: <em>/* xgc: &lt;id&gt; */</em>.</p>
<div class="constraint">
<p class="prefix"><a name="parse-note-leading-lone-slash" id=
"parse-note-leading-lone-slash"></a><b>Constraint:
leading-lone-slash</b></p>
<p>A single slash may appear either as a complete path expression
or as the first part of a path expression in which it is followed
by a <a href="#doc-xquery-RelativePathExpr">RelativePathExpr</a>.
In some cases, the next token after the slash is insufficient to
allow a parser to distinguish these two possibilities: the
<code>*</code> token and keywords like <code>union</code> could be
either an operator or a <a href="#doc-xquery-NameTest">NameTest</a>
<span class="xquery"><span class="xquery">, and the
<code>&lt;</code> token could be either an operator or the start of
a <a href=
"#doc-xquery-DirectConstructor">DirectConstructor</a></span></span>.
For example, without lookahead the first part of the expression
<code>/ * 5</code> is easily taken to be a complete expression,
<code>/ *</code>, which has a very different interpretation (the
child nodes of <code>/</code>).</p>
<p>Therefore to reduce the need for lookahead, if the token
immediately following a slash can form the start of a <a href=
"#doc-xquery-RelativePathExpr">RelativePathExpr</a>, then the slash
must be the beginning of a <a href=
"#doc-xquery-PathExpr">PathExpr</a>, not the entirety of it.</p>
<p>A single slash may be used as the left-hand argument of an
operator by parenthesizing it: <code>(/) * 5</code>. The expression
<code>5 * /</code>, on the other hand, is legal without
parentheses.</p>
</div>
<div class="constraint">
<p class="prefix"><a name="parse-note-xml-version" id=
"parse-note-xml-version"></a><b>Constraint: xml-version</b></p>
<p>An implementation's choice to support the <a href="#XML">[XML
1.0]</a> and <a href="#XMLNAMES">[XML Names]</a>, or <a href=
"#XML1.1">[XML 1.1]</a> and <a href="#XMLNAMES11">[XML Names
1.1]</a> lexical specification determines the external document
from which to obtain the definition for this production. The EBNF
only has references to the 1.0 versions. In some cases, the XML 1.0
and XML 1.1 definitions may be exactly the same. Also please note
that these external productions follow the whitespace rules of
their respective specifications, and not the rules of this
specification, in particular <a href=
"#DefaultWhitespaceHandling"><b>A.2.4.1 Default Whitespace
Handling</b></a>. Thus <code>prefix : localname</code> is not a
valid QName for purposes of this specification, just as it is not
permitted in a XML document. Also, comments are not permissible on
either side of the colon. Also extra-grammatical constraints such
as well-formedness constraints must be taken into account.</p>
</div>
<div class="constraint">
<p class="prefix"><a name="parse-note-reserved-function-names" id=
"parse-note-reserved-function-names"></a><b>Constraint:
reserved-function-names</b></p>
<p>Unprefixed function names spelled the same way as language
keywords could make the language harder to recognize. For instance,
<code>if(foo)</code> could be taken either as a <a href=
"#doc-xquery-FunctionCall">FunctionCall</a> or as the beginning of
an <a href="#doc-xquery-IfExpr">IfExpr</a>. Therefore it is not
legal syntax for a user to invoke functions with unprefixed names
which match any of the names in <a href=
"#id-reserved-fn-names"><b>A.3 Reserved Function Names</b></a>.</p>
<p>A function named "if" can be called by binding its namespace to
a prefix and using the prefixed form: "library:if(foo)" instead of
"if(foo)".</p>
</div>
<div class="constraint">
<p class="prefix"><a name="parse-note-occurrence-indicators" id=
"parse-note-occurrence-indicators"></a><b>Constraint:
occurrence-indicators</b></p>
<p>As written, the grammar in <a href="#nt-bnf"><b>A XQuery
Grammar</b></a> is ambiguous for some forms using the '+' and '*'
Kleene operators. The ambiguity is resolved as follows: these
operators are tightly bound to the <a href=
"#doc-xquery-SequenceType">SequenceType</a> expression, and have
higher precedence than other uses of these symbols. Any occurrence
of '+' and '*', as well as '?', following a sequence type is
assumed to be an occurrence indicator. That is, a "+", "*", or "?"
immediately following an <a href=
"#doc-xquery-ItemType">ItemType</a> must be an <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a>. Thus,
<code>4 treat as item() + - 5</code> must be interpreted as
<code>(4 treat as item()+) - 5</code>, taking the '+' as an
OccurrenceIndicator and the '-' as a subtraction operator. To force
the interpretation of "+" as an addition operator (and the
corresponding interpretation of the "-" as a unary minus),
parentheses may be used: the form <code>(4 treat as item()) +
-5</code> surrounds the <a href=
"#doc-xquery-SequenceType">SequenceType</a> expression with
parentheses and leads to the desired interpretation.</p>
<p>This rule has as a consequence that certain forms which would
otherwise be legal and unambiguous are not recognized: in "4 treat
as item() + 5", the "+" is taken as an <a href=
"#doc-xquery-OccurrenceIndicator">OccurrenceIndicator</a>, and not
as an operator, which means this is not a legal expression.</p>
</div>
</div>
<div class="div3">
<h4><a name="notes-on-parsing" id="notes-on-parsing"></a>A.1.3
Grammar Notes</h4>
<p>This section contains general notes on the EBNF productions,
which may be helpful in understanding how to interpret and
implement the EBNF. These notes are not normative. The notes below
are referenced from the right side of the production, with the
notation: <em>/* gn: &lt;id&gt; */</em>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<dl>
<dt class="label"><a name="parse-note-parens" id=
"parse-note-parens"></a>grammar-note: parens</dt>
<dd>
<p>Look-ahead is required to distinguish <a href=
"#doc-xquery-FunctionCall">FunctionCall</a> from a QName or keyword
followed by a <span class="xquery"><span class="xquery"><a href=
"#doc-xquery-Pragma">Pragma</a> or</span></span> <a href=
"#doc-xquery-Comment">Comment</a>. For example: <code>address (:
this may be empty :)</code> may be mistaken for a call to a
function named "address" unless this lookahead is employed. Another
example is <code>for (: whom the bell :) $tolls in 3 return
$tolls</code>, where the keyword "for" must not be mistaken for a
function name.</p>
</dd>
<dt class="label"><a name="parse-note-comments" id=
"parse-note-comments"></a>grammar-note: comments</dt>
<dd>
<p>Comments are allowed everywhere that <a title=
"ignorable whitespace" href="#IgnorableWhitespace">ignorable
whitespace</a> is allowed, and the <a href=
"#doc-xquery-Comment">Comment</a> symbol does not explicitly appear
on the right-hand side of the grammar (except in its own
production). See <a href="#DefaultWhitespaceHandling"><b>A.2.4.1
Default Whitespace Handling</b></a>. <span class=
"xquery"><span class="xquery">Note that comments are not allowed in
direct constructor content, though they are allowed in nested
<a href=
"#doc-xquery-EnclosedExpr">EnclosedExprs</a>.</span></span></p>
<p>A comment can contain nested comments, as long as all "(:" and
":)" patterns are balanced, no matter where they occur within the
outer comment.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Lexical analysis may typically handle nested comments by
incrementing a counter for each "(:" pattern, and decrementing the
counter for each ":)" pattern. The comment does not terminate until
the counter is back to zero.</p>
</div>
<p>Some illustrative examples:</p>
<ul>
<li>
<p><code>(: commenting out a (: comment :) may be confusing, but
often helpful :)</code> is a legal Comment, since balanced nesting
of comments is allowed.</p>
</li>
<li>
<p><code>"this is just a string :)"</code> is a legal expression.
However, <code>(: "this is just a string :)" :)</code> will cause a
syntax error. Likewise, <code>"this is another string (:"</code> is
a legal expression, but <code>(: "this is another string (:"
:)</code> will cause a syntax error. It is a limitation of nested
comments that literal content can cause unbalanced nesting of
comments.</p>
</li>
<li>
<p><code>for (: set up loop :) $i in $x return $i</code> is
syntactically legal, ignoring the comment.</p>
</li>
<li>
<p><code>5 instance (: strange place for a comment :) of
xs:integer</code> is also syntactically valid.</p>
</li>
<li class="xquery">
<p><code>&lt;eg (: an example:)&gt;{$i//title}&lt;/eg&gt;</code> is
not syntactically valid.</p>
</li>
<li class="xquery">
<p><code>&lt;eg&gt; (: an example:) &lt;/eg&gt;</code> is
syntactically valid, but the characters that look like a comment
are in fact literal element content.</p>
</li>
</ul>
</dd>
</dl>
</div>
</div>
</div>
<div class="div2">
<h3><a name="lexical-structure" id="lexical-structure"></a>A.2
Lexical structure</h3>
<p>The terminal symbols assumed by the grammar above are described
in this section.</p>
<p>Quoted strings appearing in production rules are terminal
symbols.</p>
<p>Other terminal symbols are defined in <a href=
"#terminal-symbols"><b>A.2.1 Terminal Symbols</b></a>.</p>
<div class="xquery">
<p class="xquery">It is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> whether the
lexical rules of <a href="#XML">[XML 1.0]</a> and <a href=
"#XMLNAMES">[XML Names]</a> are followed, or alternatively, the
lexical rules of <a href="#XML1.1">[XML 1.1]</a> and <a href=
"#XMLNAMES11">[XML Names 1.1]</a> are followed. Implementations
that support the full <a href="#XML1.1">[XML 1.1]</a> character set
<a title="should" href="#should">SHOULD</a>, for purposes of
interoperability, provide a mode that follows only the <a href=
"#XML">[XML 1.0]</a> and <a href="#XMLNAMES">[XML Names]</a>
lexical rules.</p>
</div>
<p>When tokenizing, the longest possible match that is valid in the
current context is used.</p>
<p>All keywords are case sensitive. Keywords are not reserved—that
is, any QName may duplicate a keyword except as noted in <a href=
"#id-reserved-fn-names"><b>A.3 Reserved Function Names</b></a>.</p>
<div class="div3">
<h4><a name="terminal-symbols" id="terminal-symbols"></a>A.2.1
Terminal Symbols</h4>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-IntegerLiteral" id=
"prod-xquery-IntegerLiteral"></a>[141]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-IntegerLiteral">IntegerLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Digits">Digits</a></code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DecimalLiteral" id=
"prod-xquery-DecimalLiteral"></a>[142]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DecimalLiteral">DecimalLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>("." <a href="#prod-xquery-Digits">Digits</a>) |
(<a href="#prod-xquery-Digits">Digits</a> "." [0-9]*)</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-DoubleLiteral" id=
"prod-xquery-DoubleLiteral"></a>[143]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-DoubleLiteral">DoubleLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(("." <a href="#prod-xquery-Digits">Digits</a>) |
(<a href="#prod-xquery-Digits">Digits</a> ("." [0-9]*)?)) [eE]
[+-]? <a href="#prod-xquery-Digits">Digits</a></code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-StringLiteral" id=
"prod-xquery-StringLiteral"></a>[144]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-StringLiteral">StringLiteral</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>('"' (<a href=
"#prod-xquery-PredefinedEntityRef">PredefinedEntityRef</a> |
<a href="#prod-xquery-CharRef">CharRef</a> | <a href=
"#prod-xquery-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"') | ("'"
(<a href="#prod-xquery-PredefinedEntityRef">PredefinedEntityRef</a>
| <a href="#prod-xquery-CharRef">CharRef</a> | <a href=
"#prod-xquery-EscapeApos">EscapeApos</a> | [^'&amp;])*
"'")</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PredefinedEntityRef" id=
"prod-xquery-PredefinedEntityRef"></a>[145]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-PredefinedEntityRef">PredefinedEntityRef</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos")
";"</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-EscapeQuot" id=
"prod-xquery-EscapeQuot"></a>[146]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-EscapeQuot">EscapeQuot</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>'""'</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-EscapeApos" id=
"prod-xquery-EscapeApos"></a>[147]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-EscapeApos">EscapeApos</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"''"</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-ElementContentChar" id=
"prod-xquery-ElementContentChar"></a>[148]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-ElementContentChar">ElementContentChar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Char">Char</a> -
[{}&lt;&amp;]</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-QuotAttrContentChar" id=
"prod-xquery-QuotAttrContentChar"></a>[149]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-QuotAttrContentChar">QuotAttrContentChar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Char">Char</a> -
["{}&lt;&amp;]</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-AposAttrContentChar" id=
"prod-xquery-AposAttrContentChar"></a>[150]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-AposAttrContentChar">AposAttrContentChar</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href="#prod-xquery-Char">Char</a> -
['{}&lt;&amp;]</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Comment" id=
"prod-xquery-Comment"></a>[151]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Comment">Comment</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>"(:" (<a href=
"#prod-xquery-CommentContents">CommentContents</a> | <a href=
"#prod-xquery-Comment">Comment</a>)* ":)"</code></td>
<td><i>/* <a href="#ws-explicit">ws: explicit</a> */</i></td>
</tr>
<tr valign="baseline">
<td></td>
<td></td>
<td></td>
<td></td>
<td><i>/* <a href="#parse-note-comments">gn: comments</a>
*/</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-PITarget" id=
"prod-xquery-PITarget"></a>[152]&#160;&#160;&#160;</td>
<td><code>PITarget</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"http://www.w3.org/TR/REC-xml/#NT-PITarget">[http://www.w3.org/TR/REC-xml#NT-PITarget]</a><sup><small>XML</small></sup></code></td>
<td><i>/* <a href="#parse-note-xml-version">xgs: xml-version</a>
*/</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CharRef" id=
"prod-xquery-CharRef"></a>[153]&#160;&#160;&#160;</td>
<td><code>CharRef</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"http://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td>
<td><i>/* <a href="#parse-note-xml-version">xgs: xml-version</a>
*/</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-QName" id=
"prod-xquery-QName"></a>[154]&#160;&#160;&#160;</td>
<td><code>QName</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"http://www.w3.org/TR/REC-xml-names/#NT-QName">[http://www.w3.org/TR/REC-xml-names/#NT-QName]</a><sup><small>Names</small></sup></code></td>
<td><i>/* <a href="#parse-note-xml-version">xgs: xml-version</a>
*/</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-NCName" id=
"prod-xquery-NCName"></a>[155]&#160;&#160;&#160;</td>
<td><code>NCName</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"http://www.w3.org/TR/REC-xml-names/#NT-NCName">[http://www.w3.org/TR/REC-xml-names/#NT-NCName]</a><sup><small>Names</small></sup></code></td>
<td><i>/* <a href="#parse-note-xml-version">xgs: xml-version</a>
*/</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-S" id=
"prod-xquery-S"></a>[156]&#160;&#160;&#160;</td>
<td><code>S</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"http://www.w3.org/TR/REC-xml/#NT-S">[http://www.w3.org/TR/REC-xml#NT-S]</a><sup><small>XML</small></sup></code></td>
<td><i>/* <a href="#parse-note-xml-version">xgs: xml-version</a>
*/</i></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Char" id=
"prod-xquery-Char"></a>[157]&#160;&#160;&#160;</td>
<td><code>Char</code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code><a href=
"http://www.w3.org/TR/REC-xml/#NT-Char">[http://www.w3.org/TR/REC-xml#NT-Char]</a><sup><small>XML</small></sup></code></td>
<td><i>/* <a href="#parse-note-xml-version">xgs: xml-version</a>
*/</i></td>
</tr>
</tbody>
</table>
<p>The following symbols are used only in the definition of
terminal symbols; they are not terminal symbols in the grammar of
<a href="#id-grammar"><b>A.1 EBNF</b></a>.</p>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-Digits" id=
"prod-xquery-Digits"></a>[158]&#160;&#160;&#160;</td>
<td><code><a href="#doc-xquery-Digits">Digits</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>[0-9]+</code></td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td><a name="prod-xquery-CommentContents" id=
"prod-xquery-CommentContents"></a>[159]&#160;&#160;&#160;</td>
<td><code><a href=
"#doc-xquery-CommentContents">CommentContents</a></code></td>
<td>&#160;&#160;&#160;::=&#160;&#160;&#160;</td>
<td><code>(<a href="#prod-xquery-Char">Char</a>+ - (Char* ('(:' |
':)') Char*))</code></td>
</tr>
</tbody>
</table>
</div>
<div class="div3">
<h4><a name="id-terminal-delimitation" id=
"id-terminal-delimitation"></a>A.2.2 Terminal Delimitation</h4>
<p>XQuery 1.0 expressions consist of <a href=
"#terminal-symbols">terminal symbols</a> and <a title=
"symbol separators" href="#symbolseparators">symbol
separators</a>.</p>
<p>Terminal symbols that are not used exclusively in <a href=
"#ws-explicit">/* ws: explicit */</a> productions are of two kinds:
delimiting and non-delimiting.</p>
<p>[<a name="delimiting-token" id="delimiting-token" title=
"delimiting terminal symbol">Definition</a>: The <b>delimiting
terminal symbols</b> are: <a href="#prod-xquery-S">S</a>, "!=",
<a href="#prod-xquery-StringLiteral">StringLiteral</a>, "#)", "$",
"(", "(#", ")", "*", "+", (comma), "-", "--&gt;", (dot), "..", "/",
"//", "/&gt;", (colon), "::", ":=", (semi-colon), "&lt;",
"&lt;!--", "&lt;![CDATA[", "&lt;/", "&lt;&lt;", "&lt;=", "&lt;?",
"=", "&gt;", "&gt;=", "&gt;&gt;", "?", "?&gt;", "@", "[", "]",
"]]&gt;", "{", "|", "}"]</p>
<p>[<a name="non-delimiting-token" id="non-delimiting-token" title=
"non-delimiting terminal symbol">Definition</a>: The
<b>non-delimiting terminal symbols</b> are: <a href=
"#prod-xquery-IntegerLiteral">IntegerLiteral</a>, <a href=
"#prod-xquery-NCName">NCName</a>, <a href=
"#prod-xquery-DecimalLiteral">DecimalLiteral</a>, <a href=
"#prod-xquery-DoubleLiteral">DoubleLiteral</a>, <a href=
"#prod-xquery-QName">QName</a>, "ancestor", "ancestor-or-self",
"and", "as", "ascending", "at", "attribute", "base-uri",
"boundary-space", "by", "case", "cast", "castable", "child",
"collation", "comment", "construction", "copy-namespaces",
"declare", "default", "descendant", "descendant-or-self",
"descending", "div", "document", "document-node", "element",
"else", "empty", "empty-sequence", "encoding", "eq", "every",
"except", "external", "following", "following-sibling", "for",
"function", "ge", "greatest", "gt", "idiv", "if", "import", "in",
"inherit", "instance", "intersect", "is", "item", "lax", "le",
"least", "let", "lt", "mod", "module", "namespace", "ne",
"no-inherit", "no-preserve", "node", "of", "option", "or", "order",
"ordered", "ordering", "parent", "preceding", "preceding-sibling",
"preserve", "processing-instruction", "return", "satisfies",
"schema", "schema-attribute", "schema-element", "self", "some",
"stable", "strict", "strip", "text", "then", "to", "treat",
"typeswitch", "union", "unordered", "validate", "variable",
"version", "where", "xquery"]</p>
<p>[<a name="symbolseparators" id="symbolseparators" title=
"symbol separators">Definition</a>: <a title="whitespace" href=
"#Whitespace">Whitespace</a> and <a href=
"#doc-xquery-Comment">Comments</a> function as <b>symbol
separators</b>. For the most part, they are not mentioned in the
grammar, and may occur between any two terminal symbols mentioned
in the grammar, except where that is forbidden by the <a href=
"#ws-explicit">/* ws: explicit */</a> annotation in the EBNF, or by
the <a href="#parse-note-xml-version">/* xgs: xml-version */</a>
annotation. ]</p>
<p>It is customary to separate consecutive terminal symbols by
<a title="whitespace" href="#Whitespace">whitespace</a> and
<a href="#doc-xquery-Comment">Comments</a>, but this is required
only when otherwise two non-delimiting symbols would be adjacent to
each other. There are two exceptions to this, that of "." and "-",
which do require a <a title="symbol separators" href=
"#symbolseparators">symbol separator</a> if they follow a QName or
NCName. Also, "." requires a separator if it precedes or follows a
numeric literal.</p>
</div>
<div class="div3">
<h4><a name="id-eol-handling" id="id-eol-handling"></a>A.2.3
End-of-Line Handling</h4>
<p>The XQuery processor must behave as if it normalized all line
breaks on input, before parsing. The normalization should be done
according to the choice to support either <a href="#XML">[XML
1.0]</a> or <a href="#XML1.1">[XML 1.1]</a> lexical processing.</p>
<div class="div4">
<h5><a name="id-xml10-eol-handling" id=
"id-xml10-eol-handling"></a>A.2.3.1 XML 1.0 End-of-Line
Handling</h5>
<p>For <a href="#XML">[XML 1.0]</a> processing, all of the
following must be translated to a single #xA character:</p>
<ol class="enumar">
<li>
<p>the two-character sequence #xD #xA</p>
</li>
<li>
<p>any #xD character that is not immediately followed by #xA.</p>
</li>
</ol>
</div>
<div class="div4">
<h5><a name="id-xml11-eol-handling" id=
"id-xml11-eol-handling"></a>A.2.3.2 XML 1.1 End-of-Line
Handling</h5>
<p>For <a href="#XML1.1">[XML 1.1]</a> processing, all of the
following must be translated to a single #xA character:</p>
<ol class="enumar">
<li>
<p>the two-character sequence #xD #xA</p>
</li>
<li>
<p>the two-character sequence #xD #x85</p>
</li>
<li>
<p>the single character #x85</p>
</li>
<li>
<p>the single character #x2028</p>
</li>
<li>
<p>any #xD character that is not immediately followed by #xA or
#x85.</p>
</li>
</ol>
<div class="xquery">
<p class="xquery">The characters #x85 and #x2028 cannot be reliably
recognized and translated until the <a href=
"#doc-xquery-VersionDecl">VersionDecl</a> declaration (if present)
has been read.</p>
</div>
</div>
</div>
<div class="div3">
<h4><a name="whitespace-rules" id="whitespace-rules"></a>A.2.4
Whitespace Rules</h4>
<div class="div4">
<h5><a name="DefaultWhitespaceHandling" id=
"DefaultWhitespaceHandling"></a>A.2.4.1 Default Whitespace
Handling</h5>
<p>[<a name="Whitespace" id="Whitespace" title=
"whitespace">Definition</a>: A <b>whitespace</b> character is any
of the characters defined by <a href=
"http://www.w3.org/TR/REC-xml/#NT-S">[http://www.w3.org/TR/REC-xml/#NT-S]</a>.]</p>
<p>[<a name="IgnorableWhitespace" id="IgnorableWhitespace" title=
"ignorable whitespace">Definition</a>: <b>Ignorable whitespace</b>
consists of any <a title="whitespace" href=
"#Whitespace">whitespace</a> characters that may occur between
<a title="terminal" href="#terminal">terminals</a>, unless these
characters occur in the context of a production marked with a
<a href="#ExplicitWhitespaceHandling">ws:explicit</a> annotation,
in which case they can occur only where explicitly specified (see
<a href="#ExplicitWhitespaceHandling"><b>A.2.4.2 Explicit
Whitespace Handling</b></a>).] Ignorable whitespace characters are
not significant to the semantics of an expression. Whitespace is
allowed before the first terminal and after the last terminal of a
module. Whitespace is allowed between any two <a title="terminal"
href="#terminal">terminals</a>. <a href=
"#doc-xquery-Comment">Comments</a> may also act as "whitespace" to
prevent two adjacent terminals from being recognized as one. Some
illustrative examples are as follows:</p>
<ul>
<li>
<p><code>foo- foo</code> results in a syntax error. "foo-" would be
recognized as a QName.</p>
</li>
<li>
<p><code>foo -foo</code> is syntactically equivalent to <code>foo -
foo</code>, two QNames separated by a subtraction operator.</p>
</li>
<li>
<p><code>foo(: This is a comment :)- foo</code> is syntactically
equivalent to <code>foo - foo</code>. This is because the comment
prevents the two adjacent terminals from being recognized as
one.</p>
</li>
<li>
<p><code>foo-foo</code> is syntactically equivalent to single
QName. This is because "-" is a valid character in a QName. When
used as an operator after the characters of a name, the "-" must be
separated from the name, e.g. by using whitespace or
parentheses.</p>
</li>
<li>
<p><code>10div 3</code> results in a syntax error.</p>
</li>
<li>
<p><code>10 div3</code> also results in a syntax error.</p>
</li>
<li>
<p><code>10div3</code> also results in a syntax error.</p>
</li>
</ul>
</div>
<div class="div4">
<h5><a name="ExplicitWhitespaceHandling" id=
"ExplicitWhitespaceHandling"></a>A.2.4.2 Explicit Whitespace
Handling</h5>
<p>Explicit whitespace notation is specified with the EBNF
productions, when it is different from the default rules, using the
notation shown below. This notation is not inherited. In other
words, if an EBNF rule is marked as /* ws: explicit */, the
notation does not automatically apply to all the 'child' EBNF
productions of that rule.</p>
<dl>
<dt class="label"><a name="ws-explicit" id="ws-explicit"></a>ws:
explicit</dt>
<dd>
<p>/* ws: explicit */ means that the EBNF notation explicitly
notates, with <code>S</code> or otherwise, where <a title=
"whitespace" href="#Whitespace">whitespace characters</a> are
allowed. In productions with the /* ws: explicit */ annotation,
<a href="#DefaultWhitespaceHandling"><b>A.2.4.1 Default Whitespace
Handling</b></a> does not apply. <a href=
"#doc-xquery-Comment">Comments</a> are also not allowed in these
productions.</p>
</dd>
</dl>
<div class="xquery">
<p id="ws-explicit-lex-states" class="xquery">For example,
whitespace is not freely allowed by the direct constructor
productions, but is specified explicitly in the grammar, in order
to be more consistent with XML.</p>
</div>
</div>
</div>
</div>
<div class="div2">
<h3><a name="id-reserved-fn-names" id=
"id-reserved-fn-names"></a>A.3 Reserved Function Names</h3>
<p>The following names are not allowed as function names in an
unprefixed form because expression syntax takes precedence.</p>
<ul>
<li>
<p><code>attribute</code></p>
</li>
<li>
<p><code>comment</code></p>
</li>
<li>
<p><code>document-node</code></p>
</li>
<li>
<p><code>element</code></p>
</li>
<li>
<p><code>empty-sequence</code></p>
</li>
<li>
<p><code>if</code></p>
</li>
<li>
<p><code>item</code></p>
</li>
<li>
<p><code>node</code></p>
</li>
<li>
<p><code>processing-instruction</code></p>
</li>
<li>
<p><code>schema-attribute</code></p>
</li>
<li>
<p><code>schema-element</code></p>
</li>
<li>
<p><code>text</code></p>
</li>
<li>
<p><code>typeswitch</code></p>
</li>
</ul>
</div>
<div class="div2">
<h3><a name="id-precedence-order" id="id-precedence-order"></a>A.4
Precedence Order</h3>
<p>The grammar in <a href="#id-grammar"><b>A.1 EBNF</b></a>
normatively defines built-in precedence among the operators of
XQuery. These operators are summarized here to make clear the order
of their precedence from lowest to highest. The associativity
column indicates the order in which operators of equal precedence
in an expression are applied.</p>
<table border="1">
<tbody>
<tr>
<th>#</th>
<th>Operator</th>
<th>Associativity</th>
</tr>
<tr>
<td>1</td>
<td>, (comma)</td>
<td>left-to-right</td>
</tr>
<tr class="xquery">
<td>2</td>
<td>:= (assignment)</td>
<td>right-to-left</td>
</tr>
<tr>
<td>3</td>
<td><span class="xquery"><span class="xquery"><a href=
"#doc-xquery-FLWORExpr">for</a>,</span></span> <a href=
"#doc-xquery-QuantifiedExpr">some, every</a>, <span class=
"xquery"><span class="xquery"><a href=
"#doc-xquery-TypeswitchExpr">typeswitch</a>,</span></span> <a href=
"#doc-xquery-IfExpr">if</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>4</td>
<td><a href="#doc-xquery-OrExpr">or</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>5</td>
<td><a href="#doc-xquery-AndExpr">and</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>6</td>
<td><a href="#doc-xquery-ValueComp">eq, ne, lt, le, gt, ge</a>,
<a href="#doc-xquery-GeneralComp">=, !=, &lt;, &lt;=, &gt;,
&gt;=</a>, <a href="#doc-xquery-NodeComp">is</a>, <a href=
"#doc-xquery-NodeComp">&lt;&lt;, &gt;&gt;</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>7</td>
<td><a href="#doc-xquery-RangeExpr">to</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>8</td>
<td><a href="#doc-xquery-AdditiveExpr">+, -</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>9</td>
<td><a href="#doc-xquery-MultiplicativeExpr">*, div, idiv,
mod</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>10</td>
<td><a href="#doc-xquery-UnionExpr">union, |</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>11</td>
<td><a href="#doc-xquery-IntersectExceptExpr">intersect,
except</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>12</td>
<td><a href="#doc-xquery-InstanceofExpr">instance of</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>13</td>
<td><a href="#doc-xquery-TreatExpr">treat</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>14</td>
<td><a href="#doc-xquery-CastableExpr">castable</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>15</td>
<td><a href="#doc-xquery-CastExpr">cast</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>16</td>
<td><a href="#doc-xquery-UnaryExpr">-(unary), +(unary)</a></td>
<td>right-to-left</td>
</tr>
<tr>
<td>17</td>
<td><a href="#doc-xquery-OccurrenceIndicator">?,
*(OccurrenceIndicator), +(OccurrenceIndicator)</a></td>
<td>left-to-right</td>
</tr>
<tr>
<td>18</td>
<td><a href="#doc-xquery-PathExpr">/, //</a></td>
<td>left-to-right</td>
</tr>
<tr class="diff-chg" title="XQ.E26 and XP.E18">
<td>19</td>
<td><a href="#doc-xquery-Predicate">[ ]</a></td>
<td>left-to-right</td>
</tr>
</tbody>
</table>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Parentheses can be used to override the operator precedence in
the usual way. Square brackets in an expression such as A[B] serve
two roles: they act as an operator causing B to be evaluated once
for each item in the value of A, and they act as parentheses
enclosing the expression B.</p>
<div class="xquery">
<p class="xquery">Curly braces in an expression such as validate{E}
or ordered{E} perform a similar bracketing role to the parentheses
in a function call, but with the difference in most cases that E is
an Expr rather than ExprSingle, meaning that it can use the comma
operator.</p>
</div>
</div>
</div>
</div>
<div class="div1">
<h2><a name="id-type-promotion-and-operator-mapping" id=
"id-type-promotion-and-operator-mapping"></a>B Type Promotion and
Operator Mapping</h2>
<div class="div2">
<h3><a name="promotion" id="promotion"></a>B.1 Type Promotion</h3>
<p>[<a name="dt-type-promotion" id="dt-type-promotion" title=
"type promotion">Definition</a>: Under certain circumstances, an
atomic value can be promoted from one type to another. <b>Type
promotion</b> is used in evaluating function calls (see <a href=
"#id-function-calls"><b>3.1.5 Function Calls</b></a>)<span class=
"xquery"><span class="xquery">, <code>order by</code> clauses (see
<a href="#id-orderby-return"><b>3.8.3 Order By and Return
Clauses</b></a>),</span></span> and operators that accept numeric
or string operands (see <a href="#mapping"><b>B.2 Operator
Mapping</b></a>).] The following type promotions are permitted:</p>
<ol class="enumar">
<li>
<p>Numeric type promotion:</p>
<ol class="enumla">
<li>
<p>A value of type <code>xs:float</code> (or any type derived by
restriction from <code>xs:float</code>) can be promoted to the type
<code>xs:double</code>. The result is the <code>xs:double</code>
value that is the same as the original value.</p>
</li>
<li>
<p>A value of type <code>xs:decimal</code> (or any type derived by
restriction from <code>xs:decimal</code>) can be promoted to either
of the types <code>xs:float</code> or <code>xs:double</code>. The
result of this promotion is created by casting the original value
to the required type. This kind of promotion may cause loss of
precision.</p>
</li>
</ol>
</li>
<li>
<p>URI type promotion: A value of type <code>xs:anyURI</code> (or
any type derived by restriction from <code>xs:anyURI</code>) can be
promoted to the type <code>xs:string</code>. The result of this
promotion is created by casting the original value to the type
<code>xs:string</code>.</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Since <code>xs:anyURI</code> values can be promoted to
<code>xs:string</code>, functions and operators that compare
strings using the <a title="default collation" href=
"#dt-def-collation">default collation</a> also compare
<code>xs:anyURI</code> values using the <a title=
"default collation" href="#dt-def-collation">default collation</a>.
