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</style><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css" charset="utf-8"></head><body style="display: inherit; "><div class="head"><p><a href="http://www.w3.org/"><img width="72" height="48" src="http://www.w3.org/Icons/w3c_home" alt="W3C"></a></p><h1 property="dcterms:title" class="title" id="title">RDF 1.1 Concepts and Abstract Syntax</h1><h2 property="dcterms:issued" datatype="xsd:dateTime" content="2011-08-29T23:00:00+0000" id="w3c-working-draft-30-august-2011">W3C Working Draft 30 August 2011</h2><dl><dt>This version:</dt><dd><a href="http://www.w3.org/TR/2011/WD-rdf11-concepts-20110830/">http://www.w3.org/TR/2011/WD-rdf11-concepts-20110830/</a></dd><dt>Latest published version:</dt><dd><a href="http://www.w3.org/TR/rdf11-concepts/">http://www.w3.org/TR/rdf11-concepts/</a></dd><dt>Latest editor's draft:</dt><dd><a href="http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html">http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html</a></dd><dt>Latest recommendation:</dt><dd><a href="http://www.w3.org/TR/rdf-concepts/">http://www.w3.org/TR/rdf-concepts/</a></dd><dt>Editors:</dt><dd rel="bibo:editor"><span typeof="foaf:Person"><a rel="foaf:homepage" property="foaf:name" content="Richard Cyganiak" href="http://richard.cyganiak.de/">Richard Cyganiak</a>, <a rel="foaf:workplaceHomepage" href="http://www.deri.ie/">DERI, NUI Galway</a></span>
</dd>
<dd rel="bibo:editor"><span typeof="foaf:Person"><span property="foaf:name">David Wood</span>, <a rel="foaf:workplaceHomepage" href="http://www.talis.com/">Talis</a></span>
</dd>
<dt>Previous editors:</dt><dd><span><a content="Graham Klyne" href="http://www.ninebynine.org/">Graham Klyne</a>, Nine by Nine</span>
</dd>
<dd><span><span>Jeremy J. Carroll</span>, Hewlett Packard Labs</span>
</dd>
<dd><span><span>Brian McBride</span>, Hewlett Packard Labs (RDF 2004 Series Editor)</span>
</dd>
</dl><p class="copyright"><a rel="license" href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2004-2011 <span rel="dcterms:publisher"><span typeof="foaf:Organization"><a rel="foaf:homepage" property="foaf:name" content="World Wide Web Consotrium" href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup></span></span> (<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><hr></div>

<div id="abstract" class="introductory section" property="dcterms:abstract" datatype="" typeof="bibo:Chapter" about="#abstract"><h2>Abstract</h2>
    <p>The Resource Description Framework (RDF) is a framework for
    representing information in the Web.</p>
    <p>RDF Concepts and Abstract Syntax defines an abstract syntax
    on which RDF is based, and which serves to link its concrete
    syntax to its formal semantics. It also includes discussion of
    key concepts, datatyping, character normalization
    and handling of IRIs.</p>
</div><div id="sotd" class="introductory section" typeof="bibo:Chapter" about="#sotd"><h2>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 document is work in progress towards a revision of the
  <a href="http://www.w3.org/TR/rdf-concepts/"><em>RDF Concepts
  and Abstract Syntax</em></a> Recommendation,
  and is intended to eventually replace that document.
  It is part of a larger effort to revise the
  <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-Introduction">RDF specifications as published in 2004</a>.
  The most significant changes from the 2004 edition are:
  modified <a href="#section-Graph-Literal">string literals</a>,
  a <a href="#section-skolemization">section on skolemization
  of blank nodes</a>, and many updated
  <a href="#references">references</a> to other specifications
  (including a change in terminology from
  “URI references” to “IRIs”). A fuller list of changes that
  have been made to date is provided in <a href="#changes">Appendix A</a>.
  Various areas of work to be tackled in upcoming
  working drafts are highlighted throughout the document, but
  should not yet be understood as an exhaustive list.</p>
<p>This document was published by the <a href="http://www.w3.org/2011/rdf-wg/">RDF Working Group</a> as a First Public Working Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to <a href="mailto:public-rdf-comments@w3.org">public-rdf-comments@w3.org</a> (<a href="mailto:public-rdf-comments-request@w3.org?subject=subscribe">subscribe</a>, <a href="http://lists.w3.org/Archives/Public/public-rdf-comments/">archives</a>). All feedback is welcome.</p><p>Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.</p><p>This document was produced by a group 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/46168/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group; that page also includes 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 id="toc" typeof="bibo:Chapter" about="#toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#section-Introduction" class="tocxref"><span class="secno">1. </span>Introduction</a></li><li class="tocline"><a href="#conformance" class="tocxref"><span class="secno">2. </span>Conformance</a></li><li class="tocline"><a href="#section-Concepts" class="tocxref"><span class="secno">3. </span>RDF Concepts</a><ul class="toc"><li class="tocline"><a href="#section-data-model" class="tocxref"><span class="secno">3.1 </span>Graph Data Model</a></li><li class="tocline"><a href="#section-IRI-Vocabulary" class="tocxref"><span class="secno">3.2 </span>IRI-based Vocabulary and Node Identification</a></li><li class="tocline"><a href="#section-Datatypes-intro" class="tocxref"><span class="secno">3.3 </span>Datatypes</a></li><li class="tocline"><a href="#section-Literals" class="tocxref"><span class="secno">3.4 </span>Literals</a></li><li class="tocline"><a href="#section-Entailment" class="tocxref"><span class="secno">3.5 </span>Entailment</a></li></ul></li><li class="tocline"><a href="#section-URIspaces" class="tocxref"><span class="secno">4. </span>RDF Vocabulary IRI and Namespace</a></li><li class="tocline"><a href="#section-Datatypes" class="tocxref"><span class="secno">5. </span>Datatypes</a><ul class="toc"><li class="tocline"><a href="#section-XMLLiteral" class="tocxref"><span class="secno">5.1 </span>XML Content within an RDF Graph</a></li></ul></li><li class="tocline"><a href="#section-Graph-syntax" class="tocxref"><span class="secno">6. </span>Abstract Syntax</a><ul class="toc"><li class="tocline"><a href="#section-triples" class="tocxref"><span class="secno">6.1 </span>RDF Triples</a></li><li class="tocline"><a href="#section-rdf-graph" class="tocxref"><span class="secno">6.2 </span>RDF Graph</a></li><li class="tocline"><a href="#section-graph-equality" class="tocxref"><span class="secno">6.3 </span>Graph Equivalence</a></li><li class="tocline"><a href="#section-IRIs" class="tocxref"><span class="secno">6.4 </span>IRIs</a></li><li class="tocline"><a href="#section-Graph-Literal" class="tocxref"><span class="secno">6.5 </span>RDF Literals</a><ul class="toc"><li class="tocline"><a href="#section-Literal-Equality" class="tocxref"><span class="secno">6.5.1 </span>Literal Equality</a></li><li class="tocline"><a href="#section-Literal-Value" class="tocxref"><span class="secno">6.5.2 </span>The Value Corresponding to a Typed Literal</a></li></ul></li><li class="tocline"><a href="#section-blank-nodes" class="tocxref"><span class="secno">6.6 </span>Blank Nodes</a><ul class="toc"><li class="tocline"><a href="#section-skolemization" class="tocxref"><span class="secno">6.6.1 </span>Replacing Blank Nodes with IRIs</a></li></ul></li><li class="tocline"><a href="#section-multigraph" class="tocxref"><span class="secno">6.7 </span>Abstract Syntax for Working with Multiple Graphs</a></li></ul></li><li class="tocline"><a href="#section-fragID" class="tocxref"><span class="secno">7. </span>Fragment Identifiers</a></li><li class="tocline"><a href="#section-Acknowledgments" class="tocxref"><span class="secno">8. </span>Acknowledgments</a></li><li class="tocline"><a href="#changes" class="tocxref"><span class="secno">A. </span>Changes from RDF 2004</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">B. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">B.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">B.2 </span>Informative references</a></li></ul></li></ul></div>





<div id="section-Introduction" typeof="bibo:Chapter" about="#section-Introduction" class="section">
    <!--OddPage--><h2><span class="secno">1. </span>Introduction</h2>

    <p class="issue">This document reflects current progress of the RDF Working
      Group towards updating the
      <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">2004
      version of <em>RDF Concepts and Abstract Syntax</em></a>. The
      editors expect to work on a number of issues, some of which are
      listed in boxes like this throughout the document.</p>

    <p>The Resource Description Framework (RDF) is a framework for
    representing information in the Web.</p>

    <p>This document defines an abstract syntax (a data model)
    on which RDF is based,
    and which serves to link concrete syntaxes to its formal
    semantics. It also includes discussion of
    key concepts, datatyping, character normalization
    and handling of IRIs.</p>

    <p>Normative documentation of RDF falls into the following
    areas:</p>

    <ul>
      <li>Serialization syntaxes (Turtle [<cite><a class="bibref" rel="biblioentry" href="#bib-TURTLE-TR">TURTLE-TR</a></cite>], RDFa [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-PRIMER">RDFA-PRIMER</a></cite>], RDF/XML [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SYNTAX-GRAMMAR">RDF-SYNTAX-GRAMMAR</a></cite>], N-Triples [<cite><a class="bibref" rel="biblioentry" href="#bib-N-TRIPLES">N-TRIPLES</a></cite>]),</li>

      <li>the RDF Vocabulary Description Language ([<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SCHEMA">RDF-SCHEMA</a></cite>]),</li>

      <li>a formal model-theoretic semantics [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-MT">RDF-MT</a></cite>], and</li>

      <li>this document.</li>
    </ul>

    <p>The framework is designed so that vocabularies can be layered.  
    The terms defined in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SCHEMA">RDF-SCHEMA</a></cite>] are the first such vocabulary.
    Several other vocabularies for RDF are
    mentioned in the Primer [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-PRIMER">RDF-PRIMER</a></cite>].</p>
</div>


<div id="conformance" typeof="bibo:Chapter" about="#conformance" class="section"><!--OddPage--><h2><span class="secno">2. </span>Conformance</h2><p>As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.</p>
<p>The key words <em class="rfc2119" title="must">must</em>, <em class="rfc2119" title="must not">must not</em>, <em class="rfc2119" title="required">required</em>, <em class="rfc2119" title="should">should</em>, <em class="rfc2119" title="should not">should not</em>, <em class="rfc2119" title="recommended">recommended</em>, <em class="rfc2119" title="may">may</em>, and <em class="rfc2119" title="optional">optional</em> in this specification are to be interpreted as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC2119">RFC2119</a></cite>].</p>
</div>


<div id="section-Concepts" class="informative section" typeof="bibo:Chapter" about="#section-Concepts">
    <!--OddPage--><h2><span class="secno">3. </span>RDF Concepts</h2><p><em>This section is non-normative.</em></p>

    <p class="issue">This section is quite redundant with later
    normative sections and the RDF Primer. Its removal has been
    proposed. This is
    <a href="http://www.w3.org/2011/rdf-wg/track/issues/68">ISSUE-68</a>.</p>

    <p>RDF uses the following key concepts:</p>

    <ul>
      <li>Graph data model</li>

      <li>IRI-based vocabulary</li>

      <li>Datatypes</li>

      <li>Literals</li>

      <li>Entailment</li>
    </ul>


<div id="section-data-model" typeof="bibo:Chapter" about="#section-data-model" class="section">
    <h3><span class="secno">3.1 </span>Graph Data Model</h3>

    <p>The underlying structure of any expression in RDF is a
    collection of triples, each consisting of a subject, a
    predicate and an object. A set of such triples is called an RDF
    graph (defined more formally in 
<a href="#section-Graph-syntax">section 6</a>). This can be
    illustrated by a node and directed-arc diagram, in which each
    triple is represented as a node-arc-node link (hence the term
    “graph”).</p>

    <div class="figure">
      <img src="Graph-ex.gif" alt="image of the RDF triple comprising (subject, predicate, object)">
    </div>

    <p>Each triple represents a statement of a relationship between
    the things denoted by the nodes that it links. Each triple has
    three parts:</p>
    <ol>
      <li>a <a href="#dfn-subject" class="internalDFN">subject</a>,</li>
      <li>an <a href="#dfn-object" class="internalDFN">object</a>, and</li>
      <li>a <a href="#dfn-predicate" class="internalDFN">predicate</a> (also called a
      <a href="#dfn-property" class="internalDFN">property</a>) that denotes a
      relationship.</li>
    </ol>
    <p>The direction of the arc is significant: it always points
    toward the object.</p>
    <p>The <a title="node" href="#dfn-node" class="internalDFN">nodes</a> of an RDF graph
    are its subjects and objects.</p>
    <p>The assertion of an RDF triple says that some relationship,
    indicated by the predicate, holds between the things denoted by
    subject and object of the triple. The assertion of an RDF graph
    amounts to asserting all the triples in it, so the meaning of
    an RDF graph is the conjunction (logical AND) of the statements
    corresponding to all the triples it contains. A formal account
    of the meaning of RDF graphs is given in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-MT">RDF-MT</a></cite>].</p>
</div>


<div id="section-IRI-Vocabulary" typeof="bibo:Chapter" about="#section-IRI-Vocabulary" class="section">
    <h3><span class="secno">3.2 </span>IRI-based Vocabulary and Node Identification</h3>

    <p>A <a href="#dfn-node" class="internalDFN">node</a> may be an <a href="#dfn-iri" class="internalDFN">IRI</a>, a <a href="#dfn-literal" class="internalDFN">literal</a>,
    or <a title="blank node" href="#dfn-blank-node" class="internalDFN">blank</a> (having no separate form of identification).
    Properties are <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a>.</p>
    <p>An <a href="#dfn-iri" class="internalDFN">IRI</a> or <a href="#dfn-literal" class="internalDFN">literal</a> used as a node identifies what
    that node represents. An IRI used as a predicate
    identifies a relationship between the things represented by the nodes it connects. A
    predicate IRI may also be a node in the graph.</p>
    <p>A <a href="#dfn-blank-node" class="internalDFN">blank node</a> is a node that is
    not an IRI or a literal. In the RDF abstract syntax, a
    blank node is just a unique node that can be used in one or
    more RDF statements.</p>
    <p>A convention used by some linear representations of an RDF
    graph to allow several statements to use the same
    blank node is to use a <dfn id="dfn-blank-node-identifier">blank node
    identifier</dfn>, which is a local identifier that can be
    distinguished from all IRIs and literals. When graphs are
    merged, their blank nodes must be kept distinct if meaning is
    to be preserved; this may call for re-allocation of blank node
    identifiers. Note that such blank node identifiers are not part
    of the RDF abstract syntax, and the representation of triples
    containing blank nodes is entirely dependent on the particular
    concrete syntax used.</p>
</div>


<div id="section-Datatypes-intro" typeof="bibo:Chapter" about="#section-Datatypes-intro" class="section">
    <h3><span class="secno">3.3 </span>Datatypes</h3>

    <p>Datatypes are used by RDF in the representation of values such
    as integers, floating point numbers and dates.</p>

 <p>
A datatype consists of a lexical space, a value space and a lexical-to-value 
mapping, see <a href="#section-Datatypes">section 5</a>.
</p>

    <p>For example, the lexical-to-value mapping for the XML Schema datatype
    <var>xsd:boolean</var>, where each member of the value space
    (represented here as 'T' and 'F') has two lexical representations,
    is as follows:</p>

    <table border="1" cellpadding="5" summary="A table detailing the xsd:boolean datatype.">
      <tbody><tr>
        <th align="left">Value Space</th>

        <td>{T, F}</td>
      </tr>

      <tr>
        <th align="left">Lexical Space</th>

        <td>{"0", "1", "true", "false"}</td>
      </tr>

      <tr>
        <th align="left">Lexical-to-Value Mapping</th>

        <td>{&lt;"true", T&gt;, &lt;"1", T&gt;, &lt;"0", F&gt;,
        &lt;"false", F&gt;}</td>
      </tr>
    </tbody></table>

    <p>RDF predefines just one datatype <code><a href="#dfn-rdf-xmlliteral" class="internalDFN">rdf:XMLLiteral</a></code>, used for
    embedding XML in RDF (see <a href="#section-XMLLiteral">section
    5.1</a>).</p>

    <p>There is no built-in concept of numbers or dates or other common
    values. Rather, RDF defers to datatypes that are defined
    separately, and identified with <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a>.
    The predefined XML Schema
    datatypes [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSCHEMA-2">XMLSCHEMA-2</a></cite>] are expected
    to be widely used for this purpose.</p>


    <p>RDF provides no mechanism for defining new datatypes. XML Schema
    Datatypes [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSCHEMA-2">XMLSCHEMA-2</a></cite>] provides an
    extensibility framework suitable for defining new datatypes for use
    in RDF.</p>
</div>


<div id="section-Literals" typeof="bibo:Chapter" about="#section-Literals" class="section">
    <h3><span class="secno">3.4 </span>Literals</h3>

    <p><a title="literal" href="#dfn-literal" class="internalDFN">Literals</a> are used to identify values such as numbers and dates
    by means of a lexical representation. Anything represented by a
    literal could also be represented by an <a href="#dfn-iri" class="internalDFN">IRI</a>, but it is often more
    convenient or intuitive to use literals.</p>

    <p>A literal may be the object of an RDF statement, but not the
    subject or the predicate.</p>