This ensures that orderings that include strings,
<code>xs:anyURI</code> values, or any combination of the two types
are consistent and well-defined.</p>
</div>
</li>
</ol>
<p>Note that <a title="type promotion" href=
"#dt-type-promotion">type promotion</a> is different from <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a>. For example:</p>
<ul>
<li>
<p>A function that expects a parameter <code>$p</code> of type
<code>xs:float</code> can be invoked with a value of type
<code>xs:decimal</code>. This is an example of <a title=
"type promotion" href="#dt-type-promotion">type promotion</a>. The
value is actually converted to the expected type. Within the body
of the function, <code>$p instance of xs:decimal</code> returns
<code>false</code>.</p>
</li>
<li>
<p>A function that expects a parameter <code>$p</code> of type
<code>xs:decimal</code> can be invoked with a value of type
<code>xs:integer</code>. This is an example of <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a>. The value retains its original type. Within the
body of the function, <code>$p instance of xs:integer</code>
returns <code>true</code>.</p>
</li>
</ul>
</div>
<div class="div2">
<h3><a name="mapping" id="mapping"></a>B.2 Operator Mapping</h3>
<p>The operator mapping tables in this section list the
combinations of types for which the various operators of XQuery are
defined. [<a name="dt-operator-function" id="dt-operator-function"
title="operator function">Definition</a>: For each operator and
valid combination of operand types, the operator mapping tables
specify a result type and an <b>operator function</b> that
implements the semantics of the operator for the given types.] The
definitions of the operator functions are given in <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>. The result of an operator may be
the raising of an error by its operator function, as defined in
<a href="#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0
Functions and Operators (Second Edition)]</a>. In some cases, the
operator function does not implement the full semantics of a given
operator. For the definition of each operator (including its
behavior for empty sequences or sequences of length greater than
one), see the descriptive material in the main part of this
document.</p>
<p>The <code>and</code> and <code>or</code> operators are defined
directly in the main body of this document, and do not occur in the
operator mapping tables.</p>
<p>If an operator in the operator mapping tables expects an operand
of type <em>ET</em>, that operator can be applied to an operand of
type <em>AT</em> if type <em>AT</em> can be converted to type
<em>ET</em> by a combination of <a title="type promotion" href=
"#dt-type-promotion">type promotion</a> and <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a>. For example, a table entry indicates that the
<code>gt</code> operator may be applied to two <code>xs:date</code>
operands, returning <code>xs:boolean</code>. Therefore, the
<code>gt</code> operator may also be applied to two (possibly
different) subtypes of <code>xs:date</code>, also returning
<code>xs:boolean</code>.</p>
<p>[<a name="dt-numeric" id="dt-numeric" title=
"numeric">Definition</a>: When referring to a type, the term
<b>numeric</b> denotes the types <code>xs:integer</code>,
<code>xs:decimal</code>, <code>xs:float</code>, and
<code>xs:double</code>.] An operator whose operands and result are
designated as <a title="numeric" href="#dt-numeric">numeric</a>
might be thought of as representing four operators, one for each of
the numeric types. For example, the numeric <code>+</code> operator
might be thought of as representing the following four
operators:</p>
<table width="80%" border="1" summary="Operators">
<tbody>
<tr>
<td align="center">Operator</td>
<td align="center">First operand type</td>
<td align="center">Second operand type</td>
<td align="center">Result type</td>
</tr>
<tr>
<td align="center"><code>+</code></td>
<td align="center"><code>xs:integer</code></td>
<td align="center"><code>xs:integer</code></td>
<td align="center"><code>xs:integer</code></td>
</tr>
<tr>
<td align="center"><code>+</code></td>
<td align="center"><code>xs:decimal</code></td>
<td align="center"><code>xs:decimal</code></td>
<td align="center"><code>xs:decimal</code></td>
</tr>
<tr>
<td align="center"><code>+</code></td>
<td align="center"><code>xs:float</code></td>
<td align="center"><code>xs:float</code></td>
<td align="center"><code>xs:float</code></td>
</tr>
<tr>
<td align="center"><code>+</code></td>
<td align="center"><code>xs:double</code></td>
<td align="center"><code>xs:double</code></td>
<td align="center"><code>xs:double</code></td>
</tr>
</tbody>
</table>
<p>A numeric operator may be validly applied to an operand of type
<em>AT</em> if type <em>AT</em> can be converted to any of the four
numeric types by a combination of <a title="type promotion" href=
"#dt-type-promotion">type promotion</a> and <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a>. If the result type of an operator is listed as
numeric, it means "the first type in the ordered list
<code>(xs:integer, xs:decimal, xs:float, xs:double)</code> into
which all operands can be converted by <a title=
"subtype substitution" href="#dt-subtype-substitution">subtype
substitution</a> and <a title="type promotion" href=
"#dt-type-promotion">type promotion</a>." As an example, suppose
that the type <code>hatsize</code> is derived from
<code>xs:integer</code> and the type <code>shoesize</code> is
derived from <code>xs:float</code>. Then if the <code>+</code>
operator is invoked with operands of type <code>hatsize</code> and
<code>shoesize</code>, it returns a result of type
<code>xs:float</code>. Similarly, if <code>+</code> is invoked with
two operands of type <code>hatsize</code> it returns a result of
type <code>xs:integer</code>.</p>
<p>[<a name="dt-gregorian" id="dt-gregorian" title=
"Gregorian">Definition</a>: In the operator mapping tables, the
term <b>Gregorian</b> refers to the types
<code>xs:gYearMonth</code>, <code>xs:gYear</code>,
<code>xs:gMonthDay</code>, <code>xs:gDay</code>, and
<code>xs:gMonth</code>.] For binary operators that accept two
Gregorian-type operands, both operands must have the same type (for
example, if one operand is of type <code>xs:gDay</code>, the other
operand must be of type <code>xs:gDay</code>.)</p>
<div class="small">
<table border="1" summary="Binary operators" class="small">
<caption>Binary Operators</caption>
<tbody>
<tr>
<th>Operator</th>
<th>Type(A)</th>
<th>Type(B)</th>
<th>Function</th>
<th>Result type</th>
</tr>
<tr>
<td>A + B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-add(A, B)</td>
<td>numeric</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:date</td>
<td>xs:yearMonthDuration</td>
<td>op:add-yearMonthDuration-to-date(A, B)</td>
<td>xs:date</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:yearMonthDuration</td>
<td>xs:date</td>
<td>op:add-yearMonthDuration-to-date(B, A)</td>
<td>xs:date</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:date</td>
<td>xs:dayTimeDuration</td>
<td>op:add-dayTimeDuration-to-date(A, B)</td>
<td>xs:date</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:dayTimeDuration</td>
<td>xs:date</td>
<td>op:add-dayTimeDuration-to-date(B, A)</td>
<td>xs:date</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:time</td>
<td>xs:dayTimeDuration</td>
<td>op:add-dayTimeDuration-to-time(A, B)</td>
<td>xs:time</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:dayTimeDuration</td>
<td>xs:time</td>
<td>op:add-dayTimeDuration-to-time(B, A)</td>
<td>xs:time</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:dateTime</td>
<td>xs:yearMonthDuration</td>
<td>op:add-yearMonthDuration-to-dateTime(A, B)</td>
<td>xs:dateTime</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:yearMonthDuration</td>
<td>xs:dateTime</td>
<td>op:add-yearMonthDuration-to-dateTime(B, A)</td>
<td>xs:dateTime</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:dateTime</td>
<td>xs:dayTimeDuration</td>
<td>op:add-dayTimeDuration-to-dateTime(A, B)</td>
<td>xs:dateTime</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dateTime</td>
<td>op:add-dayTimeDuration-to-dateTime(B, A)</td>
<td>xs:dateTime</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>op:add-yearMonthDurations(A, B)</td>
<td>xs:yearMonthDuration</td>
</tr>
<tr>
<td>A + B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>op:add-dayTimeDurations(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A - B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-subtract(A, B)</td>
<td>numeric</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>op:subtract-dates(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:date</td>
<td>xs:yearMonthDuration</td>
<td>op:subtract-yearMonthDuration-from-date(A, B)</td>
<td>xs:date</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:date</td>
<td>xs:dayTimeDuration</td>
<td>op:subtract-dayTimeDuration-from-date(A, B)</td>
<td>xs:date</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>op:subtract-times(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:time</td>
<td>xs:dayTimeDuration</td>
<td>op:subtract-dayTimeDuration-from-time(A, B)</td>
<td>xs:time</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>op:subtract-dateTimes(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:dateTime</td>
<td>xs:yearMonthDuration</td>
<td>op:subtract-yearMonthDuration-from-dateTime(A, B)</td>
<td>xs:dateTime</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:dateTime</td>
<td>xs:dayTimeDuration</td>
<td>op:subtract-dayTimeDuration-from-dateTime(A, B)</td>
<td>xs:dateTime</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>op:subtract-yearMonthDurations(A, B)</td>
<td>xs:yearMonthDuration</td>
</tr>
<tr>
<td>A - B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>op:subtract-dayTimeDurations(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A * B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-multiply(A, B)</td>
<td>numeric</td>
</tr>
<tr>
<td>A * B</td>
<td>xs:yearMonthDuration</td>
<td>numeric</td>
<td>op:multiply-yearMonthDuration(A, B)</td>
<td>xs:yearMonthDuration</td>
</tr>
<tr>
<td>A * B</td>
<td>numeric</td>
<td>xs:yearMonthDuration</td>
<td>op:multiply-yearMonthDuration(B, A)</td>
<td>xs:yearMonthDuration</td>
</tr>
<tr>
<td>A * B</td>
<td>xs:dayTimeDuration</td>
<td>numeric</td>
<td>op:multiply-dayTimeDuration(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A * B</td>
<td>numeric</td>
<td>xs:dayTimeDuration</td>
<td>op:multiply-dayTimeDuration(B, A)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A idiv B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-integer-divide(A, B)</td>
<td>xs:integer</td>
</tr>
<tr>
<td>A div B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-divide(A, B)</td>
<td>numeric; but xs:decimal if both operands are xs:integer</td>
</tr>
<tr>
<td>A div B</td>
<td>xs:yearMonthDuration</td>
<td>numeric</td>
<td>op:divide-yearMonthDuration(A, B)</td>
<td>xs:yearMonthDuration</td>
</tr>
<tr>
<td>A div B</td>
<td>xs:dayTimeDuration</td>
<td>numeric</td>
<td>op:divide-dayTimeDuration(A, B)</td>
<td>xs:dayTimeDuration</td>
</tr>
<tr>
<td>A div B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>op:divide-yearMonthDuration-by-yearMonthDuration (A, B)</td>
<td>xs:decimal</td>
</tr>
<tr>
<td>A div B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>op:divide-dayTimeDuration-by-dayTimeDuration (A, B)</td>
<td>xs:decimal</td>
</tr>
<tr>
<td>A mod B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-mod(A, B)</td>
<td>numeric</td>
</tr>
<tr>
<td>A eq B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:boolean</td>
<td>xs:boolean</td>
<td>op:boolean-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:string</td>
<td>xs:string</td>
<td>op:numeric-equal(fn:compare(A, B), 0)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>op:date-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>op:time-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>op:dateTime-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:duration</td>
<td>xs:duration</td>
<td>op:duration-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>Gregorian</td>
<td>Gregorian</td>
<td>op:gYear-equal(A, B) etc.</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:hexBinary</td>
<td>xs:hexBinary</td>
<td>op:hex-binary-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:base64Binary</td>
<td>xs:base64Binary</td>
<td>op:base64-binary-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:anyURI</td>
<td>xs:anyURI</td>
<td>op:numeric-equal(fn:compare(A, B), 0)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:QName</td>
<td>xs:QName</td>
<td>op:QName-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A eq B</td>
<td>xs:NOTATION</td>
<td>xs:NOTATION</td>
<td>op:NOTATION-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>numeric</td>
<td>numeric</td>
<td>fn:not(op:numeric-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:boolean</td>
<td>xs:boolean</td>
<td>fn:not(op:boolean-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:string</td>
<td>xs:string</td>
<td>fn:not(op:numeric-equal(fn:compare(A, B), 0))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>fn:not(op:date-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>fn:not(op:time-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>fn:not(op:dateTime-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:duration</td>
<td>xs:duration</td>
<td>fn:not(op:duration-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>Gregorian</td>
<td>Gregorian</td>
<td>fn:not(op:gYear-equal(A, B)) etc.</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:hexBinary</td>
<td>xs:hexBinary</td>
<td>fn:not(op:hex-binary-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:base64Binary</td>
<td>xs:base64Binary</td>
<td>fn:not(op:base64-binary-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:anyURI</td>
<td>xs:anyURI</td>
<td>fn:not(op:numeric-equal(fn:compare(A, B), 0))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:QName</td>
<td>xs:QName</td>
<td>fn:not(op:QName-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ne B</td>
<td>xs:NOTATION</td>
<td>xs:NOTATION</td>
<td>fn:not(op:NOTATION-equal(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:boolean</td>
<td>xs:boolean</td>
<td>op:boolean-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:string</td>
<td>xs:string</td>
<td>op:numeric-greater-than(fn:compare(A, B), 0)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>op:date-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>op:time-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>op:dateTime-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>op:yearMonthDuration-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>op:dayTimeDuration-greater-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A gt B</td>
<td>xs:anyURI</td>
<td>xs:anyURI</td>
<td>op:numeric-greater-than(fn:compare(A, B), 0)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:boolean</td>
<td>xs:boolean</td>
<td>op:boolean-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:string</td>
<td>xs:string</td>
<td>op:numeric-less-than(fn:compare(A, B), 0)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>op:date-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>op:time-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>op:dateTime-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>op:yearMonthDuration-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>op:dayTimeDuration-less-than(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A lt B</td>
<td>xs:anyURI</td>
<td>xs:anyURI</td>
<td>op:numeric-less-than(fn:compare(A, B), 0)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-greater-than(A, B) or op:numeric-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:boolean</td>
<td>xs:boolean</td>
<td>fn:not(op:boolean-less-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:string</td>
<td>xs:string</td>
<td>op:numeric-greater-than(fn:compare(A, B), -1)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>fn:not(op:date-less-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>fn:not(op:time-less-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>fn:not(op:dateTime-less-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>fn:not(op:yearMonthDuration-less-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>fn:not(op:dayTimeDuration-less-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A ge B</td>
<td>xs:anyURI</td>
<td>xs:anyURI</td>
<td>op:numeric-greater-than(fn:compare(A, B), -1)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>numeric</td>
<td>numeric</td>
<td>op:numeric-less-than(A, B) or op:numeric-equal(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:boolean</td>
<td>xs:boolean</td>
<td>fn:not(op:boolean-greater-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:string</td>
<td>xs:string</td>
<td>op:numeric-less-than(fn:compare(A, B), 1)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:date</td>
<td>xs:date</td>
<td>fn:not(op:date-greater-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:time</td>
<td>xs:time</td>
<td>fn:not(op:time-greater-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:dateTime</td>
<td>xs:dateTime</td>
<td>fn:not(op:dateTime-greater-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:yearMonthDuration</td>
<td>xs:yearMonthDuration</td>
<td>fn:not(op:yearMonthDuration-greater-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:dayTimeDuration</td>
<td>xs:dayTimeDuration</td>
<td>fn:not(op:dayTimeDuration-greater-than(A, B))</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A le B</td>
<td>xs:anyURI</td>
<td>xs:anyURI</td>
<td>op:numeric-less-than(fn:compare(A, B), 1)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A is B</td>
<td>node()</td>
<td>node()</td>
<td>op:is-same-node(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A &lt;&lt; B</td>
<td>node()</td>
<td>node()</td>
<td>op:node-before(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A &gt;&gt; B</td>
<td>node()</td>
<td>node()</td>
<td>op:node-after(A, B)</td>
<td>xs:boolean</td>
</tr>
<tr>
<td>A union B</td>
<td>node()*</td>
<td>node()*</td>
<td>op:union(A, B)</td>
<td>node()*</td>
</tr>
<tr>
<td>A | B</td>
<td>node()*</td>
<td>node()*</td>
<td>op:union(A, B)</td>
<td>node()*</td>
</tr>
<tr>
<td>A intersect B</td>
<td>node()*</td>
<td>node()*</td>
<td>op:intersect(A, B)</td>
<td>node()*</td>
</tr>
<tr>
<td>A except B</td>
<td>node()*</td>
<td>node()*</td>
<td>op:except(A, B)</td>
<td>node()*</td>
</tr>
<tr>
<td>A to B</td>
<td>xs:integer</td>
<td>xs:integer</td>
<td>op:to(A, B)</td>
<td>xs:integer*</td>
</tr>
<tr>
<td>A , B</td>
<td>item()*</td>
<td>item()*</td>
<td>op:concatenate(A, B)</td>
<td>item()*</td>
</tr>
</tbody>
</table>
</div>
<div class="small">
<table border="1" summary="Unary operators" class="small">
<caption>Unary Operators</caption>
<tbody>
<tr>
<th>Operator</th>
<th>Operand type</th>
<th>Function</th>
<th>Result type</th>
</tr>
<tr>
<td>+ A</td>
<td>numeric</td>
<td>op:numeric-unary-plus(A)</td>
<td>numeric</td>
</tr>
<tr>
<td>- A</td>
<td>numeric</td>
<td>op:numeric-unary-minus(A)</td>
<td>numeric</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="xquery">
<div class="div1">
<h2><a name="id-xq-context-components" id=
"id-xq-context-components"></a>C Context Components</h2>
<p>The tables in this section describe how values are assigned to
the various components of the static context and dynamic context,
and to the parameters that control the serialization process.</p>
<div class="div2">
<h3><a name="id-xq-static-context-components" id=
"id-xq-static-context-components"></a>C.1 Static Context
Components</h3>
<p>The following table describes the components of the <b>static
context</b>. The following aspects of each component are
described:</p>
<ul>
<li>
<p><em>Default initial value:</em> This is the initial value of the
component if it is not overridden or augmented by the
implementation or by a query.</p>
</li>
<li>
<p><em>Can be overwritten or augmented by implementation:</em>
Indicates whether an XQuery implementation is allowed to replace
the default initial value of the component by a different,
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> value
and/or to augment the default initial value by additional <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> values.</p>
</li>
<li>
<p><em>Can be overwritten or augmented by a query:</em> Indicates
whether a query is allowed to replace and/or augment the initial
value provided by default or by the implementation. If so,
indicates how this is accomplished (for example, by a declaration
in the prolog).</p>
</li>
<li>
<p><em>Scope:</em> Indicates where the component is applicable.