    <p>Literals may be <cite>typed</cite> or <cite>language-tagged</cite>:</p>

    <ul>
      <li>A <a href="#dfn-typed-literal" class="internalDFN">typed literal</a> is a string combined with a
      <a href="#dfn-datatype-iri" class="internalDFN">datatype IRI</a>. It denotes the
      member of the identified datatype's value space obtained by
      applying the lexical-to-value mapping to the literal string.</li>

      <li>A <a href="#dfn-language-tagged-literal" class="internalDFN">language-tagged literal</a> is a string combined
      with a language tag. This may be used for
      plain text in a natural language. Language-tagged literals
      are self-denoting.</li>
    </ul>

    <p>Continuing the example from <a href="#section-Datatypes-intro">section
    3.3</a>, the typed literals that can be defined using the XML
    Schema datatype <var>xsd:boolean</var> are:</p>

    <table border="1" cellpadding="5" summary="This table lists the literals of type xsd:boolean.">
      <tbody><tr>
        <th>Typed Literal</th>

        <th>Lexical-to-Value Mapping</th>

        <th>Value</th>
      </tr>

      <tr>
        <td align="center">&lt;xsd:boolean, "true"&gt;</td>

        <td align="center">&lt;"true", T&gt;</td>

        <td align="center">T</td>
      </tr>

      <tr>
        <td align="center">&lt;xsd:boolean, "1"&gt;</td>

        <td align="center">&lt;"1", T&gt;</td>

        <td align="center">T</td>
      </tr>

      <tr>
        <td align="center">&lt;xsd:boolean, "false"&gt;</td>

        <td align="center">&lt;"false", F&gt;</td>

        <td align="center">F</td>
      </tr>

      <tr>
        <td align="center">&lt;xsd:boolean, "0"&gt;</td>

        <td align="center">&lt;"0", F&gt;</td>

        <td align="center">F</td>
      </tr>
    </tbody></table>

    <p>For text that may contain 
    markup, use typed literals
with type <a href="#section-XMLLiteral">rdf:XMLLiteral</a>.
If language annotation is required, 
it    must be explicitly included as markup, usually by means of an 
<code>xml:lang</code> attribute. 
XHTML [<cite><a class="bibref" rel="biblioentry" href="#bib-XHTML10">XHTML10</a></cite>] may be included within RDF
in this way. Sometimes, in this latter case, 
 an additional <code>span</code> or <code>div</code> 
    element is needed to carry an
<code>xml:lang</code> or <code>lang</code> attribute. 
    </p>

<p class="issue">Update the XHTML 1.0 reference to something more recent?</p>

<p>
The string in both plain and typed literals is recommended to
be in Unicode Normal Form C [<cite><a class="bibref" rel="biblioentry" href="#bib-NFC">NFC</a></cite>]. This is motivated
by [<cite><a class="bibref" rel="biblioentry" href="#bib-CHARMOD">CHARMOD</a></cite>] particularly 
<a href="http://www.w3.org/TR/2003/WD-charmod-20030822/#sec-Normalization">section 4 
Early Uniform Normalization</a>.
</p>

</div>


<div id="section-Entailment" typeof="bibo:Chapter" about="#section-Entailment" class="section">
    <h3><span class="secno">3.5 </span>Entailment</h3>

    <p>The ideas on meaning and inference in RDF are underpinned by the
    formal concept of <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#entail">
<cite>entailment</cite></a>, as 
      discussed in the RDF
    semantics document [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-MT">RDF-MT</a></cite>].
In brief,  an RDF expression A is said to
<dfn title="entailment" id="dfn-entailment">entail</dfn> another RDF&nbsp;expression B
if every possible
arrangement of things in the world that makes A true also makes B
true. On this basis, if the truth of A is presumed or demonstrated
then the truth of B can be inferred . 
</p>
</div>

</div>


<div id="section-URIspaces" typeof="bibo:Chapter" about="#section-URIspaces" class="section">
    <!--OddPage--><h2><span class="secno">4. </span>RDF Vocabulary IRI and Namespace</h2>

    <p>RDF uses <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a> to identify resources
    and properties. Certain
    IRIs with the following leading substring are defined by the
    RDF specifications to denote specific concepts:</p>

    <ul>
      <li><code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>
      (conventionally associated with namespace prefix <code>rdf:</code>)</li>
    </ul>

    <p>Vocabulary terms in the <code>rdf:</code>
    namespace are listed and described in detail in the
    RDF Schema specification [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SCHEMA">RDF-SCHEMA</a></cite>].</p>

    <p class="note">The RDF namespace is also used as an
    XML namespace [<cite><a class="bibref" rel="biblioentry" href="#bib-XML-NAMES">XML-NAMES</a></cite>] to define a number of additional
    element and attribute names for purely syntactic purposes within
    the RDF/XML syntax ([<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SYNTAX-GRAMMAR">RDF-SYNTAX-GRAMMAR</a></cite>],
    <a href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/#section-Namespace">section 5.1</a>).
    These terms (e.g., <code>rdf:about</code> and <code>rdf:ID</code>)
    do not denote concepts.</p>
</div>


<div id="section-Datatypes" typeof="bibo:Chapter" about="#section-Datatypes" class="section">
   <!--OddPage--><h2><span class="secno">5. </span>Datatypes</h2>

    <p class="issue">This section perhaps should discuss
    <a href="http://www.w3.org/TR/rdf-mt/#dtype_interp">the XSD datatype map</a>
    and <code><a href="http://www.w3.org/TR/rdf-plain-literal/">rdf:PlainLiteral</a></code>.
    This is <a href="http://www.w3.org/2011/rdf-wg/track/issues/70">ISSUE-70</a>.</p>

<p>
The datatype abstraction used in RDF is compatible with 
the abstraction used in
XML Schema Part 2:
    Datatypes [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSCHEMA-2">XMLSCHEMA-2</a></cite>].</p>
<p>
A datatype consists of a lexical space, a value space and a lexical-to-value 
mapping.
</p>
<p>The <dfn id="dfn-lexical-space">lexical space</dfn> of a datatype is a set of Unicode [<cite><a class="bibref" rel="biblioentry" href="#bib-UNICODE">UNICODE</a></cite>] strings.</p>
<p>
The <dfn id="dfn-lexical-to-value-mapping">lexical-to-value mapping</dfn> of a datatype is a set of pairs whose 
first element belongs to 
the <a href="#dfn-lexical-space" class="internalDFN">lexical space</a> of the datatype, 
and the second element belongs to the 
 <dfn id="dfn-value-space">value space</dfn> of the datatype:
</p>
<ul>
<li>
Each member of the lexical space is paired with (maps to) exactly one member 
of the value space.
</li>
<li>
Each member of the value space may be paired with any number (including 
zero) of members of the lexical space (lexical representations for that 
value).
</li>
</ul>
<p>
A datatype is identified by one or more IRIs.
</p>
<p>
RDF may be used with any datatype definition that conforms to this
abstraction, even if not defined in terms of XML Schema.
</p>
   <p>Certain XML Schema built-in datatypes are not suitable for use 
    within RDF. For example, the 
<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#QName">QName</a> 
datatype  requires a namespace declaration to be in scope during
    the mapping, and is not recommended for use in RDF.
    [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-MT">RDF-MT</a></cite>] contains a 
<a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#dtype_interp">more detailed discussion</a>
 of specific XML Schema built-in datatypes. </p>

<div class="note">
<p>When the datatype is defined using XML Schema:
</p>
<ul>
<li>
All values correspond to some lexical form, either using
the lexical-to-value mapping of the datatype or if it is a union
datatype with a lexical mapping associated with one of the member
datatypes.
</li>
<li>
XML Schema facets remain part of the datatype and are used by the XML 
Schema mechanisms that control the lexical space and the value space; 
however, RDF does not define a standard mechanism to access these facets.</li>

<li>In [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSCHEMA-1">XMLSCHEMA-1</a></cite>],
<a href="http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/#section-White-Space-Normalization-during-Validation">
white space normalization</a> occurs
during 
<a href="http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/#key-vn">validation</a> 
according to the value of the 
<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#rf-whiteSpace">whiteSpace
facet</a>. The lexical-to-value mapping used in RDF datatyping
occurs after this, so that the whiteSpace facet has no
effect in RDF datatyping.
</li>
</ul>

</div>


<div id="section-XMLLiteral" typeof="bibo:Chapter" about="#section-XMLLiteral" class="section">
    <h3><span class="secno">5.1 </span>XML Content within an RDF Graph</h3>

    <p class="issue">The canonicalization rules required for XML literals
    are quite complicated. Increasingly, RDF is produced and consumed in
    environments where no XML parser and canonicalization engine is
    available. A possible change to relax the requirements for the
    lexical space, while retaining the value space, is under discussion.
    This is <a href="http://www.w3.org/2011/rdf-wg/track/issues/13">ISSUE-13</a>.</p>