"Global" indicates that the component applies globally, throughout
all the modules used in a query. "Module" indicates that the
component applies throughout a <a title="module" href=
"#dt-module">module</a>. "Lexical" indicates that the component
applies within the expression in which it is defined (equivalent to
"module" if the component is declared in a <a title="Prolog" href=
"#dt-prolog">Prolog</a>.)</p>
</li>
<li>
<p><em>Consistency Rules:</em> Indicates rules that must be
observed in assigning values to the component. Additional
consistency rules may be found in <a href=
"#id-consistency-constraints"><b>2.2.5 Consistency
Constraints</b></a>.</p>
</li>
</ul>
<div class="small">
<table width="100%" border="1" summary="Static Context" class=
"small">
<caption>Static Context Components</caption>
<tbody>
<tr>
<th>Component</th>
<th>Default initial value</th>
<th>Can be overwritten or augmented by implementation?</th>
<th>Can be overwritten or augmented by a query?</th>
<th>Scope</th>
<th>Consistency rules</th>
</tr>
<tr>
<td>XPath 1.0 Compatibility Mode</td>
<td><code>false</code></td>
<td>no</td>
<td>no</td>
<td>global</td>
<td>Must be <code>false</code>.</td>
</tr>
<tr>
<td>Statically known namespaces</td>
<td><code>fn</code>, <code>xml</code>, <code>xs</code>,
<code>xsi</code>, <code>local</code></td>
<td>overwriteable and augmentable (except for
<code>xml</code>)</td>
<td>overwriteable and augmentable by prolog or element
constructor</td>
<td>lexical</td>
<td>Only one namespace can be assigned to a given prefix per
lexical scope.</td>
</tr>
<tr>
<td>Default element/type namespace</td>
<td>no namespace</td>
<td>overwriteable</td>
<td>overwriteable by prolog or element constructor</td>
<td>lexical</td>
<td>Only one default namespace per lexical scope.</td>
</tr>
<tr>
<td>Default function namespace</td>
<td><code>fn</code></td>
<td>overwriteable (not recommended)</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>None.</td>
</tr>
<tr>
<td>In-scope schema types</td>
<td>built-in types in <code>xs</code></td>
<td>augmentable</td>
<td>augmentable by schema import in prolog</td>
<td>module</td>
<td>Only one definition per global or local type.</td>
</tr>
<tr>
<td>In-scope element declarations</td>
<td>none</td>
<td>augmentable</td>
<td>augmentable by schema import in prolog</td>
<td>module</td>
<td>Only one definition per global or local element name.</td>
</tr>
<tr>
<td>In-scope attribute declarations</td>
<td>none</td>
<td>augmentable</td>
<td>augmentable by schema import in prolog</td>
<td>module</td>
<td>Only one definition per global or local attribute name.</td>
</tr>
<tr>
<td>In-scope variables</td>
<td>none</td>
<td>augmentable</td>
<td>overwriteable and augmentable by prolog and by variable-binding
expressions</td>
<td>lexical</td>
<td>Only one definition per variable per lexical scope.</td>
</tr>
<tr>
<td>Function signatures</td>
<td>functions in <code>fn</code> namespace, and constructors for
built-in atomic types</td>
<td>augmentable</td>
<td class="diff-chg" title="XQ.E29" rowspan="1" colspan="1">
augmentable by module import and by function declaration in prolog;
augmentable by schema import (which adds constructor functions for
user-defined types)</td>
<td>module</td>
<td>Each function must have a unique expanded QName and number of
arguments.</td>
</tr>
<tr>
<td>Statically known collations</td>
<td>only the default collation</td>
<td>augmentable</td>
<td>no</td>
<td>module</td>
<td>Each URI uniquely identifies a collation.</td>
</tr>
<tr>
<td>Default collation</td>
<td>Unicode codepoint collation</td>
<td>overwriteable</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>None.</td>
</tr>
<tr>
<td>Construction mode</td>
<td><code>preserve</code></td>
<td>overwriteable</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>Value must be <code>preserve</code> or <code>strip</code>.</td>
</tr>
<tr>
<td>Ordering mode</td>
<td><code>ordered</code></td>
<td>overwriteable</td>
<td>overwriteable by prolog or expression</td>
<td>lexical</td>
<td>Value must be <code>ordered</code> or
<code>unordered</code>.</td>
</tr>
<tr>
<td>Default order for empty sequences</td>
<td>implementation-defined</td>
<td>overwriteable</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>Value must be <code>greatest</code> or <code>least</code>.</td>
</tr>
<tr>
<td>Boundary-space policy</td>
<td><code>strip</code></td>
<td>overwriteable</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>Value must be <code>preserve</code> or <code>strip</code>.</td>
</tr>
<tr>
<td>Copy-namespaces mode</td>
<td><code>inherit, preserve</code></td>
<td>overwriteable</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>Value consists of <code>inherit</code> or
<code>no-inherit</code>, and <code>preserve</code> or
<code>no-preserve</code>.</td>
</tr>
<tr>
<td>Base URI</td>
<td>See rules in <a href="#id-base-uri-decl"><b>4.5 Base URI
Declaration</b></a></td>
<td>overwriteable</td>
<td>overwriteable by prolog</td>
<td>module</td>
<td>Value must be a valid lexical representation of the type
xs:anyURI.</td>
</tr>
<tr>
<td>Statically known documents</td>
<td>none</td>
<td>augmentable</td>
<td>no</td>
<td>module</td>
<td>None.</td>
</tr>
<tr>
<td>Statically known collections</td>
<td>none</td>
<td>augmentable</td>
<td>no</td>
<td>module</td>
<td>None.</td>
</tr>
<tr>
<td>Statically known default collection type</td>
<td><code>node()*</code></td>
<td>overwriteable</td>
<td>no</td>
<td>module</td>
<td>None.</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="div2">
<h3><a name="id-xq-evaluation-context-components" id=
"id-xq-evaluation-context-components"></a>C.2 Dynamic Context
Components</h3>
<p>The following table describes the components of the <b>dynamic
context</b>. The following aspects of each component are
described:</p>
<ul>
<li>
<p><em>Default initial value:</em> This is the initial value of the
component if it is not overridden or augmented by the
implementation or by a query.</p>
</li>
<li>
<p><em>Can be overwritten or augmented by implementation:</em>
Indicates whether an XQuery implementation is allowed to replace
the default initial value of the component by a different <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> value
and/or to augment the default initial value by additional <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> values.</p>
</li>
<li>
<p><em>Can be overwritten or augmented by a query:</em> Indicates
whether a query is allowed to replace and/or augment the initial
value provided by default or by the implementation. If so,
indicates how this is accomplished.</p>
</li>
<li>
<p><em>Scope:</em> Indicates where the component is applicable.
"Global" indicates that the component applies globally, throughout
all the modules used in a query, and remains constant during
evaluation of a query. "Dynamic" indicates that evalation of an
expression may influence the value of the component for that
expression and for nested expressions.</p>
</li>
<li>
<p><em>Consistency Rules:</em> Indicates rules that must be
observed in assigning values to the component. Additional
consistency rules may be found in <a href=
"#id-consistency-constraints"><b>2.2.5 Consistency
Constraints</b></a>.</p>
</li>
</ul>
<div class="small">
<table width="100%" border="1" summary="Static Context" class=
"small">
<caption>Dynamic Context Components</caption>
<tbody>
<tr>
<th>Component</th>
<th>Default initial value</th>
<th>Can be overwritten or augmented by implementation?</th>
<th>Can be overwritten or augmented by a query?</th>
<th>Scope</th>
<th>Consistency rules</th>
</tr>
<tr>
<td>Context item</td>
<td>none</td>
<td>overwriteable</td>
<td>overwritten during evaluation of path expressions and
predicates</td>
<td>dynamic</td>
<td>None</td>
</tr>
<tr>
<td>Context position</td>
<td>none</td>
<td>overwriteable</td>
<td>overwritten during evaluation of path expressions and
predicates</td>
<td>dynamic</td>
<td>If context item is defined, context position must be &gt;0 and
&lt;= context size; else context position is <a title="undefined"
href="#dt-undefined">undefined</a>.</td>
</tr>
<tr>
<td>Context size</td>
<td>none</td>
<td>overwriteable</td>
<td>overwritten during evaluation of path expressions and
predicates</td>
<td>dynamic</td>
<td>If context item is defined, context size must be &gt;0; else
context size is <a title="undefined" href=
"#dt-undefined">undefined</a>.</td>
</tr>
<tr>
<td>Variable values</td>
<td>none</td>
<td>augmentable</td>
<td>overwriteable and augmentable by prolog and by variable-binding
expressions</td>
<td>dynamic</td>
<td>Names and values must be consistent with in-scope
variables.</td>
</tr>
<tr>
<td>Function implementations</td>
<td>functions in <code>fn</code> namespace, and constructors for
built-in atomic types</td>
<td>augmentable</td>
<td class="diff-chg" title="XQ.E29" rowspan="1" colspan="1">
augmentable by module import and by function declaration in prolog;
augmentable by schema import (which adds constructor functions for
user-defined types)</td>
<td>global</td>
<td>Must be consistent with function signatures</td>
</tr>
<tr>
<td>Current dateTime</td>
<td>none</td>
<td>must be initialized by implementation</td>
<td>no</td>
<td>global</td>
<td>Must include a timezone. Remains constant during evaluation of
a query.</td>
</tr>
<tr>
<td>Implicit timezone</td>
<td>none</td>
<td>must be initialized by implementation</td>
<td>no</td>
<td>global</td>
<td>Remains constant during evaluation of a query.</td>
</tr>
<tr>
<td>Available documents</td>
<td>none</td>
<td>must be initialized by implementation</td>
<td>no</td>
<td>global</td>
<td>None</td>
</tr>
<tr>
<td>Available collections</td>
<td>none</td>
<td>must be initialized by implementation</td>
<td>no</td>
<td>global</td>
<td>None</td>
</tr>
<tr>
<td>Default collection</td>
<td>none</td>
<td>overwriteable</td>
<td>no</td>
<td>global</td>
<td>None</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="div2">
<h3><a name="id-xq-serialization-parameters" id=
"id-xq-serialization-parameters"></a>C.3 Serialization
Parameters</h3>
<p>The following table specifies default values for the parameters
that control the process of serializing an <a title="XDM instance"
href="#dt-data-model-instance">XDM instance</a> into XML notation
(<code>method = "xml"</code>). The meanings of the various
parameters are defined in <a href="#serialization">[XSLT 2.0 and
XQuery 1.0 Serialization (Second Edition)]</a>. For each parameter,
an XQuery implementation may (but is not required to) provide a
means whereby a user can override the default value.</p>
<div class="small">
<table border="1" width="60%" summary="Unary operators" class=
"small">
<caption>Serialization Parameters</caption>
<tbody>
<tr>
<th>Parameter</th>
<th>Default Value</th>
</tr>
<tr>
<td>byte-order-mark</td>
<td>implementation-defined</td>
</tr>
<tr>
<td>cdata-section-elements</td>
<td>empty</td>
</tr>
<tr>
<td>doctype-public</td>
<td>(none)</td>
</tr>
<tr>
<td>doctype-system</td>
<td>(none)</td>
</tr>
<tr>
<td>encoding</td>
<td>implementation-defined choice between "utf-8" and "utf-16"</td>
</tr>
<tr>
<td>escape-uri-attributes</td>
<td>(not applicable when method = xml)</td>
</tr>
<tr>
<td>include-content-type</td>
<td>(not applicable when method = xml)</td>
</tr>
<tr>
<td>indent</td>
<td>no</td>
</tr>
<tr>
<td>media-type</td>
<td>implementation-defined</td>
</tr>
<tr>
<td>method</td>
<td>xml</td>
</tr>
<tr>
<td>normalization-form</td>
<td>implementation-defined</td>
</tr>
<tr>
<td>omit-xml-declaration</td>
<td>implementation-defined</td>
</tr>
<tr>
<td>standalone</td>
<td>implementation-defined</td>
</tr>
<tr>
<td>undeclare-prefixes</td>
<td>no</td>
</tr>
<tr>
<td>use-character-maps</td>
<td>empty</td>
</tr>
<tr>
<td>version</td>
<td>implementation-defined</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
</div>
<div class="div1">
<h2><a name="id-impl-defined-items" id=
"id-impl-defined-items"></a>D Implementation-Defined Items</h2>
<p>The following items in this specification are <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>:</p>
<ol class="enumar">
<li>
<p>The version of Unicode that is used to construct
expressions.</p>
</li>
<li>
<p>The <a title="statically known collations" href=
"#dt-static-collations">statically-known collations</a>.</p>
</li>
<li>
<p>The <a title="implicit timezone" href="#dt-timezone">implicit
timezone</a>.</p>
</li>
<li>
<p>The circumstances in which <a title="warning" href=
"#dt-warning">warnings</a> are raised, and the ways in which
warnings are handled.</p>
</li>
<li>
<p>The method by which errors are reported to the external
processing environment.</p>
</li>
<li>
<p>Whether the implementation is based on the rules of <a href=
"#XML">[XML 1.0]</a> and <a href="#XMLNAMES">[XML Names]</a> or the
rules of <a href="#XML1.1">[XML 1.1]</a> and <a href=
"#XMLNAMES11">[XML Names 1.1]</a>. One of these sets of rules must
be applied consistently by all aspects of the implementation. If
the implementation is based on the rules of <a href="#XML">[XML
1.0]</a>, the edition used must be at least Third Edition; the
edition used is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>, but we
recommend that implementations use the latest version.</p>
</li>
<li class="xquery">
<p>Any components of the <a title="static context" href=
"#dt-static-context">static context</a> or <a title=
"dynamic context" href="#dt-dynamic-context">dynamic context</a>
that are overwritten or augmented by the implementation.</p>
</li>
<li class="xquery">
<p>Which of the <a title="optional axis" href=
"#dt-optional-axis">optional axes</a> are supported by the
implementation, if the <a title="Full Axis Feature" href=
"#dt-full-axis-feature">Full-Axis Feature</a> is not supported.</p>
</li>
<li class="xquery">
<p>The default handling of empty sequences returned by an ordering
key (sortspec) in an <code>order by</code> clause (<code>empty
least</code> or <code>empty greatest</code>).</p>
</li>
<li class="xquery">
<p>The names and semantics of any <a title="extension expression"
href="#dt-extension-expression">extension expressions</a>
(<a title="pragma" href="#dt-pragma">pragmas</a>) recognized by the
implementation.</p>
</li>
<li class="xquery">
<p>The names and semantics of any <a title="option declaration"
href="#dt-option-declaration">option declarations</a> recognized by
the implementation.</p>
</li>
<li class="xquery">
<p>Protocols (if any) by which parameters can be passed to an
external function, and the result of the function can returned to
the invoking query.</p>
</li>
<li class="xquery">
<p>The process by which the specific modules to be imported by a
<a title="module import" href="#dt-module-import">module import</a>
are identified, if the <a title="module feature" href=
"#dt-module-feature">Module Feature</a> is supported (includes
processing of location hints, if any.)</p>
</li>
<li class="xquery">
<p>Any <a title="static typing extension" href=
"#dt-static-typing-extension">static typing extensions</a>
supported by the implementation, if the <a title=
"static typing feature" href="#dt-static-typing-feature">Static
Typing Feature</a> is supported.</p>
</li>
<li class="xquery">
<p>The means by which serialization is invoked, if the <a title=
"serialization feature" href=
"#dt-serialization-feature">Serialization Feature</a> is
supported.</p>
</li>
<li class="xquery">
<p>The default values for the <code>byte-order-mark</code>,
<code>encoding</code>, <code>media-type</code>,
<code>normalization-form</code>, <code>omit-xml-declaration</code>,
<code>standalone</code>, and <code>version</code> parameters, if
the <a title="serialization feature" href=
"#dt-serialization-feature">Serialization Feature</a> is
supported.</p>
</li>
<li class="xquery">
<p>The result of an unsuccessful call to an external function (for
example, if the function implementation cannot be found or does not
return a value of the declared type).</p>
</li>
<li class="xquery">
<p>Limits on ranges of values for various data types, as enumerated
in <a href="#id-data-model-conformance"><b>5.3 Data Model
Conformance</b></a>.</p>
</li>
<li class="xquery">
<p>Syntactic extensions to XQuery, including both their syntax and
semantics, as discussed in <a href="#id-syntax-extensions"><b>5.4
Syntax Extensions</b></a>.</p>
</li>
</ol>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>Additional <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> items are
listed in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data Model
(Second Edition)]</a> and <a href="#FunctionsAndOperators">[XQuery
1.0 and XPath 2.0 Functions and Operators (Second
Edition)]</a>.</p>
</div>
</div>
<div class="div1">
<h2><a name="id-references" id="id-references"></a>E
References</h2>
<div class="div2">
<h3><a name="id-normative-references" id=
"id-normative-references"></a>E.1 Normative References</h3>
<dl>
<dt class="label"><span><a name="RFC2119" id="RFC2119"></a>RFC
2119</span></dt>
<dd>
<div>S. Bradner. <em>Key Words for use in RFCs to Indicate
Requirement Levels.</em> IETF RFC 2119. See <a href=
"http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>.</div>
</dd>
<dt class="label"><span><a name="RFC3986" id=
"RFC3986"></a>RFC3986</span></dt>
<dd>
<div>T. Berners-Lee, R. Fielding, and L. Masinter. <em>Uniform
Resource Identifiers (URI): Generic Syntax</em>. IETF RFC 3986. See
<a href=
"http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3986.txt</a>.</div>
</dd>
<dt class="label"><span><a name="RFC3987" id=
"RFC3987"></a>RFC3987</span></dt>
<dd>
<div>M. Duerst and M. Suignard. <em>Internationalized Resource
Identifiers (IRIs)</em>. IETF RFC 3987. See <a href=
"http://www.ietf.org/rfc/rfc3987.txt">http://www.ietf.org/rfc/rfc3987.txt</a>.</div>
</dd>
<dt class="label"><span><a name="ISO10646" id=
"ISO10646"></a>ISO/IEC 10646</span></dt>
<dd>
<div>ISO (International Organization for Standardization).
<em>ISO/IEC 10646:2003. Information technology—Universal
Multiple-Octet Coded Character Set (UCS)</em>, as, from time to
time, amended, replaced by a new edition, or expanded by the
addition of new parts. [Geneva]: International Organization for
Standardization. (See <a href=
"http://www.iso.org">http://www.iso.org</a> for the latest
version.)</div>
</dd>
<dt class="label"><span><a name="Unicode" id=
"Unicode"></a>Unicode</span></dt>
<dd>
<div>The Unicode Consortium. <em>The Unicode Standard</em> Reading,
Mass.: Addison-Wesley, 2003, as updated from time to time by the
publication of new versions. See <a href=
"http://www.unicode.org/standard/versions/">http://www.unicode.org/standard/versions/</a>
for the latest version and additional information on versions of
the standard and of the Unicode Character Database. The version of
Unicode to be used is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>, but
implementations are recommended to use the latest Unicode
version.</div>
</dd>
<dt class="label"><a name="XML" id="XML"></a>XML 1.0</dt>
<dd>World Wide Web Consortium. <em>Extensible Markup Language (XML)
1.0.</em> W3C Recommendation. See <a href=
"http://www.w3.org/TR/REC-xml/">http://www.w3.org/TR/REC-xml/</a>.
The edition of XML 1.0 must be no earlier than the Third Edition;
the edition used is <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>, but we
recommend that implementations use the latest version.</dd>
<dt class="label"><span><a name="XML1.1" id="XML1.1"></a>XML
1.1</span></dt>
<dd>
<div>World Wide Web Consortium. <em>Extensible Markup Language
(XML) 1.1.</em> W3C Recommendation. See <a href=
"http://www.w3.org/TR/xml11/">http://www.w3.org/TR/xml11/</a></div>
</dd>
<dt class="label"><span><a name="XMLBASE" id="XMLBASE"></a>XML
Base</span></dt>
<dd>
<div>World Wide Web Consortium. <em>XML Base.</em> W3C
Recommendation. See <a href=
"http://www.w3.org/TR/xmlbase/">http://www.w3.org/TR/xmlbase/</a></div>
</dd>
<dt class="label"><span><a name="XMLNAMES" id="XMLNAMES"></a>XML
Names</span></dt>
<dd>
<div>World Wide Web Consortium. <em>Namespaces in XML.</em> W3C
Recommendation. See <a href=
"http://www.w3.org/TR/REC-xml-names/">http://www.w3.org/TR/REC-xml-names/</a></div>
</dd>
<dt class="label"><span><a name="XMLNAMES11" id=
"XMLNAMES11"></a>XML Names 1.1</span></dt>
<dd>
<div>World Wide Web Consortium. <em>Namespaces in XML 1.1.</em> W3C
Recommendation. See <a href=
"http://www.w3.org/TR/xml-names11/">http://www.w3.org/TR/xml-names11/</a></div>
</dd>
<dt class="label"><span><a name="XMLID" id="XMLID"></a>XML
ID</span></dt>
<dd>
<div>World Wide Web Consortium. <em>xml:id Version 1.0.</em> W3C
Recommendation. See <a href=
"http://www.w3.org/TR/xml-id/">http://www.w3.org/TR/xml-id/</a></div>
</dd>
<dt class="label"><span><a name="XMLSchema" id="XMLSchema"></a>XML
Schema</span></dt>
<dd>
<div>World Wide Web Consortium. <em>XML Schema, Parts 0, 1, and 2
(Second Edition)</em>. W3C Recommendation, 28 October 2004. See
<a href=
"http://www.w3.org/TR/xmlschema-0/">http://www.w3.org/TR/xmlschema-0/</a>,
<a href=
"http://www.w3.org/TR/xmlschema-1/">http://www.w3.org/TR/xmlschema-1/</a>,
and <a href=
"http://www.w3.org/TR/xmlschema-2/">http://www.w3.org/TR/xmlschema-2/</a>.</div>
</dd>
<dt class="label"><a name="datamodel" id="datamodel"></a>XQuery 1.0
and XPath 2.0 Data Model (Second Edition)</dt>
<dd>World Wide Web Consortium. <em>XQuery 1.0 and XPath 2.0 Data
Model (XDM) (Second Edition)</em>. W3C Recommendation, 14 December
2010. See <a href=
"http://www.w3.org/TR/xpath-datamodel/">http://www.w3.org/TR/xpath-datamodel/</a>.</dd>
<dt class="label"><a name="XQueryFormalSemantics" id=
"XQueryFormalSemantics"></a>XQuery 1.0 and XPath 2.0 Formal
Semantics (Second Edition)</dt>
<dd>World Wide Web Consortium. <em>XQuery 1.0 and XPath 2.0 Formal
Semantics (Second Edition)</em>. W3C Recommendation, 14 December
2010. See <a href=
"http://www.w3.org/TR/xquery-semantics/">http://www.w3.org/TR/xquery-semantics/</a>.</dd>
<dt class="label"><a name="FunctionsAndOperators" id=
"FunctionsAndOperators"></a>XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)</dt>
<dd>World Wide Web Consortium. <em>XQuery 1.0 and XPath 2.0
Functions and Operators (Second Edition)</em> W3C Recommendation,
14 December 2010. See <a href=
"http://www.w3.org/TR/xquery-operators/">http://www.w3.org/TR/xpath-functions/</a>.</dd>
<dt class="label"><a name="serialization" id=
"serialization"></a>XSLT 2.0 and XQuery 1.0 Serialization (Second
Edition)</dt>
<dd>World Wide Web Consortium. <em>XSLT 2.0 and XQuery 1.0
Serialization (Second Edition)</em>. W3C Recommendation, 14
December 2010. See <a href=
"http://www.w3.org/TR/xslt-xquery-serialization/">http://www.w3.org/TR/xslt-xquery-serialization/</a>.</dd>
</dl>
</div>
<div class="div2">
<h3><a name="id-non-normative-references" id=
"id-non-normative-references"></a>E.2 Non-normative References</h3>
<dl>
<dt class="label"><span class="xquery"><a name="Requirements" id=
"Requirements"></a>XML Query 1.0 Requirements</span></dt>
<dd>
<div class="xquery">World Wide Web Consortium. <em>XML Query 1.0
Requirements</em>. W3C Working Draft, 14 Nov 2003. See <a href=
"http://www.w3.org/TR/xquery-requirements/">http://www.w3.org/TR/xquery-requirements/</a>.</div>
</dd>
<dt class="label"><a name="XPath20" id="XPath20"></a>XML Path
Language (XPath) 2.0 (Second Edition)</dt>
<dd>World Wide Web Consortium. <em>XML Path Language (XPath)
Version 2.0 (Second Edition)</em>. W3C Recommendation, 14 December
2010. See <a href=
"http://www.w3.org/TR/xpath20/">http://www.w3.org/TR/xpath20/</a>.</dd>
<dt class="label"><a name="XQueryX" id="XQueryX"></a>XML Syntax for
XQuery 1.0 (XQueryX) (Second Edition)</dt>
<dd>World Wide Web Consortium. <em>XQueryX, Version 1.0 (Second
Edition)</em>. W3C Recommendation, 14 December 2010. See <a href=
"http://www.w3.org/TR/xqueryx/">http://www.w3.org/TR/xqueryx/</a>.</dd>
<dt class="label"><a name="XSLT" id="XSLT"></a>XSL Transformations
(XSLT) Version 2.0 (Second Edition)</dt>
<dd>World Wide Web Consortium. <em>XSL Transformations (XSLT) 2.0
(Second Edition)</em> W3C Recommendation, 14 December 2010. See
<a href=
"http://www.w3.org/TR/xslt20/">http://www.w3.org/TR/xslt20/</a></dd>
<dt class="label"><span><a name="DOM" id="DOM"></a>Document Object
Model</span></dt>
<dd>
<div>World Wide Web Consortium. <em>Document Object Model (DOM)
Level 3 Core Specification.</em> W3C Recommendation, April 7, 2004.