    <p>RDF provides for XML content as a possible literal value.
    Such content is indicated in an RDF graph using a typed literal
    whose datatype is a special built-in datatype
    <dfn id="dfn-rdf-xmlliteral">rdf:XMLLiteral</dfn>,
    defined as follows.</p>

   
    <dl>
      <dt><a name="XMLLiteral-uri" id="XMLLiteral-uri">An IRI for
identifying this datatype</a></dt>

      <dd>is
      <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral</code>.</dd>

      
 

      <dt><a name="XMLLiteral-lexical-space" id="XMLLiteral-lexical-space">The lexical space</a></dt>

<dd>is the set of all
strings:
<ul>
<li>which are well-balanced, self-contained 
<a href="http://www.w3.org/TR/2000/REC-xml-20001006#NT-content">
XML content</a> 
[<cite><a class="bibref" rel="biblioentry" href="#bib-XML10">XML10</a></cite>];
</li>
<li>for which encoding as UTF-8 
[<cite><a class="bibref" rel="biblioentry" href="#bib-UTF-8">UTF-8</a></cite>] yields 
<a href="http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/#def-exclusive-canonical-XML">
exclusive
Canonical XML </a> (with comments, with empty  
<a href="http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/#def-InclusiveNamespaces-PrefixList">
InclusiveNamespaces PrefixList
</a>) [<cite><a class="bibref" rel="biblioentry" href="#bib-XML-EXC-C14N">XML-EXC-C14N</a></cite>];
</li>
<li>for which embedding between an arbitrary XML start tag and an end tag
yields a document conforming to <a href="http://www.w3.org/TR/1999/REC-xml-names-19990114/">XML
      Namespaces</a> [<cite><a class="bibref" rel="biblioentry" href="#bib-XML-NAMES">XML-NAMES</a></cite>]</li>
</ul>
</dd>


   <dt><a name="XMLLiteral-value-space" id="XMLLiteral-value-space">The value space</a></dt>

      <dd>is a set of entities, called XML values, which is:
<ul>
<li>disjoint from the lexical space;</li>
<li>disjoint from the value space of any other datatype that is not explicitly defined as a sub- or supertype of this datatype;</li>
<li>disjoint from the set of Unicode character strings [<cite><a class="bibref" rel="biblioentry" href="#bib-UNICODE">UNICODE</a></cite>];</li>
<li>and in 1:1 correspondence with the lexical space.</li>
</ul>
</dd>

      <dt><a name="XMLLiteral-mapping" id="XMLLiteral-mapping">The lexical-to-value mapping</a></dt>

      <dd>
is a one-one mapping from the lexical space onto the value space,
    i.e. it is both injective and surjective.
</dd> 



    </dl>

      <p class="note">Not all values of this datatype are compliant
      with XML 1.1 [<cite><a class="bibref" rel="biblioentry" href="#bib-XML11">XML11</a></cite>]. If compliance
      with XML 1.1 is desired, then only those values that are
<a href="http://www.w3.org/TR/2002/CR-xml11-20021015/#sec2.13">fully
      normalized</a> according to XML 1.1 should be used.</p>

      <p class="note">XML values can be thought of as the 
[<cite><a class="bibref" rel="biblioentry" href="#bib-XML-INFOSET">XML-INFOSET</a></cite>] or the [<cite><a class="bibref" rel="biblioentry" href="#bib-XPATH">XPATH</a></cite>]
nodeset corresponding to the lexical form, with an appropriate equality
function.</p>

      <p class="note">RDF applications may use additional equivalence relations, such as
that which relates an 
<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#string"><code>xsd:string</code></a>
 
with an <code>rdf:XMLLiteral</code> corresponding to
a single text node of the same string.</p>

</div>

</div>


<div id="section-Graph-syntax" typeof="bibo:Chapter" about="#section-Graph-syntax" class="section">
    <!--OddPage--><h2><span class="secno">6. </span>Abstract Syntax</h2>

    <p>This section defines the RDF abstract syntax. The RDF abstract
    syntax is a set of triples, called the RDF graph.</p>

    <p>This section also defines equivalence between RDF graphs. A
    definition of equivalence is needed to support the RDF Test Cases
    [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-TESTCASES">RDF-TESTCASES</a></cite>] specification.</p>

<p class="note">This <em>abstract</em> syntax is the
syntax over which the formal semantics are defined.
Implementations are free to represent RDF graphs in
any other equivalent form.  As an example:
in an RDF graph,
literals with datatype <tt>rdf:XMLLiteral</tt> can be represented
in a non-canonical
format, and canonicalization performed during the comparison between two
such literals. In this example the comparisons may be
being performed either between syntactic structures or
between their denotations in the domain of discourse.
Implementations that do not require any such comparisons can
hence be optimized.
</p>


<div id="section-triples" typeof="bibo:Chapter" about="#section-triples" class="section">
    <h3><span class="secno">6.1 </span>RDF Triples</h3>

    <p>An <dfn id="dfn-rdf-triple">RDF triple</dfn> contains three components:</p>

    <ul>
      <li>the <dfn id="dfn-subject">subject</dfn>, which is an
      <a href="#dfn-iri" class="internalDFN">IRI</a> or a <a href="#dfn-blank-node" class="internalDFN">blank node</a></li>

      <li>the <dfn id="dfn-predicate">predicate</dfn>, which is an <a href="#dfn-iri" class="internalDFN">IRI</a></li>

      <li>the <dfn id="dfn-object">object</dfn>, which is an <a href="#dfn-iri" class="internalDFN">IRI</a>,
      a <a href="#dfn-literal" class="internalDFN">literal</a> or a <a href="#dfn-blank-node" class="internalDFN">blank node</a></li>
    </ul>

    <p>An RDF triple is conventionally written in the order subject,
    predicate, object.</p>
    
    <p>The predicate is also known as the <dfn id="dfn-property">property</dfn> of the triple.</p>

    <p><a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a>, <a title="blank node" href="#dfn-blank-node" class="internalDFN">blank nodes</a> and
    <a title="literal" href="#dfn-literal" class="internalDFN">literals</a> are collectively known as
    <dfn title="RDF term" id="dfn-rdf-term">RDF terms</dfn>.</p>
</div>


<div id="section-rdf-graph" typeof="bibo:Chapter" about="#section-rdf-graph" class="section">
    <h3><span class="secno">6.2 </span>RDF Graph</h3>

    <p>An <dfn id="dfn-rdf-graph">RDF graph</dfn> is a set of RDF triples.</p>

    <p>The set of <dfn title="node" id="dfn-node">nodes</dfn> of an RDF graph is the set of subjects and objects of
    triples in the graph.</p>
</div>

    
<div id="section-graph-equality" typeof="bibo:Chapter" about="#section-graph-equality" class="section">
    <h3><span class="secno">6.3 </span>Graph Equivalence</h3>

    <p>Two <a title="RDF graph" href="#dfn-rdf-graph" class="internalDFN">RDF graphs</a> <var>G</var> and <var>G'</var> are equivalent if there
    is a bijection <var>M</var> between the sets of nodes of the two graphs,
    such that:</p>

    <ol>
      <li><var>M</var> maps blank nodes to blank nodes.</li>
      <li><var>M(lit)=lit</var> for all <a title="literal" href="#dfn-literal" class="internalDFN">RDF literals</a> <var>lit</var> which
      are nodes of <var>G</var>.</li>

      <li><var>M(uri)=uri</var> for all <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a> <var>uri</var>
      which are nodes of <var>G</var>.</li>

      <li>The triple <var>( s, p, o )</var> is in <var>G</var> if and
      only if the triple <var>( M(s), p, M(o) )</var> is in
      <var>G'</var></li>
    </ol>
    <p>With this definition, <var>M</var> shows how each blank node 
   in <var>G</var> can be replaced with
   a new blank node to give  <var>G'</var>.</p>
</div>
    

<div id="section-IRIs" typeof="bibo:Chapter" about="#section-IRIs" class="section">
    <h3><span class="secno">6.4 </span>IRIs</h3>

    <p>An <dfn title="IRI" id="dfn-iri"><acronym title="Internationalized Resource Identifier">IRI</acronym></dfn>
    (Internationalized Resource Identifier) within an RDF graph
    is a Unicode string [<cite><a class="bibref" rel="biblioentry" href="#bib-UNICODE">UNICODE</a></cite>] that conforms to the syntax
    defined in RFC 3987 [<cite><a class="bibref" rel="biblioentry" href="#bib-IRI">IRI</a></cite>]. IRIs are a generalization of
    <dfn title="URI" id="dfn-uri"><acronym title="Uniform Resource Identifier">URI</acronym>s</dfn>
    [<cite><a class="bibref" rel="biblioentry" href="#bib-URI">URI</a></cite>]. Every absolute URI and URL is an IRI.</p>