See <a href=
"http://www.w3.org/TR/DOM-Level-3-Core/">http://www.w3.org/TR/DOM-Level-3-Core/</a>.</div>
</dd>
<dt class="label"><span><a name="XINFO" id="XINFO"></a>XML
Infoset</span></dt>
<dd>
<div>World Wide Web Consortium. <em>XML Information Set.</em> W3C
Recommendation 24 October 2001. See <a href=
"http://www.w3.org/TR/xml-infoset/">http://www.w3.org/TR/xml-infoset/</a></div>
</dd>
<dt class="label"><span><a name="XPath" id="XPath"></a>XPath
1.0</span></dt>
<dd>
<div>World Wide Web Consortium. <em>XML Path Language (XPath)
Version 1.0</em>. W3C Recommendation, Nov. 16, 1999. See <a href=
"http://www.w3.org/TR/xpath/">http://www.w3.org/TR/xpath/</a></div>
</dd>
<dt class="label"><span><a name="XPTR" id=
"XPTR"></a>XPointer</span></dt>
<dd>
<div>World Wide Web Consortium. <em>XML Pointer Language
(XPointer).</em> W3C Last Call Working Draft 8 January 2001. See
<a href=
"http://www.w3.org/TR/WD-xptr">http://www.w3.org/TR/WD-xptr</a></div>
</dd>
<dt class="label"><span class="xquery"><a name="UseCases" id=
"UseCases"></a>XML Query Use Cases</span></dt>
<dd>
<div class="xquery">World Wide Web Consortium. <em>XML Query Use
Cases</em>. W3C Working Draft, 8 June 2006. See <a href=
"http://www.w3.org/TR/xquery-use-cases/">http://www.w3.org/TR/xquery-use-cases/</a>.</div>
</dd>
<dt class="label"><span class="xquery"><a name="xml11schema10" id=
"xml11schema10"></a>XML 1.1 and Schema 1.0</span></dt>
<dd>
<div class="xquery">World Wide Web Consortium. <em>Processing XML
1.0 Documents with XML Schema 1.0 Processors</em>. W3C Working
Group Note, 11 May 2005. See <a href=
"http://www.w3.org/TR/xml11schema10/">http://www.w3.org/TR/xml11schema10/</a>.</div>
</dd>
<dt class="label"><span class="xquery"><a name="RFC1738" id=
"RFC1738"></a>Uniform Resource Locators (URL)</span></dt>
<dd>
<div class="xquery">Internet Engineering Task Force (IETF).
<em>Uniform Resource Locators (URL)</em>. Request For Comment No.
1738, Dec. 1994. See <a href=
"http://www.ietf.org/rfc/rfc1738.txt">http://www.ietf.org/rfc/rfc1738.txt</a>.</div>
</dd>
<dt class="label"><span class="xquery"><a name="ODMG" id=
"ODMG"></a>ODMG</span></dt>
<dd>
<div class="xquery">Rick Cattell et al. <em>The Object Database
Standard: ODMG-93, Release 1.2</em>. Morgan Kaufmann Publishers,
San Francisco, 1996.</div>
</dd>
<dt class="label"><span class="xquery"><a name="Quilt" id=
"Quilt"></a>Quilt</span></dt>
<dd>
<div class="xquery">Don Chamberlin, Jonathan Robie, and Daniela
Florescu. <em>Quilt: an XML Query Language for Heterogeneous Data
Sources</em>. In <em>Lecture Notes in Computer Science</em>,
Springer-Verlag, Dec. 2000. Also available at <a href=
"http://www.almaden.ibm.com/cs/people/chamberlin/quilt_lncs.pdf">http://www.almaden.ibm.com/cs/people/chamberlin/quilt_lncs.pdf</a>.
See also <a href=
"http://www.almaden.ibm.com/cs/people/chamberlin/quilt.html">http://www.almaden.ibm.com/cs/people/chamberlin/quilt.html</a>.</div>
</dd>
<dt class="label"><span class="xquery"><a name="XML-QL" id=
"XML-QL"></a>XML-QL</span></dt>
<dd>
<div class="xquery">Alin Deutsch, Mary Fernandez, Daniela Florescu,
Alon Levy, and Dan Suciu. <em>A Query Language for XML</em>.</div>
</dd>
<dt class="label"><span class="xquery"><a name="SQL" id=
"SQL"></a>SQL</span></dt>
<dd>
<div class="xquery">International Organization for Standardization
(ISO). <em>Information Technology-Database Language SQL</em>.
Standard No. ISO/IEC 9075:2003. (Available from American National
Standards Institute, New York, NY 10036, (212) 642-4900.)</div>
</dd>
<dt class="label"><span class="xquery"><a name="XQL" id=
"XQL"></a>XQL</span></dt>
<dd>
<div class="xquery">J. Robie, J. Lapp, D. Schach. <em>XML Query
Language (XQL)</em>. See <a href=
"http://www.w3.org/TandS/QL/QL98/pp/xql.html">http://www.w3.org/TandS/QL/QL98/pp/xql.html</a>.</div>
</dd>
</dl>
</div>
<div class="div2">
<h3><a name="id-background-material" id=
"id-background-material"></a>E.3 Background Material</h3>
<dl>
<dt class="label"><span><a name="CHARMOD" id=
"CHARMOD"></a>Character Model</span></dt>
<dd>
<div>World Wide Web Consortium. <em>Character Model for the World
Wide Web.</em> W3C Working Draft. See <a href=
"http://www.w3.org/TR/charmod/">http://www.w3.org/TR/charmod/</a>.</div>
</dd>
<dt class="label"><span><a name="XSLT1" id="XSLT1"></a>XSLT
1.0</span></dt>
<dd>
<div>World Wide Web Consortium. <em>XSL Transformations (XSLT)
1.0.</em> W3C Recommendation. See <a href=
"http://www.w3.org/TR/xslt">http://www.w3.org/TR/xslt</a></div>
</dd>
<dt class="label"><span class="xquery"><a name="UseCaseQueries" id=
"UseCaseQueries"></a>Use Case Sample Queries</span></dt>
<dd>
<div class="xquery">Queries from the XQuery 1.0 Use Cases,
presented in a single file. See <a href=
"http://www.w3.org/TR/xquery-use-cases/xquery-use-case-queries.txt">
http://www.w3.org/TR/xquery-use-cases/xquery-use-case-queries.txt</a>.</div>
</dd>
<dt class="label"><span class="xquery"><a name="XQueryQueries" id=
"XQueryQueries"></a>XQuery Sample Queries</span></dt>
<dd>
<div class="xquery">Queries from this document, presented in a
single file. See <a href=
"http://www.w3.org/TR/xquery-use-cases/xquery-wd-queries.txt">http://www.w3.org/TR/xquery-use-cases/xquery-wd-queries.txt</a>.</div>
</dd>
</dl>
</div>
</div>
<div class="div1">
<h2><a name="id-errors" id="id-errors"></a>F Error Conditions</h2>
<dl>
<dt><a name="ERRXPST0001" id="ERRXPST0001"></a>err:XPST0001</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if analysis of an expression relies on some component of
the <a title="static context" href="#dt-static-context">static
context</a> that has not been assigned a value.</p>
</dd>
<dt><a name="ERRXPDY0002" id="ERRXPDY0002"></a>err:XPDY0002</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if evaluation of an
expression relies on some part of the <a title="dynamic context"
href="#dt-dynamic-context">dynamic context</a> that has not been
assigned a value.</p>
</dd>
<dt><a name="ERRXPST0003" id="ERRXPST0003"></a>err:XPST0003</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if an expression is not a valid instance of the grammar
defined in <a href="#id-grammar"><b>A.1 EBNF</b></a>.</p>
</dd>
<dt><a name="ERRXPTY0004" id="ERRXPTY0004"></a>err:XPTY0004</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if, during the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a>, an expression is
found to have a <a title="static type" href=
"#dt-static-type">static type</a> that is not appropriate for the
context in which the expression occurs, or during the <a title=
"dynamic evaluation phase" href="#dt-dynamic-evaluation">dynamic
evaluation phase</a>, the <a title="dynamic type" href=
"#dt-dynamic-type">dynamic type</a> of a value does not match a
required type as specified by the matching rules in <a href=
"#id-sequencetype-matching"><b>2.5.4 SequenceType
Matching</b></a>.</p>
</dd>
<dt><a name="ERRXPST0005" id="ERRXPST0005"></a>err:XPST0005</dt>
<dd>
<p>During the analysis phase, it is a <a title="static error" href=
"#dt-static-error">static error</a> if the <a title="static type"
href="#dt-static-type">static type</a> assigned to an expression
other than the expression <code>()</code> or <code>data(())</code>
is <code>empty-sequence()</code>.</p>
</dd>
<dt><a name="ERRXPTY0006" id="ERRXPTY0006"></a>err:XPTY0006</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXPTY0007" id="ERRXPTY0007"></a>err:XPTY0007</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXPST0008" id="ERRXPST0008"></a>err:XPST0008</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if an expression refers to an element name, attribute
name, schema type name, namespace prefix, or variable name that is
not defined in the <a title="static context" href=
"#dt-static-context">static context</a>, except for an ElementName
in an <a href="#doc-xquery-ElementTest">ElementTest</a> or an
AttributeName in an <a href=
"#doc-xquery-AttributeTest">AttributeTest</a>.</p>
</dd>
<dt><a name="ERRXQST0009" id="ERRXQST0009"></a>err:XQST0009</dt>
<dd>
<p>An implementation that does not support the Schema Import
Feature must raise a <a title="static error" href=
"#dt-static-error">static error</a> if a Prolog contains a schema
import.</p>
</dd>
<dt><a name="ERRXPST0010" id="ERRXPST0010"></a>err:XPST0010</dt>
<dd>
<p>An implementation must raise a <a title="static error" href=
"#dt-static-error">static error</a> if it encounters a reference to
an axis that it does not support.</p>
</dd>
<dt><a name="ERRXQST0012" id="ERRXQST0012"></a>err:XQST0012</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the set of definitions contained in all schemas
imported by a Prolog do not satisfy the conditions for schema
validity specified in Sections 3 and 5 of <a href="#XMLSchema">[XML
Schema]</a> Part 1--i.e., each definition must be valid, complete,
and unique.</p>
</dd>
<dt><a name="ERRXQST0013" id="ERRXQST0013"></a>err:XQST0013</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if an implementation recognizes a pragma but determines
that its content is invalid.</p>
</dd>
<dt><a name="ERRXQST0014" id="ERRXQST0014"></a>err:XQST0014</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0015" id="ERRXQST0015"></a>err:XQST0015</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0016" id="ERRXQST0016"></a>err:XQST0016</dt>
<dd>
<p>An implementation that does not support the Module Feature
raises a <a title="static error" href="#dt-static-error">static
error</a> if it encounters a <a title="module declaration" href=
"#dt-module-declaration">module declaration</a> or a <a title=
"module import" href="#dt-module-import">module import</a>.</p>
</dd>
<dt><a name="ERRXPST0017" id="ERRXPST0017"></a>err:XPST0017</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the expanded QName and number of arguments in a
function call do not match the name and arity of a <a title=
"function signature" href="#dt-function-signature">function
signature</a> in the <a title="static context" href=
"#dt-static-context">static context</a>.</p>
</dd>
<dt><a name="ERRXPTY0018" id="ERRXPTY0018"></a>err:XPTY0018</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if the result of the last step in a path expression
contains both nodes and atomic values.</p>
</dd>
<dt><a name="ERRXPTY0019" id="ERRXPTY0019"></a>err:XPTY0019</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if the result of a step (other than the last step) in a
path expression contains an atomic value.</p>
</dd>
<dt><a name="ERRXPTY0020" id="ERRXPTY0020"></a>err:XPTY0020</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if, in an axis step, the context item is not a node.</p>
</dd>
<dt><a name="ERRXPDY0021" id="ERRXPDY0021"></a>err:XPDY0021</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0022" id="ERRXQST0022"></a>err:XQST0022</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the value of a <a title=
"namespace declaration attribute" href=
"#dt-namespace-decl-attr">namespace declaration attribute</a> is
not a <a href="#doc-xquery-URILiteral">URILiteral</a>.</p>
</dd>
<dt><a name="ERRXQTY0023" id="ERRXQTY0023"></a>err:XQTY0023</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQTY0024" id="ERRXQTY0024"></a>err:XQTY0024</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if the content sequence in an element constructor
contains an attribute node following a node that is not an
attribute node.</p>
</dd>
<dt><a name="ERRXQDY0025" id="ERRXQDY0025"></a>err:XQDY0025</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if any attribute of a
constructed element does not have a name that is distinct from the
names of all other attributes of the constructed element.</p>
</dd>
<dt><a name="ERRXQDY0026" id="ERRXQDY0026"></a>err:XQDY0026</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the result of the content
expression of a computed processing instruction constructor
contains the string "<code>?&gt;</code>".</p>
</dd>
<dt><a name="ERRXQDY0027" id="ERRXQDY0027"></a>err:XQDY0027</dt>
<dd>
<p>In a validate expression, it is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the root element
information item in the PSVI resulting from validation does not
have the expected validity property: <code>valid</code> if
validation mode is <code>strict</code>, or either
<code>valid</code> or <code>notKnown</code> if validation mode is
<code>lax</code>.</p>
</dd>
<dt><a name="ERRXQTY0028" id="ERRXQTY0028"></a>err:XQTY0028</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQDY0029" id="ERRXQDY0029"></a>err:XQDY0029</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQTY0030" id="ERRXQTY0030"></a>err:XQTY0030</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if the argument of a <code>validate</code> expression
does not evaluate to exactly one document or element node.</p>
</dd>
<dt><a name="ERRXQST0031" id="ERRXQST0031"></a>err:XQST0031</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the version number specified in a version declaration
is not supported by the implementation.</p>
</dd>
<dt><a name="ERRXQST0032" id="ERRXQST0032"></a>err:XQST0032</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if a Prolog contains more than one <a title=
"base URI declaration" href="#dt-base-uri-decl">base URI
declaration</a>.</p>
</dd>
<dt><a name="ERRXQST0033" id="ERRXQST0033"></a>err:XQST0033</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a module contains multiple bindings for the same
namespace prefix.</p>
</dd>
<dt><a name="ERRXQST0034" id="ERRXQST0034"></a>err:XQST0034</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if multiple functions declared or imported by a <a title=
"module" href="#dt-module">module</a> have the <span>same</span>
number of arguments and their expanded QNames are equal (as defined
by the <code>eq</code> operator).</p>
</dd>
<dt><a name="ERRXQST0035" id="ERRXQST0035"></a>err:XQST0035</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> to import two schema components that both define the same
name in the same symbol space and in the same scope.</p>
</dd>
<dt><a name="ERRXQST0036" id="ERRXQST0036"></a>err:XQST0036</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> to import a module if the <a title=
"in-scope schema definitions" href="#dt-issd">in-scope schema
definitions</a> of the importing module do not include all of the
following:</p>
<ol class="enumar">
<li>
<p>An <a title="in-scope schema type" href="#dt-is-types">in-scope
schema type</a> for each type-name that appears:</p>
<ol class="enumla">
<li>
<p>in the type of a variable that is declared in the imported
module and referenced in the importing module, OR</p>
</li>
<li>
<p>in a parameter-type or result-type of a function that is
declared in the imported module and referenced in the importing
module.</p>
</li>
</ol>
</li>
<li>
<p>An <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declaration</a> for each
element-name <code>EN</code> such that:</p>
<ol class="enumla">
<li>
<p><code>schema-element(EN)</code> appears in the declared type of
a variable in the imported module, and that variable is referenced
in the importing module, OR</p>
</li>
<li>
<p><code>schema-element(EN)</code> appears in a parameter-type or
result-type of a function declared in the imported module, and that
function is referenced in the importing module.</p>
</li>
</ol>
</li>
<li>
<p>An <a title="in-scope attribute declarations" href=
"#dt-is-attrs">in-scope attribute declaration</a> for each
attribute-name <code>AN</code> such that:</p>
<ol class="enumla">
<li>
<p><code>schema-attribute(AN)</code> appears in the declared type
of a variable in the imported module, and that variable is
referenced in the importing module, OR</p>
</li>
<li>
<p><code>schema-attribute(AN)</code> appears in a parameter-type or
result-type of a function declared in the imported module, and that
function is referenced in the importing module.</p>
</li>
</ol>
</li>
</ol>
</dd>
<dt><a name="ERRXQST0037" id="ERRXQST0037"></a>err:XQST0037</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0038" id="ERRXQST0038"></a>err:XQST0038</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a Prolog contains more than one <a title=
"default collation declaration" href=
"#dt-default-collation-decl">default collation declaration</a>, or
the value specified by a default collation declaration is not
present in <a title="statically known collations" href=
"#dt-static-collations">statically known collations</a>.</p>
</dd>
<dt><a name="ERRXQST0039" id="ERRXQST0039"></a>err:XQST0039</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> for a function declaration to have more than one
parameter with the same name.</p>
</dd>
<dt><a name="ERRXQST0040" id="ERRXQST0040"></a>err:XQST0040</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the attributes specified by a direct element
constructor do not have distinct expanded QNames.</p>
</dd>
<dt><a name="ERRXQDY0041" id="ERRXQDY0041"></a>err:XQDY0041</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the value of the name
expression in a computed processing instruction constructor cannot
be cast to the type <code>xs:NCName</code>.</p>
</dd>
<dt><a name="ERRXQST0042" id="ERRXQST0042"></a>err:XQST0042</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0043" id="ERRXQST0043"></a>err:XQST0043</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQDY0044" id="ERRXQDY0044"></a>err:XQDY0044</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">dynamic
error</a> the node-name of a node constructed by a computed
attribute constructor has any of the following properties:</p>
<ul>
<li>
<p>Its namespace prefix is <code>xmlns</code>.</p>
</li>
<li>
<p>It has no namespace prefix and its local name is
<code>xmlns</code>.</p>
</li>
<li>
<p>Its namespace URI is
<code>http://www.w3.org/2000/xmlns/</code>.</p>
</li>
<li>
<p>Its namespace prefix is <code>xml</code> and its namespace URI
is not <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>Its namespace prefix is other than <code>xml</code> and its
namespace URI is
<code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
</ul>
</dd>
<dt><a name="ERRXQST0045" id="ERRXQST0045"></a>err:XQST0045</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the function name in a function declaration is in one
of the following namespaces:
<code>http://www.w3.org/XML/1998/namespace,
http://www.w3.org/2001/XMLSchema,
http://www.w3.org/2001/XMLSchema-instance,
http://www.w3.org/2005/xpath-functions</code>.</p>
</dd>
<dt><a name="ERRXQST0046" id="ERRXQST0046"></a>err:XQST0046</dt>
<dd>
<p>An implementation <a title="may" href="#may">MAY</a> raise a
<a title="static error" href="#dt-static-error">static error</a> if
the value of a <a href="#doc-xquery-URILiteral">URILiteral</a> is
of nonzero length and is not in the lexical space of
<code>xs:anyURI</code>.</p>
</dd>
<dt><a name="ERRXQST0047" id="ERRXQST0047"></a>err:XQST0047</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if multiple module imports in the same Prolog specify the
same target namespace.</p>
</dd>
<dt><a name="ERRXQST0048" id="ERRXQST0048"></a>err:XQST0048</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a function or variable declared in a library module is
not in the target namespace of the library module.</p>
</dd>
<dt><a name="ERRXQST0049" id="ERRXQST0049"></a>err:XQST0049</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if two or more variables declared or imported by a
<a title="module" href="#dt-module">module</a> have equal expanded
QNames (as defined by the <code>eq</code> operator.)</p>
</dd>
<dt><a name="ERRXPDY0050" id="ERRXPDY0050"></a>err:XPDY0050</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a> of the
operand of a <code>treat</code> expression does not match the
<a title="sequence type" href="#dt-sequence-type">sequence type</a>
specified by the <code>treat</code> expression. This error might
also be raised by a path expression beginning with "<code>/</code>"
or "<code>//</code>" if the context node is not in a tree that is
rooted at a document node. This is because a leading
"<code>/</code>" or "<code>//</code>" in a path expression is an
abbreviation for an initial step that includes the clause
<code>treat as document-node()</code>.</p>
</dd>
<dt><a name="ERRXPST0051" id="ERRXPST0051"></a>err:XPST0051</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a QName that is used as an <a href=
"#doc-xquery-AtomicType">AtomicType</a> in a <a href=
"#doc-xquery-SequenceType">SequenceType</a> is not defined in the
<a title="in-scope schema type" href="#dt-is-types">in-scope schema
types</a> as an atomic type.</p>
</dd>
<dt><a name="ERRXQDY0052" id="ERRXQDY0052"></a>err:XQDY0052</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0053" id="ERRXQST0053"></a>err:XQST0053</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0054" id="ERRXQST0054"></a>err:XQST0054</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a variable <a title="variable depends" href=
"#dt-variable-depends">depends</a> on itself.</p>
</dd>
<dt><a name="ERRXQST0055" id="ERRXQST0055"></a>err:XQST0055</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a Prolog contains more than one <a title=
"copy-namespaces declaration" href=
"#dt-copy-namespaces-decl">copy-namespaces declaration</a>.</p>
</dd>
<dt><a name="ERRXQST0056" id="ERRXQST0056"></a>err:XQST0056</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0057" id="ERRXQST0057"></a>err:XQST0057</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a schema import binds a namespace prefix but does not
specify a target namespace other than a zero-length string.</p>
</dd>
<dt><a name="ERRXQST0058" id="ERRXQST0058"></a>err:XQST0058</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if multiple schema imports specify the same target
namespace.</p>
</dd>
<dt><a name="ERRXQST0059" id="ERRXQST0059"></a>err:XQST0059</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if an implementation is unable to process a schema or
module import by finding a schema or module with the specified
target namespace.</p>
</dd>
<dt><a name="ERRXQST0060" id="ERRXQST0060"></a>err:XQST0060</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the name of a function in a function declaration is
not in a namespace (expanded QName has a null namespace URI).</p>
</dd>
<dt><a name="ERRXQDY0061" id="ERRXQDY0061"></a>err:XQDY0061</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the operand of a validate
expression is a document node whose children do not consist of
exactly one element node and zero or more comment and processing
instruction nodes, in any order.</p>
</dd>
<dt><a name="ERRXQDY0062" id="ERRXQDY0062"></a>err:XQDY0062</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0063" id="ERRXQST0063"></a>err:XQST0063</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQDY0064" id="ERRXQDY0064"></a>err:XQDY0064</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the value of the name
expression in a computed processing instruction constructor is
equal to "XML" (in any combination of upper and lower case).</p>
</dd>
<dt><a name="ERRXQST0065" id="ERRXQST0065"></a>err:XQST0065</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if a Prolog contains more than one <a title=
"ordering mode declaration" href="#dt-ordering-mode-decl">ordering
mode declaration</a>.</p>
</dd>
<dt><a name="ERRXQST0066" id="ERRXQST0066"></a>err:XQST0066</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if a Prolog contains more than one default
element/type namespace declaration, or more than one default
function namespace declaration.</p>
</dd>
<dt><a name="ERRXQST0067" id="ERRXQST0067"></a>err:XQST0067</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if a Prolog contains more than one <a title=
"construction declaration" href=
"#dt-construction-decl">construction declaration</a>.</p>
</dd>
<dt><a name="ERRXQST0068" id="ERRXQST0068"></a>err:XQST0068</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if a Prolog contains more than one <a title=
"boundary-space declaration" href=
"#dt-boundary-space-decl">boundary-space declaration</a>.</p>
</dd>
<dt><a name="ERRXQST0069" id="ERRXQST0069"></a>err:XQST0069</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if a Prolog contains more than one <a title=
"empty order declaration" href="#dt-empty-order-decl">empty order
declaration</a>.</p>
</dd>
<dt><a name="ERRXQST0070" id="ERRXQST0070"></a>err:XQST0070</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if one of the predefined prefixes
<code>xml</code> or <code>xmlns</code> appears in a namespace
declaration, or if any of the following conditions is statically
detected in any expression or declaration:</p>
<ul>
<li>
<p>The prefix <code>xml</code> is bound to some namespace URI other
than <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>A prefix other than <code>xml</code> is bound to the namespace
URI <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>The prefix <code>xmlns</code> is bound to any namespace URI.</p>
</li>
<li>
<p>A prefix other than <code>xmlns</code> is bound to the namespace
URI <code>http://www.w3.org/2000/xmlns/</code>.</p>
</li>
</ul>
</dd>
<dt><a name="ERRXQST0071" id="ERRXQST0071"></a>err:XQST0071</dt>
<dd>
<p>A <a title="static error" href="#dt-static-error">static
error</a> is raised if the namespace declaration attributes of a
direct element constructor do not have distinct names.</p>
</dd>
<dt><a name="ERRXQDY0072" id="ERRXQDY0072"></a>err:XQDY0072</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the result of the content
expression of a computed comment constructor contains two adjacent
hyphens or ends with a hyphen.</p>
</dd>
<dt><a name="ERRXQST0073" id="ERRXQST0073"></a>err:XQST0073</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQDY0074" id="ERRXQDY0074"></a>err:XQDY0074</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the value of the name
expression in a computed element or attribute constructor cannot be
converted to an <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (for example, because it
contains a namespace prefix not found in <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>.)</p>
</dd>
<dt><a name="ERRXQST0075" id="ERRXQST0075"></a>err:XQST0075</dt>
<dd>
<p>An implementation that does not support the Validation Feature
must raise a <a title="static error" href="#dt-static-error">static
error</a> if it encounters a <code>validate</code> expression.</p>
</dd>
<dt><a name="ERRXQST0076" id="ERRXQST0076"></a>err:XQST0076</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a <code>collation</code> subclause in an <code>order
by</code> clause of a FLWOR expression does not identify a
collation that is present in <a title="statically known collations"
href="#dt-static-collations">statically known collations</a>.</p>
</dd>
<dt><a name="ERRXQST0077" id="ERRXQST0077"></a>err:XQST0077</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0078" id="ERRXQST0078"></a>err:XQST0078</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQST0079" id="ERRXQST0079"></a>err:XQST0079</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if an extension expression contains neither a <a title=
"pragma" href="#dt-pragma">pragma</a> that is recognized by the
implementation nor an expression enclosed in curly braces.</p>
</dd>
<dt><a name="ERRXPST0080" id="ERRXPST0080"></a>err:XPST0080</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the target type of a <code>cast</code> or
<code>castable</code> expression is <code>xs:NOTATION</code> or
<code>xs:anyAtomicType</code>.</p>
</dd>
<dt><a name="ERRXPST0081" id="ERRXPST0081"></a>err:XPST0081</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a QName used in <span class="xquery"><span class=
"xquery">a query</span></span> contains a namespace prefix that
cannot be expanded into a namespace URI by using the <a title=
"statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>.</p>
</dd>
<dt><a name="ERRXQST0082" id="ERRXQST0082"></a>err:XQST0082</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXPST0083" id="ERRXPST0083"></a>err:XPST0083</dt>
<dd>
<p>(Not currently used.)</p>
</dd>
<dt><a name="ERRXQDY0084" id="ERRXQDY0084"></a>err:XQDY0084</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> if the element validated by a
<code>validate</code> statement does not have a top-level element
declaration in the <a title="in-scope element declarations" href=
"#dt-is-elems">in-scope element declarations</a>, if validation
mode is <code>strict</code>.</p>
</dd>
<dt><a name="ERRXQST0085" id="ERRXQST0085"></a>err:XQST0085</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the namespace URI in a namespace declaration attribute
is a zero-length string, and the implementation does not support
<a href="#XMLNAMES11">[XML Names 1.1]</a>.</p>
</dd>
<dt><a name="ERRXQTY0086" id="ERRXQTY0086"></a>err:XQTY0086</dt>
<dd>
<p>It is a <a title="type error" href="#dt-type-error">type
error</a> if the typed value of a copied element or attribute node
is <a title="namespace-sensitive" href=
"#dt-namespace-sensitive">namespace-sensitive</a> when <a title=
"construction mode" href="#dt-construction-mode">construction
mode</a> is <code>preserve</code> and <a title=
"copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> is
<code>no-preserve</code>.</p>
</dd>
<dt><a name="ERRXQST0087" id="ERRXQST0087"></a>err:XQST0087</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the encoding specified in a Version Declaration does
not conform to the definition of <code>EncName</code> specified in
<a href="#XML">[XML 1.0]</a>.</p>
</dd>
<dt><a name="ERRXQST0088" id="ERRXQST0088"></a>err:XQST0088</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if the literal that specifies the target namespace in a
<a title="module import" href="#dt-module-import">module import</a>
or a <a title="module declaration" href=
"#dt-module-declaration">module declaration</a> is of zero
length.</p>
</dd>
<dt><a name="ERRXQST0089" id="ERRXQST0089"></a>err:XQST0089</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a variable bound in a for clause of a FLWOR
expression, and its associated positional variable, do not have
distinct names (expanded QNames).</p>
</dd>
<dt><a name="ERRXQST0090" id="ERRXQST0090"></a>err:XQST0090</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> if a <a title="character reference" href=
"#dt-character-reference">character reference</a> does not identify
a valid character in the version of XML that is in use.</p>
</dd>
<dt><a name="ERRXQDY0091" id="ERRXQDY0091"></a>err:XQDY0091</dt>
<dd>
<p>An implementation <a title="may" href="#may">MAY</a> raise a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
if an <code>xml:id</code> error, as defined in <a href=
"#XMLID">[XML ID]</a>, is encountered during construction of an
attribute named <code>xml:id</code>.</p>
</dd>
<dt><a name="ERRXQDY0092" id="ERRXQDY0092"></a>err:XQDY0092</dt>
<dd>
<p>An implementation <a title="may" href="#may">MAY</a> raise a
<a title="dynamic error" href="#dt-dynamic-error">dynamic error</a>
if a constructed attribute named <code>xml:space</code> has a value
other than <code>preserve</code> or <code>default</code>.</p>
</dd>
<dt><a name="ERRXQST0093" id="ERRXQST0093"></a>err:XQST0093</dt>
<dd>
<p>It is a <a title="static error" href="#dt-static-error">static
error</a> to import a module M<sub>1</sub> if there exists a
sequence of modules M<sub>1</sub> ... M<sub>i</sub> ...
M<sub>1</sub> such that each module <a title=
"module directly depends" href=
"#dt-module-directly-depends">directly depends</a> on the next
module in the sequence (informally, if M<sub>1</sub> depends on
itself through some chain of module dependencies.)</p>
</dd>
<dt><a name="ERRXQDY0096" id="ERRXQDY0096"></a>err:XQDY0096</dt>
<dd>
<p>It is a <a title="dynamic error" href=
"#dt-dynamic-error">dynamic error</a> the node-name of a node
constructed by a computed element constructor has any of the
following properties:</p>
<ul>
<li>
<p>Its namespace prefix is <code>xmlns</code>.</p>
</li>
<li>
<p>Its namespace URI is
<code>http://www.w3.org/2000/xmlns/</code>.</p>
</li>
<li>
<p>Its namespace prefix is <code>xml</code> and its namespace URI
is not <code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
<li>
<p>Its namespace prefix is other than <code>xml</code> and its
namespace URI is
<code>http://www.w3.org/XML/1998/namespace</code>.</p>
</li>
</ul>
</dd>
</dl>
</div>
<div class="xquery">
<div class="div1">
<h2><a name="id-mime-type" id="id-mime-type"></a>G The
<code>application/xquery</code> Media Type</h2>
<p>This Appendix specifies the media type for XQuery Version 1.0.
XQuery is a language for querying over collections of data from XML
data sources, as specified in the main body of this document. This
media type is being submitted to the IESG (Internet Engineering
Steering Group) for review, approval, and registration with IANA
(Internet Assigned Numbers Authority.)</p>
<div class="div2">
<h3><a name="id-mime-type-intro" id="id-mime-type-intro"></a>G.1
Introduction</h3>
<p>This document, found at <span class="xquery"><a href=
"http://www.w3.org/TR/xquery/">http://www.w3.org/TR/xquery/</a></span>,
together with its normative references, defines the language XQuery
Version 1.0. This Appendix provides information about the
<code>application/xquery</code> media type, which is intended to be
used for transmitting queries written in the XQuery language.</p>
<p>This document was prepared by members of the W3C XML Query
Working Group. Please send comments to public-qt-comments@w3.org, a
public mailing list with archives at <a href=
"http://lists.w3.org/Archives/Public/public-qt-comments">http://lists.w3.org/Archives/Public/public-qt-comments</a>.</p>
</div>
<div class="div2">
<h3><a name="id-registration-of-mime-type" id=
"id-registration-of-mime-type"></a>G.2 Registration of MIME Media
Type <code>application/xquery</code></h3>
<p>MIME media type name: <code>application</code></p>
<p>MIME subtype name: <code>xquery</code></p>
<p>Required parameters: none</p>
<p>Optional parameters: none</p>
<p>The syntax of XQuery is expressed in Unicode but may be written
with any Unicode-compatible character encoding, including UTF-8 or
UTF-16, or transported as US-ASCII with Unicode characters outside
the range of the given encoding represented using an XML-style
<code>&amp;#xddd;</code> syntax.</p>
<div class="div3">
<h4><a name="id-interoperability-considerations" id=
"id-interoperability-considerations"></a>G.2.1 Interoperability
Considerations</h4>
<p>None known.</p>
</div>
<div class="div3">
<h4><a name="id-published-specification" id=
"id-published-specification"></a>G.2.2 Published specification</h4>
<p>This media type registration is for XQuery queries as described
by the XQuery 1.0 specification, which is located at <a href=
"http://www.w3.org/TR/xquery/">http://www.w3.org/TR/xquery/</a>. It
is also appropriate to use this media type with later versions of
the XQuery language.</p>
</div>
<div class="div3">
<h4><a name="id-applications-of-media-type" id=
"id-applications-of-media-type"></a>G.2.3 Applications Using this
Media Type</h4>
<p>The public <a href="http://www.w3.org/XML/Query/">XQuery Web
page</a> lists more than two dozen implementations of the XQuery
language, both proprietary and open source.</p>
<p>This new media type is being registered to allow for deployment
of XQuery on the World Wide Web.</p>
</div>
<div class="div3">
<h4><a name="id-file-extensions" id="id-file-extensions"></a>G.2.4
File Extensions</h4>
<p>The most common file extensions in use for XQuery are
<code>.xq</code> and <code>.xquery</code>.</p>
<p>The appropriate Macintosh file type code is
<code>TEXT</code>.</p>
</div>
<div class="div3">
<h4><a name="id-intended-usage" id="id-intended-usage"></a>G.2.5
Intended Usage</h4>
<p>COMMON</p>
</div>
<div class="div3">
<h4><a name="id-author-change-controller" id=
"id-author-change-controller"></a>G.2.6 Author/Change
Controller</h4>
<p>XQuery was produced by, and is maintained by, the World Wide Web
Consortium's XML Query Working Group. The W3C has change control
over this specification.</p>
</div>
</div>
<div class="div2">
<h3><a name="xquery-mime-encoding" id=
"xquery-mime-encoding"></a>G.3 Encoding Considerations</h3>
<p>For use with transports that are not 8-bit clean,
quoted-printable encoding is recommended since the XQuery syntax
itself uses the US-ASCII-compatible subset of Unicode.</p>
<p>An XQuery document may contain an <a title=
"encoding declaration" href="#dt-encoding-declaration">encoding
declaration</a> as part of its <a title="version declaration" href=
"#dt-version-declaration">version declaration</a>:</p>
<div class="exampleInner">
<pre>
xquery version "1.0" encoding "utf-8";
</pre></div>
</div>
<div class="div2">
<h3><a name="xquery-mime-recognizing" id=
"xquery-mime-recognizing"></a>G.4 Recognizing XQuery Files</h3>
<p>An XQuery file may have the string <code>xquery version
"V.V"</code> near the beginning of the document, where
<code>"V.V"</code> is a version number. Currently the version
number, if present, must be <code>"1.0"</code>.</p>
</div>
<div class="div2">
<h3><a name="id-charset-default-rules" id=
"id-charset-default-rules"></a>G.5 Charset Default Rules</h3>
<p>XQuery documents use the Unicode character set and, by default,
the UTF-8 encoding.</p>
</div>
<div class="div2">
<h3><a name="id-security-considerations" id=
"id-security-considerations"></a>G.6 Security Considerations</h3>
<p>Queries written in XQuery may cause arbitrary URIs or IRIs to be
dereferenced. Therefore, the security issues of <a href=
"#RFC3987">[RFC3987]</a> Section 8 should be considered. In
addition, the contents of resources identified by
<code>file:</code> URIs can in some cases be accessed, processed
and returned as results. XQuery expressions can invoke any of the
functions defined in <a href="#FunctionsAndOperators">[XQuery 1.0
and XPath 2.0 Functions and Operators (Second Edition)]</a>. For
example, the <code>fn:doc()</code> and
<code>fn:doc-available()</code> functions allow local filesystem
probes as well as access to any URI-defined resource accessible
from the system evaluating the XQuery expression.</p>
<p>XQuery is a full declarative programming language, and supports
user-defined functions, external function libraries (modules)
referenced by URI, and system-specific "native" functions.</p>
<p>Arbitrary recursion is possible, as is arbitrarily large memory
usage, and implementations may place limits on CPU and memory
usage, as well as restricting access to system-defined
functions.</p>
<p>The XML Query Working group is working on a facility to allow
XQuery expressions to create and update persistent data. Untrusted
queries should not be given write access to data.</p>
<p>Furthermore, because the XQuery language permits extensions, it
is possible that <code>application/xquery</code> may describe
content that has security implications beyond those described
here.</p>
</div>
</div>
</div>
<div class="div1">
<h2><a name="id-glossary" id="id-glossary"></a>H Glossary
(Non-Normative)</h2>
<dl>
<dt><a name="GLdt-full-axis-feature" id=
"GLdt-full-axis-feature"></a>Full Axis Feature</dt>
<dd>
<p>A conforming XQuery implementation that supports the <b>Full
Axis Feature</b> <a title="must" href="#must">MUST</a> support all
the <a title="optional axis" href="#dt-optional-axis">optional
axes</a>.</p>
</dd>
<dt><a name="GLdt-gregorian" id="GLdt-gregorian"></a>Gregorian</dt>
<dd>
<p>In the operator mapping tables, the term <b>Gregorian</b> refers
to the types <code>xs:gYearMonth</code>, <code>xs:gYear</code>,
<code>xs:gMonthDay</code>, <code>xs:gDay</code>, and
<code>xs:gMonth</code>.</p>
</dd>
<dt><a name="GLdt-prolog" id="GLdt-prolog"></a>Prolog</dt>
<dd>
<p>A <b>Prolog</b> is a series of declarations and imports that
define the processing environment for the <a title="module" href=
"#dt-module">module</a> that contains the Prolog.</p>
</dd>
<dt><a name="GLdt-qname" id="GLdt-qname"></a>QName</dt>
<dd>
<p>Lexically, a <b>QName</b> consists of an optional namespace
prefix and a local name. If the namespace prefix is present, it is
separated from the local name by a colon.</p>
</dd>
<dt><a name="GLdt-sequencetype-matching" id=
"GLdt-sequencetype-matching"></a>SequenceType matching</dt>
<dd>
<p>During evaluation of an expression, it is sometimes necessary to
determine whether a value with a known <a title="dynamic type"
href="#dt-dynamic-type">dynamic type</a> "matches" an expected
<a title="sequence type" href="#dt-sequence-type">sequence
type</a>. This process is known as <b>SequenceType
matching</b>.</p>
</dd>
<dt><a name="GLdt-URI" id="GLdt-URI"></a>URI</dt>
<dd>
<p>Within this specification, the term <b>URI</b> refers to a
Universal Resource Identifier as defined in <a href=
"#RFC3986">[RFC3986]</a> and extended in <a href=
"#RFC3987">[RFC3987]</a> with the new name <b>IRI</b>.</p>
</dd>
<dt><a name="GLdt-data-model-instance" id=
"GLdt-data-model-instance"></a>XDM instance</dt>
<dd>
<p>The term <b>XDM instance</b> is used, synonymously with the term
<b>value</b>, to denote an unconstrained sequence of <a title=
"node" href="#dt-node">nodes</a> and/or <a title="atomic value"
href="#dt-atomic-value">atomic values</a> in the <a title=
"data model" href="#dt-datamodel">data model</a>.</p>
</dd>
<dt><a name="GLdt-xpath-compat-mode" id=
"GLdt-xpath-compat-mode"></a>XPath 1.0 compatibility mode</dt>
<dd>
<p><b>XPath 1.0 compatibility mode.</b> <span class=
"xquery"><span class="xquery">This component must be set by all
host languages that include XPath 2.0 as a subset, indicating
whether rules for compatibility with XPath 1.0 are in effect.
XQuery sets the value of this component to
<code>false</code>.</span></span></p>
</dd>
<dt><a name="GLdt-atomic-value" id="GLdt-atomic-value"></a>atomic
value</dt>
<dd>
<p>An <b>atomic value</b> is a value in the value space of an
<b>atomic type</b>, as defined in <a href="#XMLSchema">[XML
Schema]</a>.</p>
</dd>
<dt><a name="GLdt-atomization" id=
"GLdt-atomization"></a>atomization</dt>
<dd>
<p><b>Atomization</b> of a sequence is defined as the result of
invoking the <code>fn:data</code> function on the sequence, as
defined in <a href="#FunctionsAndOperators">[XQuery 1.0 and XPath
2.0 Functions and Operators (Second Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-available-collections" id=
"GLdt-available-collections"></a>available collections</dt>
<dd>
<p><b>Available collections.</b> This is a mapping of strings onto
sequences of nodes. The string represents the absolute URI of a
resource. The sequence of nodes represents the result of the
<code>fn:collection</code> function when that URI is supplied as
the argument.</p>
</dd>
<dt><a name="GLdt-available-docs" id=
"GLdt-available-docs"></a>available documents</dt>
<dd>
<p><b>Available documents.</b> This is a mapping of strings onto
document nodes. The string represents the absolute URI of a
resource. The document node is the root of a tree that represents
that resource using the <a title="data model" href=
"#dt-datamodel">data model</a>. The document node is returned by
the <code>fn:doc</code> function when applied to that URI.</p>
</dd>
<dt><a name="GLdt-axis-step" id="GLdt-axis-step"></a>axis step</dt>
<dd>
<p>An <b>axis step</b> returns a sequence of nodes that are
reachable from the context node via a specified axis. Such a step
has two parts: an <b>axis</b>, which defines the "direction of
movement" for the step, and a <a title="node test" href=
"#dt-node-test">node test</a>, which selects nodes based on their
kind, name, and/or <a title="type annotation" href=
"#dt-type-annotation">type annotation</a>.</p>
</dd>
<dt><a name="GLdt-base-uri" id="GLdt-base-uri"></a>base URI</dt>
<dd>
<p><b>Base URI.</b> This is an absolute URI, used when necessary in
the resolution of relative URIs (for example, by the
<code>fn:resolve-uri</code> function.)</p>
</dd>
<dt><a name="GLdt-base-uri-decl" id="GLdt-base-uri-decl"></a>base
URI declaration</dt>
<dd>
<p>A <b>base URI declaration</b> specifies the <a title="base URI"
href="#dt-base-uri">base URI</a> property of the <a title=
"static context" href="#dt-static-context">static context</a>. The
<a title="base URI" href="#dt-base-uri">base URI</a> property is
used when resolving relative URIs within a <a title="module" href=
"#dt-module">module</a>.</p>
</dd>
<dt><a name="GLdt-binding-sequence" id=
"GLdt-binding-sequence"></a>binding sequence</dt>
<dd>
<p>The value of the expression associated with a variable in a
<code>for</code> clause is called the <b>binding sequence</b> for
that variable.</p>
</dd>
<dt><a name="GLdt-boundary-whitespace" id=
"GLdt-boundary-whitespace"></a>boundary whitespace</dt>
<dd>
<p><b>Boundary whitespace</b> is a sequence of consecutive
whitespace characters within the content of a <a title=
"direct element constructor" href="#dt-direct-elem-const">direct
element constructor</a>, that is delimited at each end either by
the start or end of the content, or by a <a href=
"#doc-xquery-DirectConstructor">DirectConstructor</a>, or by an
<a href="#doc-xquery-EnclosedExpr">EnclosedExpr</a>. For this
purpose, characters generated by <a title="character reference"
href="#dt-character-reference">character references</a> such as
<code>&amp;#x20;</code> or by <a href=
"#doc-xquery-CDataSection">CdataSections</a> are not considered to
be whitespace characters.</p>
</dd>
<dt><a name="GLdt-boundary-space-decl" id=
"GLdt-boundary-space-decl"></a>boundary-space declaration</dt>
<dd>
<p>A <b>boundary-space declaration</b> sets the <a title=
"boundary-space policy" href=
"#dt-boundary-space-policy">boundary-space policy</a> in the
<a title="static context" href="#dt-static-context">static
context</a>, overriding any implementation-defined default.
Boundary-space policy controls whether <a title=
"boundary whitespace" href="#dt-boundary-whitespace">boundary
whitespace</a> is preserved by element constructors during
processing of the query.</p>
</dd>
<dt><a name="GLdt-boundary-space-policy" id=
"GLdt-boundary-space-policy"></a>boundary-space policy</dt>
<dd>
<p><b>Boundary-space policy.</b> This component controls the
processing of <a title="boundary whitespace" href=
"#dt-boundary-whitespace">boundary whitespace</a> by <a title=
"direct element constructor" href="#dt-direct-elem-const">direct
element constructors</a>, as described in <a href=
"#id-whitespace"><b>3.7.1.4 Boundary Whitespace</b></a>.</p>
</dd>
<dt><a name="GLdt-built-in-function" id=
"GLdt-built-in-function"></a>built-in function</dt>
<dd>
<p>The <b>built-in functions</b> supported by XQuery are defined in
<a href="#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0
Functions and Operators (Second Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-character-reference" id=
"GLdt-character-reference"></a>character reference</dt>
<dd>
<p>A <b>character reference</b> is an XML-style reference to a
<a href="#Unicode">[Unicode]</a> character, identified by its
decimal or hexadecimal code point.</p>
</dd>
<dt><a name="GLdt-collation" id="GLdt-collation"></a>collation</dt>
<dd>
<p>A <b>collation</b> is a specification of the manner in which
strings and URIs are compared and, by extension, ordered. For a
more complete definition of collation, see <a href=
"#FunctionsAndOperators">[XQuery 1.0 and XPath 2.0 Functions and
Operators (Second Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-comma-operator" id=
"GLdt-comma-operator"></a>comma operator</dt>
<dd>
<p>One way to construct a sequence is by using the <b>comma
operator</b>, which evaluates each of its operands and concatenates
the resulting sequences, in order, into a single result
sequence.</p>
</dd>
<dt><a name="GLdt-computed-elem-const" id=
"GLdt-computed-elem-const"></a>computed element constructor</dt>
<dd>
<p>A <b>computed element constructor</b> creates an element node,
allowing both the name and the content of the node to be
computed.</p>
</dd>
<dt><a name="GLdt-construction-decl" id=
"GLdt-construction-decl"></a>construction declaration</dt>
<dd>
<p>A <b>construction declaration</b> sets the <a title=
"construction mode" href="#dt-construction-mode">construction
mode</a> in the <a title="static context" href=
"#dt-static-context">static context</a>, overriding any
implementation-defined default.</p>
</dd>
<dt><a name="GLdt-construction-mode" id=
"GLdt-construction-mode"></a>construction mode</dt>
<dd>
<p><b>Construction mode.</b> The construction mode governs the
behavior of element and document node constructors. If construction
mode is <code>preserve</code>, the type of a constructed element
node is <code>xs:anyType</code>, and all attribute and element
nodes copied during node construction retain their original types.
If construction mode is <code>strip</code>, the type of a
constructed element node is <code>xs:untyped</code>; all element
nodes copied during node construction receive the type
<code>xs:untyped</code>, and all attribute nodes copied during node
construction receive the type <code>xs:untypedAtomic</code>.</p>
</dd>
<dt><a name="GLdt-constructor-function" id=
"GLdt-constructor-function"></a>constructor function</dt>
<dd>
<p>The <b>constructor function</b> for a given type is used to
convert instances of other atomic types into the given type. The
semantics of the constructor function call <code>T($arg)</code> are
defined to be equivalent to the expression <code>(($arg) cast as
T?)</code>.</p>
</dd>
<dt><a name="GLdt-content-expression" id=
"GLdt-content-expression"></a>content expression</dt>
<dd>
<p>The final part of a computed constructor is an expression
enclosed in braces, called the <b>content expression</b> of the
constructor, that generates the content of the node.</p>
</dd>
<dt><a name="GLdt-context-item" id="GLdt-context-item"></a>context
item</dt>
<dd>
<p>The <b>context item</b> is the item currently being processed.
An item is either an atomic value or a node.</p>
</dd>
<dt><a name="GLdt-context-item-static-type" id=
"GLdt-context-item-static-type"></a>context item static type</dt>
<dd>
<p><b>Context item static type.</b> This component defines the
<a title="static type" href="#dt-static-type">static type</a> of
the context item within the scope of a given expression.</p>
</dd>
<dt><a name="GLdt-context-node" id="GLdt-context-node"></a>context
node</dt>
<dd>
<p>When the context item is a node, it can also be referred to as
the <b>context node</b>.</p>
</dd>
<dt><a name="GLdt-context-position" id=
"GLdt-context-position"></a>context position</dt>
<dd>
<p>The <b>context position</b> is the position of the context item
within the sequence of items currently being processed.</p>
</dd>
<dt><a name="GLdt-context-size" id="GLdt-context-size"></a>context
size</dt>
<dd>
<p>The <b>context size</b> is the number of items in the sequence
of items currently being processed.</p>
</dd>
<dt><a name="GLdt-copy-namespaces-decl" id=
"GLdt-copy-namespaces-decl"></a>copy-namespaces declaration</dt>
<dd>
<p>A <b>copy-namespaces declaration</b> sets the value of <a title=
"copy-namespaces mode" href=
"#dt-copy-namespaces-mode">copy-namespaces mode</a> in the
<a title="static context" href="#dt-static-context">static
context</a>, overriding any implementation-defined default.
Copy-namespaces mode controls the namespace bindings that are
assigned when an existing element node is copied by an element
constructor or document constructor.</p>
</dd>
<dt><a name="GLdt-copy-namespaces-mode" id=
"GLdt-copy-namespaces-mode"></a>copy-namespaces mode</dt>
<dd>
<p><b>Copy-namespaces mode.</b> This component controls the
namespace bindings that are assigned when an existing element node
is copied by an element constructor, as described in <a href=
"#id-element-constructor"><b>3.7.1 Direct Element
Constructors</b></a>. Its value consists of two parts:
<code>preserve</code> or <code>no-preserve</code>, and
<code>inherit</code> or <code>no-inherit</code>.</p>
</dd>
<dt><a name="GLdt-date-time" id="GLdt-date-time"></a>current
dateTime</dt>
<dd>
<p><b>Current dateTime.</b> This information represents an
<a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> point
in time during the processing of <span class="xquery"><span class=
"xquery">a query</span></span>, and includes an explicit timezone.