    <p>IRIs in the RDF abstract syntax <em class="rfc2119" title="must">must</em> be absolute, and <em class="rfc2119" title="may">may</em>
    contain a fragment identifier.</p>

    <p>Two IRIs are equal if and only if they are equivalent
    under Simple String Comparison according to
    <a href="http://tools.ietf.org/html/rfc3987#section-5.1">section 5.1</a>
    of [<cite><a class="bibref" rel="biblioentry" href="#bib-IRI">IRI</a></cite>]. Further normalization <em class="rfc2119" title="must not">must not</em> be performed when
    comparing IRIs for equality.</p>

    <p class="note">When IRIs are used in operations that are only
    defined for URIs, they must first be converted according to
    the mapping defined in
    <a href="http://tools.ietf.org/html/rfc3987#section-3.1">section 3.1</a>
    of [<cite><a class="bibref" rel="biblioentry" href="#bib-IRI">IRI</a></cite>]. A notable example is retrieval over the HTTP
    protocol. The mapping involves UTF-8 encoding of non-ASCII
    characters, %-encoding of octets not allowed in URIs, and
    Punycode-encoding of domain names.</p>

    <p class="note">Some concrete syntaxes permit relative IRIs
    as a shorthand for absolute IRIs, and define how to resolve
    the relative IRIs against a base IRI.</p>

    <p class="note">Previous versions of RDF used the term
    “<dfn id="dfn-rdf-uri-reference">RDF URI Reference</dfn>” instead of “IRI” and allowed
    additional characters:
    “<code>&lt;</code>”, “<code>&gt;</code>”,
    “<code>{</code>”, “<code>}</code>”,
    “<code>|</code>”, “<code>\</code>”,
    “<code>^</code>”, “<code>`</code>”,
    ‘<code>“</code>’ (double quote), and “<code> </code>” (space).
    In IRIs, these characters must be percent-encoded as
    described in <a href="http://tools.ietf.org/html/rfc3986#section-2.1">section 2.1</a>
    of [<cite><a class="bibref" rel="biblioentry" href="#bib-URI">URI</a></cite>].</p>

    <div class="note">
      <p>Interoperability problems can be avoided by minting
      only IRIs that are normalized according to
      <a href="http://tools.ietf.org/html/rfc3987#section-5">Section 5</a>
      of [<cite><a class="bibref" rel="biblioentry" href="#bib-IRI">IRI</a></cite>]. Non-normalized forms that should be avoided
      include:</p>

      <ul>
        <li>Uppercase characters in scheme names and domain names</li>
        <li>Percent-encoding of characters where it is not
          required by IRI syntax</li>
        <li>Explicitly stated HTTP default port
          (<code>http://example.com:80/</code>);
          <code>http://example.com/</code> is preferrable</li>
        <li>Completely empty path in HTTP IRIs
          (<code>http://example.com</code>);
          <code>http://example.com/</code> is preferrable</li>
        <li>“<code>/./</code>” or “<code>/../</code>” in the path
          component of an IRI</li>
        <li>Lowercase hexadecimal letters within percent-encoding
          triplets (“<code>%3F</code>” is preferable over
          “<code>%3f</code>”)</li>
        <li>Punycode-encoding of Internationalized Domain Names
          in IRIs</li>
        <li>IRIs that are not in Unicode Normalization
          Form C [<cite><a class="bibref" rel="biblioentry" href="#bib-NFC">NFC</a></cite>]</li>
      </ul>
    </div>
</div>


<div id="section-Graph-Literal" typeof="bibo:Chapter" about="#section-Graph-Literal" class="section">
    <h3><span class="secno">6.5 </span>RDF Literals</h3>

    <p class="issue">This section is a major departure from RDF 2004
    as <a title="simple literal" href="#dfn-simple-literal" class="internalDFN">simple literals</a> are now treated
    as syntactic sugar for <code>xsd:string</code>
    <a title="typed literal" href="#dfn-typed-literal" class="internalDFN">typed literals</a>. Further changes
    to RDF's literal design are under consideration:
    <a title="language-tagged literal" href="#dfn-language-tagged-literal" class="internalDFN">Language-tagged literals</a>
    may receive a datatype, and
    <a href="http://www.w3.org/TR/rdf-plain-literal/"><code>rdf:PlainLiteral</code>s</a> [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-PLAINLITERAL">RDF-PLAINLITERAL</a></cite>]
    may be folded into the design somehow. This is
    <a href="http://www.w3.org/2011/rdf-wg/track/issues/71">ISSUE-71</a>.</p>

    <p>A <dfn id="dfn-literal">literal</dfn> in an <a href="#dfn-rdf-graph" class="internalDFN">RDF graph</a> is either a
    <a href="#dfn-typed-literal" class="internalDFN">typed literal</a> or a <a href="#dfn-language-tagged-literal" class="internalDFN">language-tagged literal</a>.</p>

    <p>All literals have a <dfn id="dfn-lexical-form">lexical form</dfn> being a Unicode
    [<cite><a class="bibref" rel="biblioentry" href="#bib-UNICODE">UNICODE</a></cite>] string, which <em class="rfc2119" title="should">should</em> be in Normal Form C [<cite><a class="bibref" rel="biblioentry" href="#bib-NFC">NFC</a></cite>].</p>

    <p><dfn title="language-tagged literal" id="dfn-language-tagged-literal">Language-tagged literals</dfn> have
    a <a href="#dfn-lexical-form" class="internalDFN">lexical form</a> and a non-empty <dfn id="dfn-language-tag">language tag</dfn> as
    defined by [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>]. The language tag <em class="rfc2119" title="must">must</em> be well-formed according to
    <a href="http://tools.ietf.org/html/bcp47#section-2.2.9">section 2.2.9</a>
    of [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>], and <em class="rfc2119" title="must">must</em> be normalized to lowercase.</p>

    <p><dfn title="typed literal" id="dfn-typed-literal">Typed literals</dfn> have a <a href="#dfn-lexical-form" class="internalDFN">lexical form</a>
    and a <dfn id="dfn-datatype-iri">datatype IRI</dfn> being an <a href="#dfn-iri" class="internalDFN">IRI</a>.</p>
 
    <p>Concrete syntaxes <em class="rfc2119" title="may">may</em> support <dfn title="simple literal" id="dfn-simple-literal">simple
    literals</dfn>, consisting of only a <a href="#dfn-lexical-form" class="internalDFN">lexical form</a>
    without any language tag or datatype IRI. Simple literals only
    exist in concrete syntaxes, and are treated as
    syntactic sugar for abstract syntax
    <a title="plain literal" href="#dfn-plain-literal" class="internalDFN">typed literals</a> with the datatype IRI
    <code>http://www.w3.org/2001/XMLSchema#string</code>.
    Simple literals and <a>language-tagged literals</a> are
    collectively known as <dfn title="plain literal" id="dfn-plain-literal">plain literals</dfn>.</p>

    <p class="note">Earlier versions of RDF allowed
    <a title="simple literal" href="#dfn-simple-literal" class="internalDFN">simple literals</a> in the abstract syntax.</p>

      <p class="note">Literals in which the lexical form begins with a
      composing character (as defined by [<cite><a class="bibref" rel="biblioentry" href="#bib-CHARMOD">CHARMOD</a></cite>]) are allowed however they may cause
      interoperability problems, particularly with XML version 1.1 [<cite><a class="bibref" rel="biblioentry" href="#bib-XML11">XML11</a></cite>].</p>

    <p class="note">Earlier versions of RDF permitted tags that
    adhered to the generic tag/subtag syntax of language tags,
    but were not well-formed according to [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>]. Such
    language tags do not conform to RDF 1.1.</p>

      <p class="note">When using the language tag, care must be
      taken not to confuse language with locale. The language
      tag relates only to human language text. Presentational
      issues should
      be addressed in end-user applications.</p>

      <p class="note">The case normalization of 
language tags is part of
 the description of the abstract syntax, and consequently the abstract
 behaviour of RDF applications. It does not constrain an
 RDF implementation to actually normalize the case. Crucially, the result
 of comparing two language tags should not be sensitive to the case of
 the original input.</p>


<div id="section-Literal-Equality" typeof="bibo:Chapter" about="#section-Literal-Equality" class="section">
    <h4><span class="secno">6.5.1 </span>Literal Equality</h4>

    <p>Two literals are equal if and only if all of the following
    hold:</p>

    <ul>
      <li>The strings of the two lexical forms compare equal, character
      by character.</li>

      <li>Either both or neither have language tags.</li>

      <li>The language tags, if any, compare
      equal.</li>

      <li>Either both or neither have datatype IRIs.</li>

      <li>The two datatype IRIs, if any, compare equal, character by
      character.</li>
    </ul>