It can be retrieved by the <code>fn:current-dateTime</code>
function. If invoked multiple times during the execution of
<span class="xquery"><span class="xquery">a query</span></span>,
this function always returns the same result.</p>
</dd>
<dt><a name="GLdt-datamodel" id="GLdt-datamodel"></a>data
model</dt>
<dd>
<p>XQuery operates on the abstract, logical structure of an XML
document, rather than its surface syntax. This logical structure,
known as the <b>data model</b>, is defined in <a href=
"#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-data-model-schema" id=
"GLdt-data-model-schema"></a>data model schema</dt>
<dd>
<p>For a given node in an <a title="XDM instance" href=
"#dt-data-model-instance">XDM instance</a>, the <b>data model
schema</b> is defined as the schema from which the <a title=
"type annotation" href="#dt-type-annotation">type annotation</a> of
that node was derived.</p>
</dd>
<dt><a name="GLdt-def-collation" id=
"GLdt-def-collation"></a>default collation</dt>
<dd>
<p><b>Default collation.</b> This identifies one of the collations
in <a title="statically known collations" href=
"#dt-static-collations">statically known collations</a> as the
collation to be used by functions and operators for comparing and
ordering values of type <code>xs:string</code> and
<code>xs:anyURI</code> (and types derived from them) when no
explicit collation is specified.</p>
</dd>
<dt><a name="GLdt-default-collation-decl" id=
"GLdt-default-collation-decl"></a>default collation
declaration</dt>
<dd>
<p>A <b>default collation declaration</b> sets the value of the
<a title="default collation" href="#dt-def-collation">default
collation</a> in the <a title="static context" href=
"#dt-static-context">static context</a>, overriding any
implementation-defined default.</p>
</dd>
<dt><a name="GLdt-default-collection" id=
"GLdt-default-collection"></a>default collection</dt>
<dd>
<p><b>Default collection.</b> This is the sequence of nodes that
would result from calling the <code>fn:collection</code> function
with no arguments.</p>
</dd>
<dt><a name="GLdt-def-elemtype-ns" id=
"GLdt-def-elemtype-ns"></a>default element/type namespace</dt>
<dd>
<p><b>Default element/type namespace.</b> This is a namespace URI
or "none". The namespace URI, if present, is used for any
unprefixed QName appearing in a position where an element or type
name is expected.</p>
</dd>
<dt><a name="GLdt-def-fn-ns" id="GLdt-def-fn-ns"></a>default
function namespace</dt>
<dd>
<p><b>Default function namespace.</b> This is a namespace URI or
"none". The namespace URI, if present, is used for any unprefixed
QName appearing in a position where a function name is
expected.</p>
</dd>
<dt><a name="GLdt-default-empty-order" id=
"GLdt-default-empty-order"></a>default order for empty
sequences</dt>
<dd>
<p><b>Default order for empty sequences.</b> This component
controls the processing of empty sequences and <code>NaN</code>
values as ordering keys in an <code>order by</code> clause in a
FLWOR expression, as described in <a href=
"#id-orderby-return"><b>3.8.3 Order By and Return
Clauses</b></a>.</p>
</dd>
<dt><a name="GLdelimiting-token" id=
"GLdelimiting-token"></a>delimiting terminal symbol</dt>
<dd>
<p>The <b>delimiting terminal symbols</b> are: <a href=
"#prod-xquery-S">S</a>, "!=", <a href=
"#prod-xquery-StringLiteral">StringLiteral</a>, "#)", "$", "(",
"(#", ")", "*", "+", (comma), "-", "--&gt;", (dot), "..", "/",
"//", "/&gt;", (colon), "::", ":=", (semi-colon), "&lt;",
"&lt;!--", "&lt;![CDATA[", "&lt;/", "&lt;&lt;", "&lt;=", "&lt;?",
"=", "&gt;", "&gt;=", "&gt;&gt;", "?", "?&gt;", "@", "[", "]",
"]]&gt;", "{", "|", "}"</p>
</dd>
<dt><a name="GLdt-direct-elem-const" id=
"GLdt-direct-elem-const"></a>direct element constructor</dt>
<dd>
<p>A <b>direct element constructor</b> is a form of element
constructor in which the name of the constructed element is a
constant.</p>
</dd>
<dt><a name="GLdt-document-order" id=
"GLdt-document-order"></a>document order</dt>
<dd>
<p>Informally, <b>document order</b> is the order in which nodes
appear in the XML serialization of a document.</p>
</dd>
<dt><a name="GLdt-dynamic-context" id=
"GLdt-dynamic-context"></a>dynamic context</dt>
<dd>
<p>The <b>dynamic context</b> of an expression is defined as
information that is available at the time the expression is
evaluated.</p>
</dd>
<dt><a name="GLdt-dynamic-error" id=
"GLdt-dynamic-error"></a>dynamic error</dt>
<dd>
<p>A <b>dynamic error</b> is an error that must be detected during
the dynamic evaluation phase and may be detected during the static
analysis phase. Numeric overflow is an example of a dynamic
error.</p>
</dd>
<dt><a name="GLdt-dynamic-evaluation" id=
"GLdt-dynamic-evaluation"></a>dynamic evaluation phase</dt>
<dd>
<p>The <b>dynamic evaluation phase</b> is the phase during which
the value of an expression is computed.</p>
</dd>
<dt><a name="GLdt-dynamic-type" id="GLdt-dynamic-type"></a>dynamic
type</dt>
<dd>
<p>A <b>dynamic type</b> is associated with each value as it is
computed. The dynamic type of a value may be more specific than the
<a title="static type" href="#dt-static-type">static type</a> of
the expression that computed it (for example, the static type of an
expression might be <code>xs:integer*</code>, denoting a sequence
of zero or more integers, but at evaluation time its value may have
the dynamic type <code>xs:integer</code>, denoting exactly one
integer.)</p>
</dd>
<dt><a name="GLdt-ebv" id="GLdt-ebv"></a>effective boolean
value</dt>
<dd>
<p>The <b>effective boolean value</b> of a value is defined as the
result of applying the <code>fn:boolean</code> function to the
value, as defined in <a href="#FunctionsAndOperators">[XQuery 1.0
and XPath 2.0 Functions and Operators (Second Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-effective-case" id=
"GLdt-effective-case"></a>effective case</dt>
<dd>
<p>The <b>effective case</b> in a <code>typeswitch</code>
expression is the first <code>case</code> clause such that the
value of the operand expression matches the <a href=
"#doc-xquery-SequenceType">SequenceType</a> in the
<code>case</code> clause, using the rules of <a title=
"SequenceType matching" href=
"#dt-sequencetype-matching">SequenceType matching</a>.</p>
</dd>
<dt><a name="GLdt-empty-order-decl" id=
"GLdt-empty-order-decl"></a>empty order declaration</dt>
<dd>
<p>An <b>empty order declaration</b> sets the <a title=
"default order for empty sequences" href=
"#dt-default-empty-order">default order for empty sequences</a> in
the <a title="static context" href="#dt-static-context">static
context,</a> overriding any implementation-defined default. This
declaration controls the processing of empty sequences and
<code>NaN</code> values as ordering keys in an <code>order
by</code> clause in a FLWOR expression.</p>
</dd>
<dt><a name="GLdt-empty-sequence" id=
"GLdt-empty-sequence"></a>empty sequence</dt>
<dd>
<p>A sequence containing zero items is called an <b>empty
sequence</b>.</p>
</dd>
<dt><a name="GLdt-encoding-declaration" id=
"GLdt-encoding-declaration"></a>encoding declaration</dt>
<dd>
<p>If present, a version declaration may optionally include an
<b>encoding declaration</b>. The value of the string literal
following the keyword <code>encoding</code> is an encoding name,
and must conform to the definition of <code>EncName</code>
specified in <a href="#XML">[XML 1.0]</a>[<a href="#ERRXQST0087"
title="err:XQST0087">err:XQST0087</a>]. The purpose of an encoding
declaration is to allow the writer of a query to provide a string
that indicates how the query is encoded, such as
"<code>UTF-8</code>", "<code>UTF-16</code>", or
"<code>US-ASCII</code>".</p>
</dd>
<dt><a name="GLdt-error-value" id="GLdt-error-value"></a>error
value</dt>
<dd>
<p>In addition to its identifying QName, a dynamic error may also
carry a descriptive string and one or more additional values called
<b>error values</b>.</p>
</dd>
<dt><a name="GLdt-expanded-qname" id=
"GLdt-expanded-qname"></a>expanded QName</dt>
<dd>
<p>An <b>expanded QName</b> consists of an optional namespace URI
and a local name. An expanded QName also retains its original
namespace prefix (if any), to facilitate casting the expanded QName
into a string.</p>
</dd>
<dt><a name="GLdt-expression-context" id=
"GLdt-expression-context"></a>expression context</dt>
<dd>
<p>The <b>expression context</b> for a given expression consists of
all the information that can affect the result of the
expression.</p>
</dd>
<dt><a name="GLdt-extension-expression" id=
"GLdt-extension-expression"></a>extension expression</dt>
<dd>
<p>An <b>extension expression</b> is an expression whose semantics
are <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
</dd>
<dt><a name="GLdt-external-function" id=
"GLdt-external-function"></a>external function</dt>
<dd>
<p><b>External functions</b> are functions that are implemented
outside the query environment.</p>
</dd>
<dt><a name="GLdt-filter-expression" id=
"GLdt-filter-expression"></a>filter expression</dt>
<dd>
<p>A <b>filter expression</b> consists simply of a <b>primary
expression</b> followed by zero or more <a title="predicate" href=
"#dt-predicate">predicates</a>. The result of the filter expression
consists of the items returned by the primary expression, filtered
by applying each predicate in turn, working from left to right.</p>
</dd>
<dt><a name="GLdt-focus" id="GLdt-focus"></a>focus</dt>
<dd>
<p>The first three components of the <a title="dynamic context"
href="#dt-dynamic-context">dynamic context</a> (context item,
context position, and context size) are called the <b>focus</b> of
the expression.</p>
</dd>
<dt><a name="GLdt-function-depends" id=
"GLdt-function-depends"></a>function depends</dt>
<dd>
<p>A function <code>f1</code> <b>depends</b> on a variable
<code>$y</code> or a function <code>f2</code> if a reference to
<code>$y</code> or <code>f2</code> appears in the body of
<code>f1</code>, or if there exists a variable <code>$z</code> or a
function <code>f3</code> such that <code>f1</code> <a title=
"function depends" href="#dt-function-depends">depends</a> on
<code>$z</code> or <code>f3</code> and <code>$z</code> or
<code>f3</code> <a title="variable depends" href=
"#dt-variable-depends">depends</a> on <code>$y</code> or
<code>f2</code>.</p>
</dd>
<dt><a name="GLdt-function-implementation" id=
"GLdt-function-implementation"></a>function implementation</dt>
<dd>
<p><b>Function implementations</b>. Each function in <a title=
"function signature" href="#dt-function-signature">function
signatures</a> has a function implementation that enables the
function to map instances of its parameter types into an instance
of its result type. <span class="xquery"><span class="xquery">For a
<a title="user-defined function" href="#dt-udf">user-defined
function</a>, the function implementation is an XQuery expression.
For a <a title="built-in function" href=
"#dt-built-in-function">built-in function</a> or <a title=
"external function" href="#dt-external-function">external
function</a>, the function implementation is <a title=
"implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</span></span></p>
</dd>
<dt><a name="GLdt-function-signature" id=
"GLdt-function-signature"></a>function signature</dt>
<dd>
<p><b>Function signatures.</b> This component defines the set of
functions that are available to be called from within an
expression. Each function is uniquely identified by its <a title=
"expanded QName" href="#dt-expanded-qname">expanded QName</a> and
its arity (number of parameters).</p>
</dd>
<dt><a name="GLIgnorableWhitespace" id=
"GLIgnorableWhitespace"></a>ignorable whitespace</dt>
<dd>
<p><b>Ignorable whitespace</b> consists of any <a title=
"whitespace" href="#Whitespace">whitespace</a> characters that may
occur between <a title="terminal" href="#terminal">terminals</a>,
unless these characters occur in the context of a production marked
with a <a href="#ExplicitWhitespaceHandling">ws:explicit</a>
annotation, in which case they can occur only where explicitly
specified (see <a href="#ExplicitWhitespaceHandling"><b>A.2.4.2
Explicit Whitespace Handling</b></a>).</p>
</dd>
<dt><a name="GLdt-implementation-dependent" id=
"GLdt-implementation-dependent"></a>implementation dependent</dt>
<dd>
<p><b>Implementation-dependent</b> indicates an aspect that may
differ between implementations, is not specified by this or any W3C
specification, and is not required to be specified by the
implementor for any particular implementation.</p>
</dd>
<dt><a name="GLdt-implementation-defined" id=
"GLdt-implementation-defined"></a>implementation defined</dt>
<dd>
<p><b>Implementation-defined</b> indicates an aspect that may
differ between implementations, but must be specified by the
implementor for each particular implementation.</p>
</dd>
<dt><a name="GLdt-timezone" id="GLdt-timezone"></a>implicit
timezone</dt>
<dd>
<p><b>Implicit timezone.</b> This is the timezone to be used when a
date, time, or dateTime value that does not have a timezone is used
in a comparison or arithmetic operation. The implicit timezone is
an <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> value of
type <code>xs:dayTimeDuration</code>. See <a href="#XMLSchema">[XML
Schema]</a> for the range of legal values of a timezone.</p>
</dd>
<dt><a name="GLdt-is-attrs" id="GLdt-is-attrs"></a>in-scope
attribute declarations</dt>
<dd>
<p><b>In-scope attribute declarations.</b> Each attribute
declaration is identified either by an <a title="expanded QName"
href="#dt-expanded-qname">expanded QName</a> (for a top-level
attribute declaration) or by an <a title="implementation dependent"
href="#dt-implementation-dependent">implementation-dependent</a>
attribute identifier (for a local attribute declaration).
<span class="xquery"><span class="xquery">If the <a title=
"schema import feature" href="#dt-schema-import-feature">Schema
Import Feature</a> is supported, in-scope attribute declarations
include all attribute declarations found in imported
schemas.</span></span></p>
</dd>
<dt><a name="GLdt-is-elems" id="GLdt-is-elems"></a>in-scope element
declarations</dt>
<dd>
<p><b>In-scope element declarations.</b> Each element declaration
is identified either by an <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (for a top-level element
declaration) or by an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> element
identifier (for a local element declaration). <span class=
"xquery"><span class="xquery">If the <a title=
"schema import feature" href="#dt-schema-import-feature">Schema
Import Feature</a> is supported, in-scope element declarations
include all element declarations found in imported
schemas.</span></span></p>
</dd>
<dt><a name="GLdt-in-scope-namespaces" id=
"GLdt-in-scope-namespaces"></a>in-scope namespaces</dt>
<dd>
<p>The <b>in-scope namespaces</b> property of an element node is a
set of <b>namespace bindings</b>, each of which associates a
namespace prefix with a URI, thus defining the set of namespace
prefixes that are available for interpreting QNames within the
scope of the element. For a given element, one namespace binding
may have an empty prefix; the URI of this namespace binding is the
default namespace within the scope of the element.</p>
</dd>
<dt><a name="GLdt-issd" id="GLdt-issd"></a>in-scope schema
definitions</dt>
<dd>
<p><b>In-scope schema definitions.</b> This is a generic term for
all the element declarations, attribute declarations, and schema
type definitions that are in scope during processing of an
expression.</p>
</dd>
<dt><a name="GLdt-is-types" id="GLdt-is-types"></a>in-scope schema
type</dt>
<dd>
<p><b>In-scope schema types.</b> Each schema type definition is
identified either by an <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> (for a <b>named type</b>)
or by an <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a> type
identifier (for an <b>anonymous type</b>). The in-scope schema
types include the predefined schema types described in <a href=
"#id-predefined-types"><b>2.5.1 Predefined Schema Types</b></a>.
<span class="xquery"><span class="xquery">If the <a title=
"schema import feature" href="#dt-schema-import-feature">Schema
Import Feature</a> is supported, in-scope schema types also include
all type definitions found in imported schemas.</span></span></p>
</dd>
<dt><a name="GLdt-in-scope-variables" id=
"GLdt-in-scope-variables"></a>in-scope variables</dt>
<dd>
<p><b>In-scope variables.</b> This is a set of (expanded QName,
type) pairs. It defines the set of variables that are available for
reference within an expression. The <a title="expanded QName" href=
"#dt-expanded-qname">expanded QName</a> is the name of the
variable, and the type is the <a title="static type" href=
"#dt-static-type">static type</a> of the variable.</p>
</dd>
<dt><a name="GLdt-initializing-expression" id=
"GLdt-initializing-expression"></a>initializing expression</dt>
<dd>
<p>If a variable declaration includes an expression, the expression
is called an <b>initializing expression</b>.</p>
</dd>
<dt><a name="GLdt-item" id="GLdt-item"></a>item</dt>
<dd>
<p>An <b>item</b> is either an <a title="atomic value" href=
"#dt-atomic-value">atomic value</a> or a <a title="node" href=
"#dt-node">node</a>.</p>
</dd>
<dt><a name="GLdt-kind-test" id="GLdt-kind-test"></a>kind test</dt>
<dd>
<p>An alternative form of a node test called a <b>kind test</b> can
select nodes based on their kind, name, and <a title=
"type annotation" href="#dt-type-annotation">type
annotation</a>.</p>
</dd>
<dt><a name="GLdt-library-module" id=
"GLdt-library-module"></a>library module</dt>
<dd>
<p>A module that does not contain a <a title="query body" href=
"#dt-queryBody">Query Body</a> is called a <b>library module</b>. A
library module consists of a <a title="module declaration" href=
"#dt-module-declaration">module declaration</a> followed by a
<a title="Prolog" href="#dt-prolog">Prolog</a>.</p>
</dd>
<dt><a name="GLdt-literal" id="GLdt-literal"></a>literal</dt>
<dd>
<p>A <b>literal</b> is a direct syntactic representation of an
atomic value.</p>
</dd>
<dt><a name="GLdt-main-module" id="GLdt-main-module"></a>main
module</dt>
<dd>
<p>A <b>main module</b> consists of a <a title="Prolog" href=
"#dt-prolog">Prolog</a> followed by a <a title="query body" href=
"#dt-queryBody">Query Body</a>.</p>
</dd>
<dt><a name="GLmay" id="GLmay"></a>may</dt>
<dd>
<p><b>MAY</b> means that an item is truly optional.</p>
</dd>
<dt><a name="GLdt-module" id="GLdt-module"></a>module</dt>
<dd>
<p>A <b>module</b> is a fragment of XQuery code that conforms to
the <a href="#doc-xquery-Module">Module</a> grammar and can
independently undergo the <a title="static analysis phase" href=
"#dt-static-analysis">static analysis phase</a> described in
<a href="#id-expression-processing"><b>2.2.3 Expression
Processing</b></a>. Each module is either a <a title="main module"
href="#dt-main-module">main module</a> or a <a title=
"library module" href="#dt-library-module">library module</a>.</p>
</dd>
<dt><a name="GLdt-module-declaration" id=
"GLdt-module-declaration"></a>module declaration</dt>
<dd>
<p>A <b>module declaration</b> serves to identify a <a title=
"module" href="#dt-module">module</a> as a <a title=
"library module" href="#dt-library-module">library module</a>. A
module declaration begins with the keyword <code>module</code> and
contains a namespace prefix and a <a href=
"#doc-xquery-URILiteral">URILiteral</a>.</p>
</dd>
<dt><a name="GLdt-module-directly-depends" id=
"GLdt-module-directly-depends"></a>module directly depends</dt>
<dd>
<p>A module M<sub>1</sub> <b>directly depends</b> on another module
M<sub>2</sub> (different from M<sub>1</sub>) if a variable or
function declared in M<sub>1</sub> <a title="variable depends"
href="#dt-variable-depends">depends</a> on a variable or function
declared in M<sub>2</sub>.</p>
</dd>
<dt><a name="GLdt-module-feature" id=
"GLdt-module-feature"></a>module feature</dt>
<dd>
<p>A conforming XQuery implementation that supports the <b>Module
Feature</b> allows a query Prolog to contain a <b>Module Import</b>
and allows <b>library modules</b> to be created.</p>
</dd>
<dt><a name="GLdt-module-import" id="GLdt-module-import"></a>module
import</dt>
<dd>
<p>A <b>module import</b> imports the function declarations and
variable declarations from one or more <a title="library module"
href="#dt-library-module">library modules</a> into the <a title=
"function signature" href="#dt-function-signature">function
signatures</a> and <a title="in-scope variables" href=
"#dt-in-scope-variables">in-scope variables</a> of the importing
<a title="module" href="#dt-module">module</a>.</p>
</dd>
<dt><a name="GLmust" id="GLmust"></a>must</dt>
<dd>
<p><b>MUST</b> means that the item is an absolute requirement of
the specification.</p>
</dd>
<dt><a name="GLdt-name-expression" id=
"GLdt-name-expression"></a>name expression</dt>
<dd>
<p>When an expression is used to specify the name of a constructed
node, that expression is called the <b>name expression</b> of the
constructor.</p>
</dd>
<dt><a name="GLdt-name-test" id="GLdt-name-test"></a>name test</dt>
<dd>
<p>A node test that consists only of a QName or a Wildcard is
called a <b>name test</b>.</p>
</dd>
<dt><a name="GLdt-namespace-declaration" id=
"GLdt-namespace-declaration"></a>namespace declaration</dt>
<dd>
<p>A <b>namespace declaration</b> declares a namespace prefix and
associates it with a namespace URI, adding the (prefix, URI) pair
to the set of <a title="statically known namespaces" href=
"#dt-static-namespaces">statically known namespaces</a>.</p>
</dd>
<dt><a name="GLdt-namespace-decl-attr" id=
"GLdt-namespace-decl-attr"></a>namespace declaration attribute</dt>
<dd>
<p>A <b>namespace declaration attribute</b> is used inside a direct
element constructor. Its purpose is to bind a namespace prefix or
to set the <a title="default element/type namespace" href=
"#dt-def-elemtype-ns">default element/type namespace</a> for the
constructed element node, including its attributes.</p>
</dd>
<dt><a name="GLdt-namespace-sensitive" id=
"GLdt-namespace-sensitive"></a>namespace-sensitive</dt>
<dd>
<p>A value is <b>namespace-sensitive</b> if it includes an item
whose <a title="dynamic type" href="#dt-dynamic-type">dynamic
type</a> is <code>xs:QName</code> or <code>xs:NOTATION</code> or is
derived by restriction from <code>xs:QName</code> or
<code>xs:NOTATION</code>.</p>
</dd>
<dt><a name="GLdt-node" id="GLdt-node"></a>node</dt>
<dd>
<p>A <b>node</b> is an instance of one of the <b>node kinds</b>
defined in <a href="#datamodel">[XQuery 1.0 and XPath 2.0 Data
Model (Second Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-node-test" id="GLdt-node-test"></a>node test</dt>
<dd>
<p>A <b>node test</b> is a condition that must be true for each
node selected by a <a title="step" href="#dt-step">step</a>.</p>
</dd>
<dt><a name="GLnon-delimiting-token" id=
"GLnon-delimiting-token"></a>non-delimiting terminal symbol</dt>
<dd>
<p>The <b>non-delimiting terminal symbols</b> are: <a href=
"#prod-xquery-IntegerLiteral">IntegerLiteral</a>, <a href=
"#prod-xquery-NCName">NCName</a>, <a href=
"#prod-xquery-DecimalLiteral">DecimalLiteral</a>, <a href=
"#prod-xquery-DoubleLiteral">DoubleLiteral</a>, <a href=
"#prod-xquery-QName">QName</a>, "ancestor", "ancestor-or-self",
"and", "as", "ascending", "at", "attribute", "base-uri",
"boundary-space", "by", "case", "cast", "castable", "child",
"collation", "comment", "construction", "copy-namespaces",
"declare", "default", "descendant", "descendant-or-self",
"descending", "div", "document", "document-node", "element",
"else", "empty", "empty-sequence", "encoding", "eq", "every",
"except", "external", "following", "following-sibling", "for",
"function", "ge", "greatest", "gt", "idiv", "if", "import", "in",
"inherit", "instance", "intersect", "is", "item", "lax", "le",
"least", "let", "lt", "mod", "module", "namespace", "ne",
"no-inherit", "no-preserve", "node", "of", "option", "or", "order",
"ordered", "ordering", "parent", "preceding", "preceding-sibling",
"preserve", "processing-instruction", "return", "satisfies",
"schema", "schema-attribute", "schema-element", "self", "some",
"stable", "strict", "strip", "text", "then", "to", "treat",
"typeswitch", "union", "unordered", "validate", "variable",
"version", "where", "xquery"</p>
</dd>
<dt><a name="GLdt-numeric" id="GLdt-numeric"></a>numeric</dt>
<dd>
<p>When referring to a type, the term <b>numeric</b> denotes the
types <code>xs:integer</code>, <code>xs:decimal</code>,
<code>xs:float</code>, and <code>xs:double</code>.</p>
</dd>
<dt><a name="GLdt-numeric-predicate" id=
"GLdt-numeric-predicate"></a>numeric predicate</dt>
<dd>
<p>A predicate whose predicate expression returns a numeric type is
called a <b>numeric predicate</b>.</p>
</dd>
<dt><a name="GLdt-operator-function" id=
"GLdt-operator-function"></a>operator function</dt>
<dd>
<p>For each operator and valid combination of operand types, the
operator mapping tables specify a result type and an <b>operator
function</b> that implements the semantics of the operator for the
given types.</p>
</dd>
<dt><a name="GLdt-option-declaration" id=
"GLdt-option-declaration"></a>option declaration</dt>
<dd>
<p>An <b>option declaration</b> declares an option that affects the
behavior of a particular implementation. Each option consists of an
identifying QName and a StringLiteral.</p>
</dd>
<dt><a name="GLdt-optional-axis" id=
"GLdt-optional-axis"></a>optional axis</dt>
<dd>
<p>The following axes are designated as <b>optional axes</b>:
<code>ancestor</code>, <code>ancestor-or-self</code>,
<code>following</code>, <code>following-sibling</code>,
<code>preceding</code>, and <code>preceding-sibling</code>.</p>
</dd>
<dt><a name="GLdt-ordering-mode" id=
"GLdt-ordering-mode"></a>ordering mode</dt>
<dd>
<p><b>Ordering mode.</b> Ordering mode, which has the value
<code>ordered</code> or <code>unordered</code>, affects the
ordering of the result sequence returned by certain <a title=
"path expression" href="#dt-path-expression">path expressions</a>,
<code>union</code>, <code>intersect</code>, and <code>except</code>
expressions, and FLWOR expressions that have no <code>order
by</code> clause.</p>
</dd>
<dt><a name="GLdt-ordering-mode-decl" id=
"GLdt-ordering-mode-decl"></a>ordering mode declaration</dt>
<dd>
<p>An <b>ordering mode declaration</b> sets the <a title=
"ordering mode" href="#dt-ordering-mode">ordering mode</a> in the
<a title="static context" href="#dt-static-context">static
context</a>, overriding any implementation-defined default.</p>
</dd>
<dt><a name="GLdt-path-expression" id=
"GLdt-path-expression"></a>path expression</dt>
<dd>
<p>A <b>path expression</b> can be used to locate nodes within
trees. A path expression consists of a series of one or more
<a title="step" href="#dt-step">steps</a>, separated by
"<code>/</code>" or "<code>//</code>", and optionally beginning
with "<code>/</code>" or "<code>//</code>".</p>
</dd>
<dt><a name="GLdt-pragma" id="GLdt-pragma"></a>pragma</dt>
<dd>
<p>A <b>pragma</b> is denoted by the delimiters <code>(#</code> and
<code>#)</code>, and consists of an identifying QName followed by
<a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>
content.</p>
</dd>
<dt><a name="GLdt-predefined-entity-reference" id=
"GLdt-predefined-entity-reference"></a>predefined entity
reference</dt>
<dd>
<p>A <b>predefined entity reference</b> is a short sequence of
characters, beginning with an ampersand, that represents a single
character that might otherwise have syntactic significance.</p>
</dd>
<dt><a name="GLdt-predicate" id="GLdt-predicate"></a>predicate</dt>
<dd>
<p>A <b>predicate</b> consists of an expression, called a
<b>predicate expression</b>, enclosed in square brackets. A
predicate serves to filter a sequence, retaining some items and
discarding others.</p>
</dd>
<dt><a name="GLdt-primary-expression" id=
"GLdt-primary-expression"></a>primary expression</dt>
<dd>
<p><b>Primary expressions</b> are the basic primitives of the
language. They include literals, variable references, context item
expressions, <span class="xquery"><span class=
"xquery">constructors,</span></span> and function calls. A primary
expression may also be created by enclosing any expression in
parentheses, which is sometimes helpful in controlling the
precedence of operators.</p>
</dd>
<dt><a name="GLdt-principal-node-kind" id=
"GLdt-principal-node-kind"></a>principal node kind</dt>
<dd>
<p>Every axis has a <b>principal node kind</b>. If an axis can
contain elements, then the principal node kind is element;
otherwise, it is the kind of nodes that the axis can contain.</p>
</dd>
<dt><a name="GLdt-query" id="GLdt-query"></a>query</dt>
<dd>
<p>A <b>query</b> consists of one or more <a title="module" href=
"#dt-module">modules</a>.</p>
</dd>
<dt><a name="GLdt-queryBody" id="GLdt-queryBody"></a>query
body</dt>
<dd>
<p>The <b>Query Body</b>, if present, consists of an expression
that defines the result of the query.</p>
</dd>
<dt><a name="GLdt-reverse-document-order" id=
"GLdt-reverse-document-order"></a>reverse document order</dt>
<dd>
<p>The node ordering that is the reverse of document order is
called <b>reverse document order</b>.</p>
</dd>
<dt><a name="GLdt-schema-import" id="GLdt-schema-import"></a>schema
import</dt>
<dd>
<p>A <b>schema import</b> imports the element declarations,
attribute declarations, and type definitions from a schema into the
<a title="in-scope schema definitions" href="#dt-issd">in-scope
schema definitions</a>. <span>For each user-defined atomic type in
the schema, schema import also adds a corresponding <a title=
"constructor function" href="#dt-constructor-function">constructor
function</a>.</span></p>
</dd>
<dt><a name="GLdt-schema-import-feature" id=
"GLdt-schema-import-feature"></a>schema import feature</dt>
<dd>
<p>The <b>Schema Import Feature</b> permits the query Prolog to
contain a <a title="schema import" href="#dt-schema-import">schema
import</a>.</p>
</dd>
<dt><a name="GLdt-schema-type" id="GLdt-schema-type"></a>schema
type</dt>
<dd>
<p>A <b>schema type</b> is a type that is (or could be) defined
using the facilities of <a href="#XMLSchema">[XML Schema]</a>
(including the built-in types of <a href="#XMLSchema">[XML
Schema]</a>).</p>
</dd>
<dt><a name="GLdt-schema-validation-feature" id=
"GLdt-schema-validation-feature"></a>schema validation feature</dt>
<dd>
<p>The <b>Schema Validation Feature</b> permits a query to contain
a <code>validate</code> expression (see <a href=
"#id-validate"><b>3.13 Validate Expressions</b></a>.)</p>
</dd>
<dt><a name="GLdt-sequence" id="GLdt-sequence"></a>sequence</dt>
<dd>
<p>A <b>sequence</b> is an ordered collection of zero or more
<a title="item" href="#dt-item">items</a>.</p>
</dd>
<dt><a name="GLdt-sequence-type" id=
"GLdt-sequence-type"></a>sequence type</dt>
<dd>
<p>A <b>sequence type</b> is a type that can be expressed using the
<a href="#doc-xquery-SequenceType">SequenceType</a> syntax.