      <p class="note">RDF Literals are distinct and distinguishable
      from <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a>; e.g. <code>http://example.org/</code> as an RDF
      Literal (untyped, without a language tag) is not equal to
      <code>http://example.org/</code> as an IRI.</p>
</div>


<div id="section-Literal-Value" typeof="bibo:Chapter" about="#section-Literal-Value" class="section">
    <h4><span class="secno">6.5.2 </span>The Value Corresponding to a Typed Literal</h4>

    <p>The datatype IRI refers to a <a href="#section-Datatypes">datatype</a>. For XML Schema <a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#built-in-datatypes">
    built-in</a> datatypes, IRIs such as
    <code>http://www.w3.org/2001/XMLSchema#int</code> are used. The IRI
    of the datatype <a href="#section-XMLLiteral"><tt>rdf:XMLLiteral</tt></a> may be used.
    There may be other, implementation dependent, mechanisms by which
    IRIs refer to datatypes.</p>

    <p>The <em>value</em> associated with a typed literal is found by
    applying the lexical-to-value mapping associated with the datatype IRI to
    the lexical form.
    </p>

    <p>
 If the lexical form is not in
    the lexical space of the datatype associated with the datatype IRI,
then no literal value can be associated with the typed literal.
Such a case, while in error, is not  <em>syntactically</em> ill-formed.</p>
<!--
    <p>A typed literal for which the datatype does not map the lexical
    form to a value is not syntactically ill-formed.</p>
-->
    

      <p class="note">
In application contexts, comparing the values of typed literals (see 
<a href="#section-Literal-Value">
section
6.5.2</a>)
is usually more helpful than comparing their syntactic forms (see 
<a href="#section-Literal-Equality">
section
6.5.1</a>).
Similarly, for comparing RDF Graphs,
semantic notions of entailment (see 
[<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-MT">RDF-MT</a></cite>]) are usually
more helpful than syntactic equality (see 
<a href="#section-graph-equality">
section
6.3</a>).</p>

</div>

</div>


<div id="section-blank-nodes" typeof="bibo:Chapter" about="#section-blank-nodes" class="section">
   <h3><span class="secno">6.6 </span>Blank Nodes</h3>

<p>
The <dfn title="blank node" id="dfn-blank-node">blank nodes</dfn> in an RDF graph 
are drawn from an infinite set.
This set of blank nodes, the set of all <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a>
and the set of all <a title="literal" href="#dfn-literal" class="internalDFN">literals</a> are pairwise disjoint.
</p>
<p>
Otherwise, this set of blank nodes is arbitrary.
</p>
<p>RDF makes no reference to any internal structure of blank nodes.
Given two blank nodes, it is 
possible to determine whether or not they are the same.</p>


<div id="section-skolemization" typeof="bibo:Chapter" about="#section-skolemization" class="section">
    <h4><span class="secno">6.6.1 </span>Replacing Blank Nodes with IRIs</h4>

    <p>Blank nodes do not have identifiers in the RDF abstract syntax. The
    <a title="blank node identifier" href="#dfn-blank-node-identifier" class="internalDFN">blank node identifiers</a> introduced
    by some concrete syntaxes have only
    local scope and are purely an artifact of the serialization.</p>

    <p>In situations where stronger identification is needed, systems <em class="rfc2119" title="may">may</em>
    systematically transform some or all of the blank nodes in an RDF graph
    into IRIs [<cite><a class="bibref" rel="biblioentry" href="#bib-IRI">IRI</a></cite>].  Systems wishing to do this <em class="rfc2119" title="should">should</em> mint a new, globally
    unique IRI (a <dfn id="dfn-skolem-iri">Skolem IRI</dfn>) for each blank node so transformed.</p>

    <p>This transformation does not change the meaning of an RDF graph,
    provided that the Skolem IRIs do not occur anywhere else.</p>

    <p>Systems may wish to mint Skolem IRIs in such a way that they can
    recognize the IRIs as having been introduced solely to replace a blank
    node, and map back to the source blank node where possible.</p>

    <p>Systems that want Skolem IRIs to be recognizable outside of the system
    boundaries <em class="rfc2119" title="should">should</em> use a well-known IRI [<cite><a class="bibref" rel="biblioentry" href="#bib-WELL-KNOWN">WELL-KNOWN</a></cite>] with the registered
    name <code>genid</code>. This is an IRI that uses the HTTP or HTTPS scheme,
    or another scheme that has been specified to use well-known IRIs; and whose
    path component starts with <code>/.well-known/genid/</code>.

    </p><p>For example, the authority responsible for the domain
    <code>example.com</code> could mint the following recognizable Skolem IRI:</p>

    <pre>http://example.com/.well-known/genid/d26a2d0e98334696f4ad70a677abc1f6</pre>

    <p class="issue">IETF registration of the <code>genid</code> name is
    currently in progress.</p>

    <p class="note">RFC 5785 [<cite><a class="bibref" rel="biblioentry" href="#bib-WELL-KNOWN">WELL-KNOWN</a></cite>] only specifies well-known URIs,
    not IRIs. For the purpose of this document, a well-known IRI is any
    IRI that results in a well-known URI after IRI-to-URI mapping [<cite><a class="bibref" rel="biblioentry" href="#bib-IRI">IRI</a></cite>].</p>
</div>

</div>


<div id="section-multigraph" typeof="bibo:Chapter" about="#section-multigraph" class="section">
    <h3><span class="secno">6.7 </span>Abstract Syntax for Working with Multiple Graphs</h3>

    <div class="issue">
        <p>The Working Group will standardize a model and semantics for
        multiple graphs and graphs stores. The
        <a href="http://www.w3.org/2011/01/rdf-wg-charter">charter</a> notes:</p>

        <blockquote>The RDF Community has used the
        term “named graphs” for a number of years in various settings,
        but this term is ambiguous, and often refers to what could rather
        be referred as quoted graphs, graph literals, IRIs for graphs,
        knowledge bases, graph stores, etc. The term “Support for Multiple
        Graphs and Graph Stores” is used as a neutral term in this charter;
        this term is not and should not be considered as definitive.
        The Working Group will have to define the right term(s).</blockquote>

        <p>Progress on the design for this feature is tracked under multiple
        issues:</p>

        <ul>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/5">ISSUE-5: Should we define Graph Literal datatypes?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/14">ISSUE-14: What is a named graph and what should we call it?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/15">ISSUE-15: What is the relationship between the IRI and the triples in a dataset/quad-syntax/etc</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/17">ISSUE-17: How are RDF datasets to be merged?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/22">ISSUE-22: Does multigraph syntax need to support empty graphs?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/28">ISSUE-28: Do we need syntactic nesting of graphs (g-texts) as in N3?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/29">ISSUE-29: Do we support SPARQL's notion of "default graph"?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/30">ISSUE-30: How does SPARQL's notion of RDF dataset relate our notion of multiple graphs?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/32">ISSUE-32: Can we identify both g-boxes and g-snaps?</a></li>
            <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/33">ISSUE-33: Do we provide a way to refer to sub-graphs and/or individual triples?</a></li>
        </ul>
    </div>
</div>

</div>


<div id="section-fragID" class="informative section" typeof="bibo:Chapter" about="#section-fragID">
    <!--OddPage--><h2><span class="secno">7. </span>Fragment Identifiers</h2><p><em>This section is non-normative.</em></p>

    <p class="issue">This section does not address the case where RDF is
    embedded in other document formats, such as in RDFa or when an RDF/XML
    fragment is embedded in SVG. It has been suggested that this may be
    a general issue for the TAG about the treatment of
    fragment identifiers when one language is embedded in another. This is
    <a href="http://www.w3.org/2011/rdf-wg/track/issues/37">ISSUE-37</a>.</p>

    <p class="issue">This section treats the RDF/XML media type as
    canonical for establishing the referent of IRIs that include
    fragment identifier. Today we have many different media types
    that can carry RDF graphs, and HTTP content negotiation is more
    common. Also, the problem addressed in the section
    (context-dependence of fragment identifiers) has to some extent
    gone away when RFC 2396 was replaced by RFC 3986. The latter
    states that the same fragment should be used for the same thing
    in resources that have multiple representations
    (Section 3.5 [<cite><a class="bibref" rel="biblioentry" href="#bib-URI">URI</a></cite>]). This is
    <a href="http://www.w3.org/2011/rdf-wg/track/issues/69">ISSUE-69</a>.</p>

    <p>RDF uses <a title="IRI" href="#dfn-iri" class="internalDFN">IRIs</a>,
    which may include fragment identifiers, as
    context free identifiers for resources. RFC 2396 states
    that the meaning of a fragment
    identifier depends on the MIME content-type of a document, i.e.
    is context dependent.</p>
    <p>These apparently conflicting views are reconciled by
    considering that an <a href="#dfn-iri" class="internalDFN">IRI</a> in an RDF graph is treated
    with respect to the MIME type <code>application/rdf+xml</code>
    [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-MIME-TYPE">RDF-MIME-TYPE</a></cite>]. Given an IRI that includes a fragment identifier,
    the fragment identifer identifies the same thing
    that it does in an <code>application/rdf+xml</code> representation of the
    resource identified by the IRI excluding the fragment identifier. Thus:</p>
    <ul>
      <li>we assume that the IRI excluding fragment
      identifier identifies a resource, which is presumed to have
      an RDF representation. So when <code>eg:someurl#frag</code> is used in an RDF
      document, <code>eg:someurl</code> is taken to
      designate some RDF document (even when no such document can
      be retrieved).</li>
      <li><code>eg:someurl#frag</code> means the thing
      that is indicated, according to the rules of the
      <code>application/rdf+xml</code> MIME content-type as
      a “fragment” or “view” of the RDF document at
      <code>eg:someurl</code>. If the document does not
      exist, or cannot be retrieved, or is available only in
      formats other than <code>application/rdf+xml</code>, then exactly what
      that view may be is somewhat undetermined, but that does not
      prevent use of RDF to say things about it.</li>
      <li>the RDF treatment of a fragment identifier allows it to
      indicate a thing that is entirely external to the document,
      or even to the “shared information space” known as the Web.
      That is, it can be a more general idea, like some particular
      car or a mythical Unicorn.</li>
      <li>in this way, an <code>application/rdf+xml</code> document acts as an
      intermediary between some Web retrievable documents (itself,
      at least, also any other Web retrievable IRIs that it may
      use, possibly including schema IRIs and references to other
      RDF documents), and some set of possibly abstract or non-Web
      entities that the RDF may describe.</li>
    </ul>
    <p>This provides a handling of IRIs and their
    denotation that is consistent with the RDF model theory and
    usage, and also with conventional Web behavior. Note that
    nothing here requires that an RDF application be able to
    retrieve any representation of resources identified by the IRIs
    in an RDF graph.</p>
</div>


<div id="section-Acknowledgments" class="informative section" typeof="bibo:Chapter" about="#section-Acknowledgments">
    <!--OddPage--><h2><span class="secno">8. </span>Acknowledgments</h2><p><em>This section is non-normative.</em></p>

    <p class="issue">This section does not yet list those who made
    contributions to the RDF 1.1 version, nor does it list the
    current RDF WG members.</p>

    <p>The RDF 2004 editors acknowledge valuable contributions from
    Frank Manola, Pat Hayes, Dan Brickley, Jos de Roo, 
    Dave Beckett, Patrick Stickler, Peter F. Patel-Schneider, Jerome Euzenat, 
    Massimo Marchiori, Tim Berners-Lee, Dave Reynolds and Dan Connolly.</p>

    <p>This specification contains a significant contribution from the
    designers of the RDF typed literal mechanism, Pat
    Hayes, Sergey Melnik and Patrick Stickler. The document draws upon an earlier
    RDF Model and Syntax document edited by Ora Lassilla and Ralph Swick,
    and RDF Schema edited by Dan Brickley and R. V. Guha.</p>

    <p>This specification is a product of extended deliberations by the
    <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-Acknowledgments">members
    of the RDFcore Working Group and the RDF and RDF Schema Working Group</a>.</p>
</div>


<div class="appendix informative section" id="changes" typeof="bibo:Chapter" about="#changes">
  <!--OddPage--><h2><span class="secno">A. </span>Changes from RDF 2004</h2><p><em>This section is non-normative.</em></p>

  <ul>
    <li>2011-08-13: Updated Turtle reference to Turtle FPWD</li>
    <li>2011-07-21: Condensed the 2004 acknowledgements</li>
    <li>2011-07-21: Updated the two sections on literals to reflect the <a href="">ISSUE-12 resolution</a> that simple literals are no longer part of the abstract syntax. Formally introduced the terms “language-tagged literal”, “simple literal”.</li>
    <li>2011-07-21: Updated the introduction, and removed many mentions of RDF/XML. Changed the normative reference for the terms in the RDF namespace from the RDF/XML spec to the RDF Schema spec. Removed any mention of the 1999 version of RDF.</li>
    <li>2011-07-21: Replaced RFC 2279 reference (UTF-8) with RFC 3629</li>
    <li>2011-07-20: Removed informative sections “Motivations and Goals” (see <a href="http://www.w3.org/TR/rdf-concepts/#section-Overview">RDF 2004 version</a>) and “RDF Expression of Simple Facts” (see <a href="http://www.w3.org/TR/rdf-concepts/#section-SimpleFacts">RDF 2004 version</a>)</li>
    <li>2011-06-01: Replaced the URI References section with <a href="#section-IRIs">new section on IRIs</a>, and changed “RDF URI Reference” to “IRI” throughout the document.</li>
    <li>2011-06-01: Changed language tag definition to require well-formedness according to BCP47; added a note that this invalidates some RDF</li>
    <li>2011-05-25: Added boxes for known WG issues throught the document</li>
    <li>2011-05-25: Deleted “Structure of this Document” section, it added no value beyond the TOC</li>
    <li>2011-05-25: Implemented resolution of <a href="http://www.w3.org/2011/rdf-wg/track/issues/40">ISSUE-40: Skolemization advice in the RDF dcocument</a> by adding a section on <a href="#section-skolemization">Replacing Blank Nodes with IRIs</a></li>
    <li>2011-05-25: rdf:XMLLiteral is disjoint from any datatype not explicitly related to it, per erratum <a href="http://www.w3.org/2001/sw/RDFCore/errata#concept-xmlliteral">[concept-xmlliteral]</a></li>
    <li>2011-05-25: Added Conformance section with RFC2119 reference</li>
    <li>2011-05-25: Updated all W3C references to latest editions, and Unicode from v3 to v4</li>
    <li>2011-05-24: Converted to ReSpec, changed metadata to reflect RDF 1.1</li>
  </ul>
</div>




  