Sequence types are used whenever it is necessary to refer to a type
in an XQuery expression. The term <b>sequence type</b> suggests
that this syntax is used to describe the type of an XQuery value,
which is always a sequence.</p>
</dd>
<dt><a name="GLdt-serialization" id=
"GLdt-serialization"></a>serialization</dt>
<dd>
<p><b>Serialization</b> is the process of converting an <a title=
"XDM instance" href="#dt-data-model-instance">XDM instance</a> into
a sequence of octets (step DM4 in Figure 1.)</p>
</dd>
<dt><a name="GLdt-serialization-feature" id=
"GLdt-serialization-feature"></a>serialization feature</dt>
<dd>
<p>A conforming XQuery implementation that supports the
<b>Serialization Feature</b> <a title="must" href="#must">MUST</a>
provide means for serializing the result of a query, as specified
in <a href="#id-serialization"><b>2.2.4 Serialization</b></a>.</p>
</dd>
<dt><a name="GLdt-setter" id="GLdt-setter"></a>setter</dt>
<dd>
<p><b>Setters</b> are declarations that set the value of some
property that affects query processing, such as construction mode,
ordering mode, or default collation.</p>
</dd>
<dt><a name="GLshould" id="GLshould"></a>should</dt>
<dd>
<p><b>SHOULD</b> means that there may exist valid reasons in
particular circumstances to ignore a particular item, but the full
implications must be understood and carefully weighed before
choosing a different course.</p>
</dd>
<dt><a name="GLdt-singleton" id="GLdt-singleton"></a>singleton</dt>
<dd>
<p>A sequence containing exactly one item is called a
<b>singleton</b>.</p>
</dd>
<dt><a name="GLstable" id="GLstable"></a>stable</dt>
<dd>
<p>Document order is <b>stable</b>, which means that the relative
order of two nodes will not change during the processing of a given
<span class="xquery"><span class="xquery">query</span></span>, even
if this order is <a title="implementation dependent" href=
"#dt-implementation-dependent">implementation-dependent</a>.</p>
</dd>
<dt><a name="GLdt-static-analysis" id=
"GLdt-static-analysis"></a>static analysis phase</dt>
<dd>
<p>The <b>static analysis phase</b> depends on the expression
itself and on the <a title="static context" href=
"#dt-static-context">static context</a>. The <b>static analysis
phase</b> does not depend on input data (other than schemas).</p>
</dd>
<dt><a name="GLdt-static-context" id=
"GLdt-static-context"></a>static context</dt>
<dd>
<p>The <b>static context</b> of an expression is the information
that is available during static analysis of the expression, prior
to its evaluation.</p>
</dd>
<dt><a name="GLdt-static-error" id="GLdt-static-error"></a>static
error</dt>
<dd>
<p>A <b>static error</b> is an error that must be detected during
the static analysis phase. A syntax error is an example of a
<a title="static error" href="#dt-static-error">static
error</a>.</p>
</dd>
<dt><a name="GLdt-static-type" id="GLdt-static-type"></a>static
type</dt>
<dd>
<p>The <b>static type</b> of an expression is a type such that,
when the expression is evaluated, the resulting value will always
conform to the static type.</p>
</dd>
<dt><a name="GLdt-static-typing-extension" id=
"GLdt-static-typing-extension"></a>static typing extension</dt>
<dd>
<p>A <b>static typing extension</b> is an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> type
inference rule that infers a more precise static type than that
inferred by the type inference rules in <a href=
"#XQueryFormalSemantics">[XQuery 1.0 and XPath 2.0 Formal Semantics
(Second Edition)]</a>.</p>
</dd>
<dt><a name="GLdt-static-typing-feature" id=
"GLdt-static-typing-feature"></a>static typing feature</dt>
<dd>
<p>The <b>Static Typing Feature</b> provides support for the static
semantics defined in <a href="#XQueryFormalSemantics">[XQuery 1.0
and XPath 2.0 Formal Semantics (Second Edition)]</a>, and requires
implementations to detect and report <a title="type error" href=
"#dt-type-error">type errors</a> during the <a title=
"static analysis phase" href="#dt-static-analysis">static analysis
phase</a>.</p>
</dd>
<dt><a name="GLdt-known-collections" id=
"GLdt-known-collections"></a>statically known collections</dt>
<dd>
<p><b>Statically known collections.</b> This is a mapping from
strings onto types. The string represents the absolute URI of a
resource that is potentially available using the
<code>fn:collection</code> function. The type is the type of the
sequence of nodes that would result from calling the
<code>fn:collection</code> function with this URI as its
argument.</p>
</dd>
<dt><a name="GLdt-known-docs" id="GLdt-known-docs"></a>statically
known documents</dt>
<dd>
<p><b>Statically known documents.</b> This is a mapping from
strings onto types. The string represents the absolute URI of a
resource that is potentially available using the
<code>fn:doc</code> function. The type is the <a title=
"static type" href="#dt-static-type">static type</a> of a call to
<code>fn:doc</code> with the given URI as its literal argument.</p>
</dd>
<dt><a name="GLdt-static-collations" id=
"GLdt-static-collations"></a>statically known collations</dt>
<dd>
<p><b>Statically known collations.</b> This is an <a title=
"implementation defined" href=
"#dt-implementation-defined">implementation-defined</a> set of
(URI, collation) pairs. It defines the names of the collations that
are available for use in processing <span class=
"xquery"><span class="xquery">queries and</span></span>
expressions.</p>
</dd>
<dt><a name="GLdt-known-default-collection" id=
"GLdt-known-default-collection"></a>statically known default
collection type</dt>
<dd>
<p><b>Statically known default collection type.</b> This is the
type of the sequence of nodes that would result from calling the
<code>fn:collection</code> function with no arguments.</p>
</dd>
<dt><a name="GLdt-static-namespaces" id=
"GLdt-static-namespaces"></a>statically known namespaces</dt>
<dd>
<p><b>Statically known namespaces.</b> This is a set of (prefix,
URI) pairs that define all the namespaces that are known during
static processing of a given expression.</p>
</dd>
<dt><a name="GLdt-step" id="GLdt-step"></a>step</dt>
<dd>
<p>A <b>step</b> is a part of a <a title="path expression" href=
"#dt-path-expression">path expression</a> that generates a sequence
of items and then filters the sequence by zero or more <a title=
"predicate" href="#dt-predicate">predicates</a>. The value of the
step consists of those items that satisfy the predicates, working
from left to right. A step may be either an <a title="axis step"
href="#dt-axis-step">axis step</a> or a <a title=
"filter expression" href="#dt-filter-expression">filter
expression</a>.</p>
</dd>
<dt><a name="GLdt-string-value" id="GLdt-string-value"></a>string
value</dt>
<dd>
<p>The <b>string value</b> of a node is a string and can be
extracted by applying the <code>fn:string</code> function to the
node.</p>
</dd>
<dt><a name="GLdt-substitution-group" id=
"GLdt-substitution-group"></a>substitution group</dt>
<dd>
<p><b>Substitution groups</b> are defined in <a href=
"#XMLSchema">[XML Schema]</a> Part 1, Section 2.2.2.2. Informally,
the substitution group headed by a given element (called the
<b>head element</b>) consists of the set of elements that can be
substituted for the head element without affecting the outcome of
schema validation.</p>
</dd>
<dt><a name="GLdt-subtype-substitution" id=
"GLdt-subtype-substitution"></a>subtype substitution</dt>
<dd>
<p>The use of a value whose <a title="dynamic type" href=
"#dt-dynamic-type">dynamic type</a> is derived from an expected
type is known as <b>subtype substitution</b>.</p>
</dd>
<dt><a name="GLsymbol" id="GLsymbol"></a>symbol</dt>
<dd>
<p>Each rule in the grammar defines one <b>symbol</b>, using the
following format:</p>
<div class="exampleInner">
<pre>
symbol ::= expression
</pre></div>
</dd>
<dt><a name="GLsymbolseparators" id="GLsymbolseparators"></a>symbol
separators</dt>
<dd>
<p><a title="whitespace" href="#Whitespace">Whitespace</a> and
<a href="#doc-xquery-Comment">Comments</a> function as <b>symbol
separators</b>. For the most part, they are not mentioned in the
grammar, and may occur between any two terminal symbols mentioned
in the grammar, except where that is forbidden by the <a href=
"#ws-explicit">/* ws: explicit */</a> annotation in the EBNF, or by
the <a href="#parse-note-xml-version">/* xgs: xml-version */</a>
annotation.</p>
</dd>
<dt><a name="GLdt-target-namespace" id=
"GLdt-target-namespace"></a>target namespace</dt>
<dd>
<p>Each imported schema or module is identified by its <b>target
namespace</b>, which is the namespace of the objects (such as
elements or functions) that are defined by the schema or
module.</p>
</dd>
<dt><a name="GLterminal" id="GLterminal"></a>terminal</dt>
<dd>
<p>A <b>terminal</b> is a symbol or string or pattern that can
appear in the right-hand side of a rule, but never appears on the
left hand side in the main grammar, although it may appear on the
left-hand side of a rule in the grammar for terminals.</p>
</dd>
<dt><a name="GLdt-type-annotation" id=
"GLdt-type-annotation"></a>type annotation</dt>
<dd>
<p>Each element node and attribute node in an <a title=
"XDM instance" href="#dt-data-model-instance">XDM instance</a> has
a <b>type annotation</b> (referred to in <a href=
"#datamodel">[XQuery 1.0 and XPath 2.0 Data Model (Second
Edition)]</a> as its <code>type-name</code> property.) The type
annotation of a node is a <a title="schema type" href=
"#dt-schema-type">schema type</a> that describes the relationship
between the <a title="string value" href="#dt-string-value">string
value</a> of the node and its <a title="typed value" href=
"#dt-typed-value">typed value</a>.</p>
</dd>
<dt><a name="GLdt-type-error" id="GLdt-type-error"></a>type
error</dt>
<dd>
<p>A <b>type error</b> may be raised during the static analysis
phase or the dynamic evaluation phase. During the static analysis
phase, a <a title="type error" href="#dt-type-error">type error</a>
occurs when the <a title="static type" href=
"#dt-static-type">static type</a> of an expression does not match
the expected type of the context in which the expression occurs.
During the dynamic evaluation phase, a <a title="type error" href=
"#dt-type-error">type error</a> occurs when the <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a> of a value
does not match the expected type of the context in which the value
occurs.</p>
</dd>
<dt><a name="GLdt-type-promotion" id="GLdt-type-promotion"></a>type
promotion</dt>
<dd>
<p>Under certain circumstances, an atomic value can be promoted
from one type to another. <b>Type promotion</b> is used in
evaluating function calls (see <a href=
"#id-function-calls"><b>3.1.5 Function Calls</b></a>)<span class=
"xquery"><span class="xquery">, <code>order by</code> clauses (see
<a href="#id-orderby-return"><b>3.8.3 Order By and Return
Clauses</b></a>),</span></span> and operators that accept numeric
or string operands (see <a href="#mapping"><b>B.2 Operator
Mapping</b></a>).</p>
</dd>
<dt><a name="GLdt-typed-value" id="GLdt-typed-value"></a>typed
value</dt>
<dd>
<p>The <b>typed value</b> of a node is a sequence of atomic values
and can be extracted by applying the <code>fn:data</code> function
to the node.</p>
</dd>
<dt><a name="GLdt-undefined" id="GLdt-undefined"></a>undefined</dt>
<dd>
<p>In certain situations a value is said to be <b>undefined</b>
(for example, the value of the context item, or the typed value of
an element node). This term indicates that the property in question
has no value and that any attempt to use its value results in an
error.</p>
</dd>
<dt><a name="GLdt-udf" id="GLdt-udf"></a>user-defined function</dt>
<dd>
<p>For a <b>user-defined function</b>, the function declaration
includes an expression called the <b>function body</b> that defines
how the result of the function is computed from its parameters.</p>
</dd>
<dt><a name="GLdt-value" id="GLdt-value"></a>value</dt>
<dd>
<p>In the <a title="data model" href="#dt-datamodel">data
model</a>, a <b>value</b> is always a <a title="sequence" href=
"#dt-sequence">sequence</a>.</p>
</dd>
<dt><a name="GLdt-variable-depends" id=
"GLdt-variable-depends"></a>variable depends</dt>
<dd>
<p>A variable <code>$x</code> <b>depends</b> on a variable
<code>$y</code> or a function <code>f2</code> if a reference to
<code>$y</code> or <code>f2</code> appears in the initializing
expression of <code>$x</code>, or if there exists a variable
<code>$z</code> or a function <code>f3</code> such that
<code>$x</code> <a title="variable depends" href=
"#dt-variable-depends">depends</a> on <code>$z</code> or
<code>f3</code> and <code>$z</code> or <code>f3</code> <a title=
"function depends" href="#dt-function-depends">depends</a> on
<code>$y</code> or <code>f2</code>.</p>
</dd>
<dt><a name="GLdt-variable-reference" id=
"GLdt-variable-reference"></a>variable reference</dt>
<dd>
<p>A <b>variable reference</b> is a QName preceded by a $-sign.</p>
</dd>
<dt><a name="GLdt-variable-values" id=
"GLdt-variable-values"></a>variable values</dt>
<dd>
<p><b>Variable values</b>. This is a set of (expanded QName, value)
pairs. It contains the same <a title="expanded QName" href=
"#dt-expanded-qname">expanded QNames</a> as the <a title=
"in-scope variables" href="#dt-in-scope-variables">in-scope
variables</a> in the <a title="static context" href=
"#dt-static-context">static context</a> for the expression. The
expanded QName is the name of the variable and the value is the
dynamic value of the variable, which includes its <a title=
"dynamic type" href="#dt-dynamic-type">dynamic type</a>.</p>
</dd>
<dt><a name="GLdt-version-declaration" id=
"GLdt-version-declaration"></a>version declaration</dt>
<dd>
<p>Any <a title="module" href="#dt-module">module</a> may contain a
<b>version declaration</b>. If present, the version declaration
occurs at the beginning of the <a title="module" href=
"#dt-module">module</a> and identifies the applicable XQuery syntax
and semantics for the <a title="module" href=
"#dt-module">module</a>.</p>
</dd>
<dt><a name="GLdt-warning" id="GLdt-warning"></a>warning</dt>
<dd>
<p>In addition to <a title="static error" href=
"#dt-static-error">static errors</a>, <a title="dynamic error"
href="#dt-dynamic-error">dynamic errors</a>, and <a title=
"type error" href="#dt-type-error">type errors</a>, an XQuery
implementation may raise <b>warnings</b>, either during the
<a title="static analysis phase" href="#dt-static-analysis">static
analysis phase</a> or the <a title="dynamic evaluation phase" href=
"#dt-dynamic-evaluation">dynamic evaluation phase</a>. The
circumstances in which warnings are raised, and the ways in which
warnings are handled, are <a title="implementation defined" href=
"#dt-implementation-defined">implementation-defined</a>.</p>
</dd>
<dt><a name="GLWhitespace" id="GLWhitespace"></a>whitespace</dt>
<dd>
<p>A <b>whitespace</b> character is any of the characters defined
by <a href=
"http://www.w3.org/TR/REC-xml/#NT-S">[http://www.w3.org/TR/REC-xml/#NT-S]</a>.</p>
</dd>
<dt><a name="GLdt-anyAtomicType" id=
"GLdt-anyAtomicType"></a>xs:anyAtomicType</dt>
<dd>
<p><code>xs:anyAtomicType</code> is an atomic type that includes
all atomic values (and no values that are not atomic). Its base
type is <code>xs:anySimpleType</code> from which all simple types,
including atomic, list, and union types, are derived. All primitive
atomic types, such as <code>xs:decimal</code> and
<code>xs:string</code>, have <code>xs:anyAtomicType</code> as their
base type.</p>
</dd>
<dt><a name="GLdt-dayTimeDuration" id=
"GLdt-dayTimeDuration"></a>xs:dayTimeDuration</dt>
<dd>
<p><code>xs:dayTimeDuration</code> is derived by restriction from
<code>xs:duration</code>. The lexical representation of
<code>xs:dayTimeDuration</code> is restricted to contain only day,
hour, minute, and second components.</p>
</dd>
<dt><a name="GLdt-untyped" id="GLdt-untyped"></a>xs:untyped</dt>
<dd>
<p><code>xs:untyped</code> is used as the <a title=
"type annotation" href="#dt-type-annotation">type annotation</a> of
an element node that has not been validated, or has been validated
in <code>skip</code> mode.</p>
</dd>
<dt><a name="GLdt-untypedAtomic" id=
"GLdt-untypedAtomic"></a>xs:untypedAtomic</dt>
<dd>
<p><code>xs:untypedAtomic</code> is an atomic type that is used to
denote untyped atomic data, such as text that has not been assigned
a more specific type.</p>
</dd>
<dt><a name="GLdt-yearMonthDuration" id=
"GLdt-yearMonthDuration"></a>xs:yearMonthDuration</dt>
<dd>
<p><code>xs:yearMonthDuration</code> is derived by restriction from
<code>xs:duration</code>. The lexical representation of
<code>xs:yearMonthDuration</code> is restricted to contain only
year and month components.</p>
</dd>
</dl>
</div>
<div class="xquery">
<div class="div1">
<h2><a name="id-example-applications" id=
"id-example-applications"></a>I Example Applications
(Non-Normative)</h2>
<p>This section contains examples of several important classes of
queries that can be expressed using XQuery. The applications
described here include joins across multiple data sources, grouping
and aggregation, queries based on sequential relationships,
recursive transformations, and selection of distinct combinations
of values.</p>
<div class="div2">
<h3><a name="id-joins" id="id-joins"></a>I.1 Joins</h3>
<p>Joins, which combine data from multiple sources into a single
result, are a very important type of query. In this section we will
illustrate how several types of joins can be expressed in XQuery.
We will base our examples on the following three documents:</p>
<ol class="enumar">
<li>
<p>A document named <code>parts.xml</code> that contains many
<code>part</code> elements; each <code>part</code> element in turn
contains <code>partno</code> and <code>description</code>
subelements.</p>
</li>
<li>
<p>A document named <code>suppliers.xml</code> that contains many
<code>supplier</code> elements; each <code>supplier</code> element
in turn contains <code>suppno</code> and <code>suppname</code>
subelements.</p>
</li>
<li>
<p>A document named <code>catalog.xml</code> that contains
information about the relationships between suppliers and parts.
The catalog document contains many <code>item</code> elements, each
of which in turn contains <code>partno</code>, <code>suppno</code>,
and <code>price</code> subelements.</p>
</li>
</ol>
<p>A conventional ("inner") join returns information from two or
more related sources, as illustrated by the following example,
which combines information from three documents. The example
generates a "descriptive catalog" derived from the catalog
document, but containing part descriptions instead of part numbers
and supplier names instead of supplier numbers. The new catalog is
ordered alphabetically by part description and secondarily by
supplier name.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;descriptive-catalog&gt;
   { 
     for $i in fn:doc("catalog.xml")/items/item,
         $p in fn:doc("parts.xml")/parts/part[partno = $i/partno],
         $s in fn:doc("suppliers.xml")/suppliers
                  /supplier[suppno = $i/suppno]
     order by $p/description, $s/suppname
     return
        &lt;item&gt;
           {
           $p/description,
           $s/suppname,
           $i/price
           }
        &lt;/item&gt;
   }
&lt;/descriptive-catalog&gt;
</pre></div>
</div>
<p>The previous query returns information only about parts that
have suppliers and suppliers that have parts. An <b>outer join</b>
is a join that preserves information from one or more of the
participating sources, including elements that have no matching
element in the other source. For example, a <b>left outer join</b>
between suppliers and parts might return information about
suppliers that have no matching parts.</p>
<p>The following query demonstrates a left outer join. It returns
names of all the suppliers in alphabetic order, including those
that supply no parts. In the result, each supplier element contains
the descriptions of all the parts it supplies, in alphabetic
order.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
for $s in fn:doc("suppliers.xml")/suppliers/supplier
order by $s/suppname
return
   &lt;supplier&gt;
      { 
        $s/suppname,
        for $i in fn:doc("catalog.xml")/items/item
                 [suppno = $s/suppno],
            $p in fn:doc("parts.xml")/parts/part
                 [partno = $i/pno]
        order by $p/description
        return $p/description 
      }
   &lt;/supplier&gt;
</pre></div>
</div>
<p>The previous query preserves information about suppliers that
supply no parts. Another type of join, called a <b>full outer
join</b>, might be used to preserve information about both
suppliers that supply no parts and parts that have no supplier. The
result of a full outer join can be structured in any of several
ways. The following query generates a list of <code>supplier</code>
elements, each containing nested <code>part</code> elements for the
parts that it supplies (if any), followed by a list of
<code>part</code> elements for the parts that have no supplier.