<div id="references" class="appendix section" typeof="bibo:Chapter" about="#references"><!--OddPage--><h2><span class="secno">B. </span>References</h2><div id="normative-references" typeof="bibo:Chapter" about="#normative-references" class="section"><h3><span class="secno">B.1 </span>Normative references</h3><dl class="bibliography" about=""><dt id="bib-BCP47">[BCP47]</dt><dd rel="dcterms:requires">A. Phillips; M. Davis. <a href="http://tools.ietf.org/html/bcp47"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href="http://tools.ietf.org/html/bcp47">http://tools.ietf.org/html/bcp47</a> 
</dd><dt id="bib-IRI">[IRI]</dt><dd rel="dcterms:requires">M. Duerst, M. Suignard. <a href="http://www.ietf.org/rfc/rfc3987.txt"><cite>Internationalized Resource Identifiers (IRI).</cite></a> January 2005. Internet RFC 3987. URL: <a href="http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3987.txt</a> 
</dd><dt id="bib-NFC">[NFC]</dt><dd rel="dcterms:requires">M. Davis, Ken Whistler. <a href="http://www.unicode.org/reports/tr15/"><cite>TR15, Unicode Normalization Forms.</cite></a>. 17 September 2010, URL: <a href="http://www.unicode.org/reports/tr15/">http://www.unicode.org/reports/tr15/</a>
</dd><dt id="bib-RDF-MT">[RDF-MT]</dt><dd rel="dcterms:requires">Patrick Hayes. <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210"><cite>RDF Semantics.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210">http://www.w3.org/TR/2004/REC-rdf-mt-20040210</a> 
</dd><dt id="bib-RDF-SCHEMA">[RDF-SCHEMA]</dt><dd rel="dcterms:requires">Dan Brickley; Ramanathan V. Guha. <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210"><cite>RDF Vocabulary Description Language 1.0: RDF Schema.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210">http://www.w3.org/TR/2004/REC-rdf-schema-20040210</a> 
</dd><dt id="bib-RFC2119">[RFC2119]</dt><dd rel="dcterms:requires">S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key words for use in RFCs to Indicate Requirement Levels.</cite></a> March 1997. Internet RFC 2119.  URL: <a href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a> 
</dd><dt id="bib-UNICODE">[UNICODE]</dt><dd rel="dcterms:requires">The Unicode Consortium. <a href="http://www.unicode.org/unicode/standard/versions/enumeratedversions.html"><cite>The Unicode Standard.</cite></a> 2003. Defined by: The Unicode Standard, Version 4.0 (Boston, MA, Addison-Wesley, ISBN 0-321-18578-1), as updated from time to time by the publication of new versions URL: <a href="http://www.unicode.org/unicode/standard/versions/enumeratedversions.html">http://www.unicode.org/unicode/standard/versions/enumeratedversions.html</a> 
</dd><dt id="bib-UTF-8">[UTF-8]</dt><dd rel="dcterms:requires">F. Yergeau. <a href="http://www.ietf.org/rfc/rfc3629.txt"><cite>UTF-8, a transformation format of ISO 10646</cite></a>. IETF RFC 3629. November 2003. URL: <a href="http://www.ietf.org/rfc/rfc3629.txt">http://www.ietf.org/rfc/rfc3629.txt</a>
</dd><dt id="bib-XML-EXC-C14N">[XML-EXC-C14N]</dt><dd rel="dcterms:requires">Donald E. Eastlake 3rd; Joseph Reagle; John Boyer. <a href="http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/"><cite>Exclusive XML Canonicalization Version 1.0.</cite></a> 18 July 2002. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/">http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/</a> 
</dd><dt id="bib-XML-NAMES">[XML-NAMES]</dt><dd rel="dcterms:requires">Richard Tobin; et al. <a href="http://www.w3.org/TR/2009/REC-xml-names-20091208/"><cite>Namespaces in XML 1.0 (Third Edition).</cite></a> 8 December 2009. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2009/REC-xml-names-20091208/">http://www.w3.org/TR/2009/REC-xml-names-20091208/</a> 
</dd><dt id="bib-XML10">[XML10]</dt><dd rel="dcterms:requires">C. M. Sperberg-McQueen; et al. <a href="http://www.w3.org/TR/2008/REC-xml-20081126/"><cite>Extensible Markup Language (XML) 1.0 (Fifth Edition).</cite></a> 26 November 2008. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2008/REC-xml-20081126/">http://www.w3.org/TR/2008/REC-xml-20081126/</a> 
</dd><dt id="bib-XMLSCHEMA-2">[XMLSCHEMA-2]</dt><dd rel="dcterms:requires">Paul V. Biron; Ashok Malhotra. <a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/"><cite>XML Schema Part 2: Datatypes Second Edition.</cite></a> 28 October 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/">http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/</a> 
</dd></dl></div><div id="informative-references" typeof="bibo:Chapter" about="#informative-references" class="section"><h3><span class="secno">B.2 </span>Informative references</h3><dl class="bibliography" about=""><dt id="bib-CHARMOD">[CHARMOD]</dt><dd rel="dcterms:references">Martin J. Dürst; et al. <a href="http://www.w3.org/TR/2005/REC-charmod-20050215"><cite>Character Model for the World Wide Web 1.0: Fundamentals.</cite></a> 15 February 2005. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2005/REC-charmod-20050215">http://www.w3.org/TR/2005/REC-charmod-20050215</a> 
</dd><dt id="bib-N-TRIPLES">[N-TRIPLES]</dt><dd rel="dcterms:references">Jan Grant; Dave Beckett. <a href="http://www.w3.org/TR/rdf-testcases/#ntriples"><cite>N-Triples</cite></a> 10 February 2004. W3C Recommendation. URL:  <a href="http://www.w3.org/TR/rdf-testcases/#ntriples">http://www.w3.org/TR/rdf-testcases/#ntriples</a>
</dd><dt id="bib-RDF-MIME-TYPE">[RDF-MIME-TYPE]</dt><dd rel="dcterms:references"><a href="http://www.iana.org/assignments/media-types/"><cite>MIME Media Types</cite></a>, The Internet Assigned Numbers Authority (IANA). This document is http://www.iana.org/assignments/media-types/ .  The <a href="http://www.w3.org/2001/sw/RDFCore/mediatype-registration">registration for <code>application/rdf+xml</code></a> is archived at http://www.w3.org/2001/sw/RDFCore/mediatype-registration .
</dd><dt id="bib-RDF-PLAINLITERAL">[RDF-PLAINLITERAL]</dt><dd rel="dcterms:references">Jie Bao; Sandro Hawke; Boris Motik; Peter F. Patel-Schneider; Axel Polleres. <a href="http://www.w3.org/TR/2009/REC-rdf-plain-literal-20091027/"><cite>rdf:PlainLiteral: A Datatype for RDF Plain Literals.</cite></a> 27 October 2009. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2009/REC-rdf-plain-literal-20091027/">http://www.w3.org/TR/2009/REC-rdf-plain-literal-20091027/</a>
</dd><dt id="bib-RDF-PRIMER">[RDF-PRIMER]</dt><dd rel="dcterms:references">Frank Manola; Eric Miller. <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/"><cite>RDF Primer.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">http://www.w3.org/TR/2004/REC-rdf-primer-20040210/</a> 
</dd><dt id="bib-RDF-SYNTAX-GRAMMAR">[RDF-SYNTAX-GRAMMAR]</dt><dd rel="dcterms:references">Dave Beckett. <a href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210"><cite>RDF/XML Syntax Specification (Revised).</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210">http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210</a> 
</dd><dt id="bib-RDF-TESTCASES">[RDF-TESTCASES]</dt><dd rel="dcterms:references">Jan Grant; Dave Beckett. <a href="http://www.w3.org/TR/2004/REC-rdf-testcases-20040210"><cite>RDF Test Cases.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-testcases-20040210">http://www.w3.org/TR/2004/REC-rdf-testcases-20040210</a> 
</dd><dt id="bib-RDFA-PRIMER">[RDFA-PRIMER]</dt><dd rel="dcterms:references">Mark Birbeck; Ben Adida. <a href="http://www.w3.org/TR/2008/NOTE-xhtml-rdfa-primer-20081014"><cite>RDFa Primer.</cite></a> 14 October 2008. W3C Note. URL: <a href="http://www.w3.org/TR/2008/NOTE-xhtml-rdfa-primer-20081014">http://www.w3.org/TR/2008/NOTE-xhtml-rdfa-primer-20081014</a> 
</dd><dt id="bib-TURTLE-TR">[TURTLE-TR]</dt><dd rel="dcterms:references">Eric Prud'hommeaux, Gavin Carothers. <a href="http://www.w3.org/TR/2011/WD-turtle-20110809/"><cite>Turtle: Terse RDF Triple Language.</cite></a> 09 August 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-turtle-20110809/">http://www.w3.org/TR/2011/WD-turtle-20110809/</a>
</dd><dt id="bib-URI">[URI]</dt><dd rel="dcterms:references">T. Berners-Lee; R. Fielding; L. Masinter. <a href="http://www.ietf.org/rfc/rfc3986.txt"><cite>Uniform Resource Identifiers (URI): generic syntax.</cite></a> January 2005. Internet RFC 3986. URL: <a href="http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3986.txt</a> 
</dd><dt id="bib-WELL-KNOWN">[WELL-KNOWN]</dt><dd rel="dcterms:references">M. Nottingham; E. Hammer-Lahav. <a href="http://tools.ietf.org/html/rfc5785"><cite>Defining Well-Known Uniform Resource Identifiers (URIs).</cite></a> April 2010. Internet RFC 5785. URL: <a href="http://tools.ietf.org/html/rfc5785">http://tools.ietf.org/html/rfc5785</a>
</dd><dt id="bib-XHTML10">[XHTML10]</dt><dd rel="dcterms:references">Steven Pemberton. <a href="http://www.w3.org/TR/2002/REC-xhtml1-20020801/"><cite>XHTML™ 1.0 The Extensible HyperText Markup Language (Second Edition).</cite></a> 1 August 2002. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2002/REC-xhtml1-20020801/">http://www.w3.org/TR/2002/REC-xhtml1-20020801/</a> 
</dd><dt id="bib-XML-INFOSET">[XML-INFOSET]</dt><dd rel="dcterms:references">John Cowan; Richard Tobin. <a href="http://www.w3.org/TR/2004/REC-xml-infoset-20040204/"><cite>XML Information Set (Second Edition).</cite></a> 4 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-xml-infoset-20040204/">http://www.w3.org/TR/2004/REC-xml-infoset-20040204/</a> 
</dd><dt id="bib-XML11">[XML11]</dt><dd rel="dcterms:references">Eve Maler; et al. <a href="http://www.w3.org/TR/2006/REC-xml11-20060816"><cite>Extensible Markup Language (XML) 1.1 (Second Edition).</cite></a> 16 August 2006. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2006/REC-xml11-20060816">http://www.w3.org/TR/2006/REC-xml11-20060816</a> 
</dd><dt id="bib-XMLSCHEMA-1">[XMLSCHEMA-1]</dt><dd rel="dcterms:references">Henry S. Thompson; et al. <a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/"><cite>XML Schema Part 1: Structures Second Edition.</cite></a> 28 October 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/">http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/</a> 
</dd><dt id="bib-XPATH">[XPATH]</dt><dd rel="dcterms:references">James Clark; Steven DeRose. <a href="http://www.w3.org/TR/1999/REC-xpath-19991116/"><cite>XML Path Language (XPath) Version 1.0.</cite></a> 16 November 1999. W3C Recommendation. URL: <a href="http://www.w3.org/TR/1999/REC-xpath-19991116/">http://www.w3.org/TR/1999/REC-xpath-19991116/</a> 
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