This might be thought of as a "supplier-centered" full outer join.
Other forms of outer join queries are also possible.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;master-list&gt;
 {
    for $s in fn:doc("suppliers.xml")/suppliers/supplier
    order by $s/suppname
    return
        &lt;supplier&gt;
           { 
             $s/suppname,
             for $i in fn:doc("catalog.xml")/items/item
                     [suppno = $s/suppno],
                 $p in fn:doc("parts.xml")/parts/part
                     [partno = $i/partno]
             order by $p/description
             return
                &lt;part&gt;
                   {
                     $p/description,
                     $i/price
                   }
                &lt;/part&gt; 
           }
        &lt;/supplier&gt; 
    ,
    (: parts that have no supplier :)
    &lt;orphan-parts&gt;
       { for $p in fn:doc("parts.xml")/parts/part
         where fn:empty(fn:doc("catalog.xml")/items/item
               [partno = $p/partno] )
         order by $p/description
         return $p/description 
       }
    &lt;/orphan-parts&gt;
 }
&lt;/master-list&gt;
</pre></div>
</div>
<p>The previous query uses an element constructor to enclose its
output inside a <code>master-list</code> element. The concatenation
operator (",") is used to combine the two main parts of the query.
The result is an ordered sequence of <code>supplier</code> elements
followed by an <code>orphan-parts</code> element that contains
descriptions of all the parts that have no supplier.</p>
</div>
<div class="div2">
<h3><a name="id-grouping" id="id-grouping"></a>I.2 Grouping</h3>
<p>Many queries involve forming data into groups and applying some
aggregation function such as <code>fn:count</code> or
<code>fn:avg</code> to each group. The following example shows how
such a query might be expressed in XQuery, using the catalog
document defined in the previous section.</p>
<p>This query finds the part number and average price for parts
that have at least 3 suppliers.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
for $pn in fn:distinct-values(
      fn:doc("catalog.xml")/items/item/partno)
let $i := fn:doc("catalog.xml")/items/item[partno = $pn]
where fn:count($i) &gt;= 3
order by $pn
return 
   &lt;well-supplied-item&gt;
      &lt;partno&gt; {$pn} &lt;/partno&gt;
      &lt;avgprice&gt; {fn:avg($i/price)} &lt;/avgprice&gt;
   &lt;/well-supplied-item&gt;
</pre></div>
</div>
<p>The <code>fn:distinct-values</code> function in this query
eliminates duplicate part numbers from the set of all part numbers
in the catalog document. The result of
<code>fn:distinct-values</code> is a sequence in which order is not
significant.</p>
<p>Note that <code>$pn</code>, bound by a for clause, represents an
individual part number, whereas <code>$i</code>, bound by a let
clause, represents a set of items which serves as argument to the
aggregate functions <code>fn:count($i)</code> and
<code>fn:avg($i/price)</code>. The query uses an element
constructor to enclose each part number and average price in a
containing element called <code>well-supplied-item</code>.</p>
<p>The method illustrated above generalizes easily to grouping by
more than one data value. For example, consider a census document
containing a sequence of <code>person</code> elements, each with
subelements named <code>state</code>, <code>job</code>, and
<code>income</code>. A census analyst might need to prepare a
report listing the average <code>income</code> for each combination
of <code>state</code> and <code>job</code>. This report might be
produced using the following query:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
for $s in fn:distinct-values(
        fn:doc("census.xml")/census/person/state),
    $j in fn:distinct-values(
        fn:doc("census.xml")/census/person/job)
let $p := fn:doc("census.xml")/census/person
        [state = $s and job = $j]
order by $s, $j
return 
   if (fn:exists($p)) then
      &lt;group&gt;
         &lt;state&gt; {$s} &lt;/state&gt;
         &lt;job&gt; {$j} &lt;/job&gt;
         &lt;avgincome&gt; {fn:avg($p/income)} &lt;/avgincome&gt;
      &lt;/group&gt;
   else ()
</pre></div>
</div>
<p>The <code>if-then-else</code> expression in the above example
prevents generation of groups that contain no data. For example,
the census data may contain some persons who live in Nebraska, and
some persons whose job is Deep Sea Fisherman, but no persons who
live in Nebraska and have the job of Deep Sea Fisherman. If output
groups are desired for all possible combinations of states and
jobs, the <code>if-then-else</code> expression can be omitted from
the query. In this case, the output may include "empty" groups such
as the following:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
&lt;group&gt;
   &lt;state&gt;Nebraska&lt;/state&gt;
   &lt;job&gt;Deep Sea Fisherman&lt;/job&gt;
   &lt;avgincome/&gt;
&lt;/group&gt;
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-queries-on-sequence" id=
"id-queries-on-sequence"></a>I.3 Queries on Sequence</h3>
<p>XQuery uses the <code>&lt;&lt;</code> and <code>&gt;&gt;</code>
operators to compare nodes based on document order. Although these
operators are quite simple, they can be used to express complex
queries for XML documents in which sequence is meaningful. The
first two queries in this section involve a surgical report that
contains <code>procedure</code>, <code>incision</code>,
<code>instrument</code>, <code>action</code>, and
<code>anesthesia</code> elements.</p>
<p>The following query returns all the <code>action</code> elements
that occur between the first and second <code>incision</code>
elements inside the first procedure. The original document order
among these nodes is preserved in the result of the query.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $proc := /report/procedure[1]
for $i in $proc//action
where $i &gt;&gt; ($proc//incision)[1]
   and $i &lt;&lt; ($proc//incision)[2]
return $i
</pre></div>
</div>
<p>It is worth noting here that document order is defined in such a
way that a node is considered to precede its descendants in
document order. In the surgical report, an <code>action</code> is
never part of an <code>incision</code>, but an
<code>instrument</code> is. Since the <code>&gt;&gt;</code>
operator is based on document order, the predicate <code>$i
&gt;&gt; ($proc//incision)[1]</code> is true for any
<code>instrument</code> element that is a descendant of the first
<code>incision</code> element in the first procedure.</p>
<p>For some queries, it may be helpful to define a function that
can test whether a node precedes another node without being its
ancestor. The following function returns <code>true</code> if its
first operand precedes its second operand but is not an ancestor of
its second operand; otherwise it returns <code>false</code>:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare function local:precedes($a as node(), $b as node()) 
   as boolean
   {
      $a &lt;&lt; $b
        and
      fn:empty($a//node() intersect $b) 
   };
</pre></div>
</div>
<p>Similarly, a <code>local:follows</code> function could be
written:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare function local:follows($a as node(), $b as node()) 
   as boolean
   {
      $a &gt;&gt; $b
        and
      fn:empty($b//node() intersect $a) 
   };
</pre></div>
</div>
<p>Using the <code>local:precedes</code> function, we can write a
query that finds <code>instrument</code> elements between the first
two incisions, excluding from the query result any
<code>instrument</code> that is a descendant of the first
<code>incision</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $proc := /report/procedure[1]
for $i in $proc//instrument
where local:precedes(($proc//incision)[1], $i)
   and local:precedes($i, ($proc//incision)[2])
return $i
</pre></div>
</div>
<p>The following query reports incisions for which no prior
anesthesia was recorded in the surgical report. Since an
<code>anesthesia</code> is never part of an <code>incision</code>,
we can use <code>&lt;&lt;</code> instead of the less-efficient
<code>local:precedes</code> function:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
for $proc in /report/procedure
where some $i in $proc//incision satisfies
         fn:empty($proc//anesthesia[. &lt;&lt; $i])
return $proc
</pre></div>
</div>
<p>In some documents, particular sequences of elements may indicate
a logical hierarchy. This is most commonly true of HTML. The
following query returns the introduction of an XHTML document,
wrapping it in a <code>div</code> element. In this example, we
assume that an <code>h2</code> element containing the text
"Introduction" marks the beginning of the introduction, and the
introduction continues until the next <code>h2</code> or
<code>h1</code> element, or the end of the document, whichever
comes first.</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
let $intro := //h2[text()="Introduction"],
    $next-h := //(h1|h2)[. &gt;&gt; $intro][1]
return
   &lt;div&gt;
     {
       $intro,
       if (fn:empty($next-h))
         then //node()[. &gt;&gt; $intro]
         else //node()[. &gt;&gt; $intro and . &lt;&lt; $next-h]
     }
   &lt;/div&gt;
</pre></div>
</div>
<p>Note that the above query makes explicit the hierarchy that was
implicit in the original document. In this example, we assume that
the <code>h2</code> element containing the text "Introduction" has
no subelements.</p>
</div>
<div class="div2">
<h3><a name="id-recursive-transformations" id=
"id-recursive-transformations"></a>I.4 Recursive
Transformations</h3>
<p>Occasionally it is necessary to scan over a hierarchy of
elements, applying some transformation at each level of the
hierarchy. In XQuery this can be accomplished by defining a
recursive function. In this section we will present two examples of
such recursive functions.</p>
<p>Suppose that we need to compute a table of contents for a given
document by scanning over the document, retaining only elements
named <code>section</code> or <code>title</code>, and preserving
the hierarchical relationships among these elements. For each
<code>section</code>, we retain subelements named
<code>section</code> or <code>title</code>; but for each
<code>title</code>, we retain the full content of the element. This
might be accomplished by the following recursive function:</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare function local:sections-and-titles($n as node()) as node()?
   {
   if (fn:local-name($n) = "section")
   then element
          { fn:local-name($n) }
          { for $c in $n/* return local:sections-and-titles($c) }
   else if (fn:local-name($n) = "title")
   then $n
   else ( )
   };
</pre></div>
</div>
<p>The "skeleton" of a given document, containing only its sections
and titles, can then be obtained by invoking the
<code>local:sections-and-titles</code> function on the root node of
the document, as follows:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
local:sections-and-titles(fn:doc("cookbook.xml"))
</pre></div>
</div>
<p>As another example of a recursive transformation, suppose that
we wish to scan over a document, transforming every attribute named
<code>color</code> to an element named <code>color</code>, and
every element named <code>size</code> to an attribute named
<code>size</code>. This can be accomplished by the following
recursive function (note that the element constructor in case
<code>$e</code> generates attributes before child elements):</p>
<div class="frag-prolog-parse-test">
<div class="exampleInner">
<pre>
declare function local:swizzle($n as node()) as node() 
  { 
   typeswitch($n)
     case $a as attribute(color)
       return element color { fn:string($a) } 
     case $es as element(size) 
       return attribute size { fn:string($es) } 
     case $e as element() 
       return element 
         { fn:local-name($e) } 
         { for $c in 
             ($e/@* except $e/@color,     (: attr -&gt; attr :)
              $e/size,                    (: elem -&gt; attr :)
              $e/@color,                  (: attr -&gt; elem :)
              $e/node() except $e/size )  (: elem -&gt; elem :)
           return local:swizzle($c) }
     case $d as document-node() 
       return document 
         { for $c in $d/* return local:swizzle($c) } 
     default return $n 
  };
</pre></div>
</div>
<p>The transformation can be applied to a whole document by
invoking the <code>local:swizzle</code> function on the root node
of the document, as follows:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
local:swizzle(fn:doc("plans.xml"))
</pre></div>
</div>
</div>
<div class="div2">
<h3><a name="id-select-distinct" id="id-select-distinct"></a>I.5
Selecting Distinct Combinations</h3>
<p>It is sometimes necessary to search through a set of data to
find all the distinct combinations of a given list of properties.
For example, an input data set might consist of a large set of
<code>order</code> elements, each of which has the same basic
structure, as illustrated by the following example:</p>
<div class="exampleInner">
<pre>
&lt;order&gt;
   &lt;date&gt;2003-10-15&lt;/date&gt;
   &lt;product&gt;Dress Shirt&lt;/product&gt;
   &lt;size&gt;M&lt;/size&gt;
   &lt;color&gt;Blue&lt;/color&gt;
   &lt;supplier&gt;Fashion Trends&lt;/supplier&gt;
   &lt;quantity&gt;50&lt;/quantity&gt;
&lt;/order&gt;
</pre></div>
<p>From this data set, a user might wish to find all the distinct
combinations of <code>product</code>, <code>size</code>, and
<code>color</code> that occur together in an <code>order</code>.
The following query returns this list, enclosing each distinct
combination in a new element named <code>option</code>:</p>
<div class="parse-test">
<div class="exampleInner">
<pre>
for $p in fn:distinct-values(/orders/order/product),
    $s in fn:distinct-values(/orders/order/size),
    $c in fn:distinct-values(/orders/order/color)
    order by $p, $s, $c
    return
       if (fn:exists(/orders/order[product eq $p
                and size eq $s and color eq $c]))
       then
          &lt;option&gt;
             &lt;product&gt;{$p}&lt;/product&gt;
             &lt;size&gt;{$s}&lt;/size&gt;
             &lt;color&gt;{$c}&lt;/color&gt;
          &lt;/option&gt;
       else ()
</pre></div>
</div>
</div>
</div>
</div>
<div class="xquery">
<div class="div1">
<h2><a name="id-module-handling" id="id-module-handling"></a>J
Guidance for Handling of Modules (Non-Normative)</h2>
<p>This specification gives considerable flexibility to
implementations in the way that modules are implemented, in
particular, in the way that module URIs and their location URIs are
interpreted. This flexibility is intentional, because XQuery
implementations are designed to operate in a wide variety of
environments, and some of those environments impose constraints.
Nevertheless, in the interests of interoperability, the Working
Group hopes that it will be useful to offer some suggestions for
how implementations might choose to interpret the specification, in
the absence of implementation factors that make a different
interpretation necessary.</p>
<div class="div2">
<h3><a name="id-module-handling-module-uris" id=
"id-module-handling-module-uris"></a>J.1 Module URIs</h3>
<p>Generally, Module URIs should be treated in the same way as
other namespace URIs.</p>
<p>Query authors should use a string that is a legal absolute IRI.
Implementors should accept any string of Unicode characters. Module
URIs should be compared using the Unicode codepoint collation
rather than any concept of semantic equivalence.</p>
<p>Implementations may provide mechanisms allowing the module URI
to be used as input to a process that delivers the module as a
resource, for example a catalog, module repository, or URI
resolver. For interoperability, such mechanisms should not prevent
the user from choosing an arbitrary URI for naming a module.</p>
<p>Similarly, implementations may perform syntactic transformations
on the module URI to obtain the names of related resources, for
example to implement a convention relating the name or location of
compiled code to the module URI; but again, such mechanisms should
not prevent the user from choosing an arbitrary module URI.</p>
<p>As with other namespace URIs, common practice is often to use
module URIs whose scheme is "http" and whose authority part uses a
DNS domain name under the control of the user.</p>
<p>The specifications allow, and some users might consider it good
practice, for the module URI of a function library to be the same
as the namespace URI of the XML vocabulary manipulated by the
functions in that library.</p>
</div>
<div class="div2">
<h3><a name="id-module-handling-multiple-same" id=
"id-module-handling-multiple-same"></a>J.2 Multiple Modules with
the same Module URI</h3>
<p>The specifications allow several different modules with the same
Module URI to participate in a query.</p>
<p>Although other interpretations are possible, it is suggested
that in such cases implementations should require the names of
global variables and functions to be unique within the query as a
whole: that is, if two modules with the same module URI participate
in a query, the names of their global variables and functions
should not overlap.</p>
<p>If one module contains an "import module" declaration for the
module URI M, then all global variables and functions declared in
participating modules whose module URI is M should be accessible in
the importing module, regardless whether the participation of the
imported module was directly due to this "import module"
declaration.</p>
<p>There should only be one instance of a global variable with any
given name. For example, if a global variable V is initialized
using an element constructor, then there should only be one
instance of this element, even if the module in which V is declared
is imported by several other modules.</p>
<p>(A different approach to this might be used in an environment
where a group of modules can be compiled as a unit; in such cases a
module used within the compiled unit might be considered distinct
from an instance of the same module imported from elsewhere in the
query.)</p>
</div>
<div class="div2">
<h3><a name="id-module-handling-location-uris" id=
"id-module-handling-location-uris"></a>J.3 Location URIs</h3>
<p>The term "location URIs" is used here to refer to the URIs in
the "at" clause of an "import module" declaration.</p>
<p>Products should (by default or at user option) take account of
all the location URIs in an "import module" declaration, treating
each location URI as a reference to a module with the specified
module URI. Location URIs should be made absolute with respect to
the static base URI of the query module containing the "import
module" declaration where they appear. The mapping from location
URIs to module source code or compiled code MAY be done in any way
convenient to the implementation. If possible given the product's
architecture, security requirements, etc, the product should allow
this to fetch the source code of the module to use the standard web
mechanisms for dereferencing URIs in standard schemes such as the
"http" URI scheme.</p>
<p>When the same absolutized location URI is used more than once,
either in the same "import module" declaration or in different
"import module" declarations within the same query, a single copy
of the resource containing the module should be loaded. When
different absolutized location URIs are used, each should result in
a single module being loaded, unless the implementation is able to
determine that the different URIs are references to the same
resource. No error due to duplicate variable or functions names
should arise from the same module being imported more than once, so
long as the absolute location URI is the same in each case.</p>
<p>By default, implementations should report a static error if a
location URI cannot be resolved. However, this is not intended to
disallow recovery strategies being used if appropriate.</p>
</div>
<div class="div2">
<h3><a name="id-module-handling-cycles" id=
"id-module-handling-cycles"></a>J.4 Cycles</h3>
<p>It is not an error to have a cycle in the import graph, either
at the level of module URIs or at the level of location URIs. The
only rules concerning cycles affect the relationships between
functions and variables defined in different modules.</p>
</div>
</div>
</div>
<div class="div1">
<h2><a name="id-revisions-log" id="id-revisions-log"></a>K Changes
since the First Edition (Non-Normative)</h2>
<div class="xquery">
<p class="xquery">This version of the XQuery specification was
created by applying the errata from <a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html">Errata
for XQuery 1.0: An XML Query Language</a> to the <a href=
"http://www.w3.org/TR/2007/REC-xquery-20070123/">XQuery 1.0
Recommendation</a>. No other substantive changes have been
made.</p>
</div>
<div class="xquery">
<table border="1" cellpadding="5" width="100%" class="xquery">
<thead>
<tr>
<td>Erratum</td>
<td>Bugzilla</td>
<td>Category</td>
<td>Description</td>
</tr>
</thead>
<tbody>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E1">XQ.E1</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4151">4151</a></td>
<td>substantive</td>
<td>Specifies that error XQTY0086 applies to copied attribute nodes
as well as copied element nodes, including copied attribute nodes
that have no parent. The error is raised when construction-mode
calls for the type of a QName to be preserved, but
copy-namespaces-mode does not preserve the namespace binding that
is needed by the QName.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E2">XQ.E2</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=3637">3637</a></td>
<td>substantive</td>
<td>Reverses the order of Rules 1 and 2 in XQuery Section 3.7.3.1,
Computed Element Constructors (processing of content sequence).
Also reverses the order of Rules 1 and 2 in Section 3.7.3.3,
Document Node Constructors. These changes are necessary in order to
cause document nodes to be replaced by their children before
adjacent text nodes are merged.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E3">XQ.E3</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4868">4868</a></td>
<td>editorial</td>
<td>For valid syntax, adds parentheses to the expansion for leading
"/" and leading "//" in a path expression.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E4">XQ.E4</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4446">4446</a></td>
<td>substantive</td>
<td>Adds more details to the rules defining permissible expression
rewrites for optimization and other purposes.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E5">XQ.E5</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4873">4873</a></td>
<td>substantive</td>
<td>Clarifies the conditions under which a castable expression may
raise an error.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E6">XQ.E6</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4321">4321</a></td>
<td>substantive</td>
<td>Tightens the rules for the in-scope schema definitions that
must be present in an importing module. For example, if the
imported module contains a function definition that includes a
parameter of type schema-element(EN) and that function is
referenced in the importing module, then the importing module must
have an in-scope element declaration for EN.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E7">XQ.E7</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4353">4353</a></td>
<td>substantive</td>
<td>In Section 3.13 (Validate Expression), Rule 3c, deletes
"Identity-constraint Satisfied" from the list of rules that are not
applied during validation. This rule must be applied.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E8">XQ.E8</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4418">4418</a></td>
<td>substantive</td>
<td>Deletes error code XQST0073, because it is redundant to error
code XQST0093.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E9">XQ.E9</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4443">4443</a></td>
<td>substantive</td>
<td>Specifies that, in a computed attribute constructor, if the
QName of the constructed attribute has a namespace URI but no
prefix, an implementation-dependent prefix is generated.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E10">XQ.E10</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5035">5035</a></td>
<td>editorial</td>
<td>Clarifies that the default initial static type of the context
item is undefined.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E11">XQ.E11</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5207">5207</a></td>
<td>editorial</td>
<td>Clarifies behavior of node constructors when base-URI in static
context is undefined.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E12">XQ.E12</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5351">5351</a>
<a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6559">6559</a></td>
<td>substantive</td>
<td>Specifies that an error results if the PITarget specified in a
SequenceType of form processing-instruction(PITarget) is not a
syntactically valid NCName.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E13">XQ.E13</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5083">5083</a></td>
<td>substantive</td>
<td>Disallows enclosed expressions inside a namespace declaration
attribute, and clarifies handling of consecutive curly-braces,
consecutive single-quotes, and consecutive double-quotes inside
attribute values.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E14">XQ.E14</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5224">5224</a></td>
<td>editorial</td>
<td>Calls attention to the entry in Appendix C that defines the
initial values for context item, position, and size, which can be
referenced in initializing expressions in variable
declarations.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E15">XQ.E15</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5261">5261</a></td>
<td>editorial</td>
<td>Removes references to error code FORG0001 from description of
cast expression. Replaces them with a reference to Functions and
Operators for normative description of error behavior.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E16">XQ.E16</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5471">5471</a></td>
<td>editorial</td>
<td>Deletes unnecessary reference to RFC2396 from Normative
References. This item is never referenced in the normative
text.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E17">XQ.E17</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5290">5290</a></td>
<td>substantive</td>
<td>Specifies that, in the order-by clause of a FLWOR expression, a
user-specified collation applies only if the value of the ordering
expression is of type xs:string or is convertible to
xs:string.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E18">XQ.E18</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5223">5223</a></td>
<td>substantive</td>
<td>Specifies that general comparisons cast an untyped operand to
the primitive base type of the other operand rather than to the
most specific type of the other operand.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E19">XQ.E19</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=4463">4463</a></td>
<td>substantive</td>
<td>Specifies rules that prevent the redefinition of certain
predefined namespace prefixes.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E20">XQ.E20</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5984">5984</a></td>
<td>editorial</td>
<td>Corrects a list of examples of primitive atomic types.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E21">XQ.E21</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5347">5347</a></td>
<td>substantive</td>
<td>Allows (and encourages) the use of XML 1.0 editions newer than
the Third Edition.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E22">XQ.E22</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6027">6027</a></td>
<td>substantive</td>
<td>Specifies conformance criteria for syntax extensions.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E23">XQ.E23</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6287">6287</a></td>
<td>editorial</td>
<td>Defines the meaning of "undefined" for Data Model
properties.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E24">XQ.E24</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5727">5727</a></td>
<td>substantive</td>
<td>Clarifications on parsing leading / in XPath expressions.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E25">XQ.E25</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6557">6557</a></td>
<td>editorial</td>
<td>Adds a missing word to an error description.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E26">XQ.E26</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5876">5876</a></td>
<td>substantive</td>
<td>Corrects the description of precedence with respect to
parentheses and square brackets.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E27">XQ.E27</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=5351">5351</a></td>
<td>substantive</td>
<td>Specifies that leading and trailing whitespace are stripped
from a PITarget specified in a SequenceType of form
processing-instruction(PITarget) before it is tested to see if it
is a syntactically valid NCName. Also makes the description of the
error introduced in E12 more precise. If accepted, this supersedes
E12.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E28">XQ.E28</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6716">6716</a></td>
<td>substantive</td>
<td>A new non-normative appendix designed to give guidance on the
handling of modules.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E29">XQ.E29</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6693">6693</a>
<a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6717">6717</a></td>
<td>editorial</td>
<td>State more explicitly that user-defined types in an imported
schema add constructors for these types to the set of known
function signatures.</td>
</tr>
<tr>
<td><a href=
"http://www.w3.org/XML/2007/qt-errata/xquery-errata.html#E30">XQ.E30</a></td>
<td><a href=
"http://www.w3.org/Bugs/Public/show_bug.cgi?id=6737">6737</a></td>
<td>editorial</td>
<td>Fixes an example by replacing the undefined variable
&lt;partno&gt; {$p} &lt;/partno&gt; with &lt;partno&gt; {$pn}
&lt;/partno&gt;).</td>
</tr>
<tr class="xquery">
<td>(None.)</td>
<td>(None.)</td>
<td>editorial</td>
<td>In <a href="#id-mime-type"><b>G The application/xquery Media
Type</b></a>, a new section <a href=
"#id-published-specification"><b>G.2.2 Published
specification</b></a> has been created.</td>
</tr>
<tr class="xquery">
<td>(None.)</td>
<td>(None.)</td>
<td>Editorial</td>
<td>In <a href="#id-intended-usage"><b>G.2.5 Intended
Usage</b></a>, the text was replaced with the word "COMMON".</td>
</tr>
</tbody>
</table>
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