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      "W3C" src="http://www.w3.org/Icons/w3c_home" /></a>

      <h1 id="title">Resource Description Framework (RDF):<br />
       Concepts and Abstract Syntax</h1>

      <h2 id="doctype">W3C Recommendation 10 February 2004</h2>


      <dl>
        <dt>This version:</dt>

        <dd><a href=
        "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">
http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/</a></dd>

        <dt>Latest version:</dt>

        <dd><a href=
        "http://www.w3.org/TR/rdf-concepts/">http://www.w3.org/TR/rdf-concepts/</a></dd>

        <dt>Previous version:</dt>

       <dd><a href=
        "http://www.w3.org/TR/2003/PR-rdf-concepts-20031215/">http://www.w3.org/TR/2003/PR-rdf-concepts-20031215/</a></dd>

        <dt>Editors:</dt>

        <dd><a href="http://www.ninebynine.org/">Graham Klyne</a> (Nine
        by Nine), &lt;<a href=
        "mailto:GK@NineByNine.org">gk@ninebynine.org</a>&gt;</dd>

        <dd><a href="http://www-uk.hpl.hp.com/people/jjc/">Jeremy J.
        Carroll</a> (Hewlett Packard Labs), &lt;<a href=
        "mailto:jjc@hpl.hp.com">jjc@hpl.hp.com</a>&gt;</dd>

        <dt>Series editor:</dt>

        <dd><a href="http://www-uk.hpl.hp.com/people/bwm/">Brian
        McBride</a> (Hewlett Packard Labs) &lt;<a href=
        "mailto:bwm@hplb.hpl.hp.com">bwm@hplb.hpl.hp.com</a>&gt;</dd>
      </dl>


<p>Please refer to the <a
href="http://www.w3.org/2001/sw/RDFCore/errata#rdf-concepts"><strong>errata</strong></a>
for this document, which may include some normative corrections.</p>

<p>See also <a href="http://www.w3.org/2001/sw/RDFCore/translation/rdf-concepts">translations</a>.</p>

<p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">  Copyright</a> &#xa9; 2004 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>&#xae;</sup>  (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.org/"><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>, <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-software">software licensing</a> rules apply.</p>

      <hr title="Separator for header" />
    </div>

    <h2 class="nonum"><a id="abstract" name=
    "abstract">Abstract</a></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
    design goals, key concepts, datatyping, character normalization
    and handling of URI references.</p>

<div class="status">

<h2 class="nonum">
<a id="status" name="status">Status of this Document</a>
</h2>
<!-- Start Status-Of-This-Document Text -->

<p>This document has been reviewed by W3C Members and other interested
parties, and it has been endorsed by the Director as a <a
href="http://www.w3.org/2003/06/Process-20030618/tr.html#RecsW3C">W3C
Recommendation</a>.  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>This is one document in a <a
href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-Introduction">set
of six</a> (<a
href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">Primer</a>,
<a
href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">Concepts</a>,
<a
href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/">Syntax</a>,
<a
href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/">Semantics</a>,
<a
href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210/">Vocabulary</a>,
and <a
href="http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/">Test
Cases</a>) intended to jointly replace the original Resource
Description Framework specifications, <a
href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/">RDF Model and Syntax (1999
Recommendation)</a> and <a
href="http://www.w3.org/TR/2000/CR-rdf-schema-20000327/">RDF Schema
(2000 Candidate Recommendation)</a>.  It has been developed by the <a
href="http://www.w3.org/2001/sw/RDFCore/">RDF Core Working Group</a>
as part of the <a href="http://www.w3.org/2001/sw/">W3C Semantic Web
Activity</a> (<a href="http://www.w3.org/2001/sw/Activity">Activity
Statement</a>, <a
href="http://www.w3.org/2002/11/swv2/charters/RDFCoreWGCharter">Group
Charter</a>) for publication on 10 February 2004.
</p>

<p>Changes to this document since the <a
href="http://www.w3.org/TR/2003/PR-rdf-concepts-20031215/"
shape="rect">Proposed Recommendation Working Draft</a> are detailed in
the <a href="#changes" shape="rect">change log</a>.  </p>

<p> The public is invited to send comments to <a
href="mailto:www-rdf-comments@w3.org">www-rdf-comments@w3.org</a> (<a
href="http://lists.w3.org/Archives/Public/www-rdf-comments/">archive</a>)
and to participate in general discussion of related technology on <a
href="mailto:www-rdf-interest@w3.org"
shape="rect">www-rdf-interest@w3.org</a> (<a
href="http://lists.w3.org/Archives/Public/www-rdf-interest/"
shape="rect">archive</a>).  </p>

<p>A list of <a href="http://www.w3.org/2001/sw/RDFCore/impls">
implementations</a> is available.</p>

<p>The W3C maintains a list of <a href="http://www.w3.org/2001/sw/RDFCore/ipr-statements"
rel="disclosure">any patent disclosures related to this work</a>.</p>

<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>

<!-- End Status-Of-This-Document Text -->

</div>


    <div class="toc">
      <h2 class="nonum"><a id="contents" name="contents">Table of
      Contents</a></h2>

      <ul class="toc">
        <li class="tocline">
          <a href="#section-Introduction"><strong>1.
          Introduction</strong></a>

          <ul class="toc">
            <li class="tocline"><a href="#section-Structure">1.1
            Structure of this Document</a></li>

          </ul>
        </li>

        <li class="tocline">
          <a href="#section-Overview"><strong>2. Motivations and Goals</strong></a>

          <ul class="toc">
            <li class="tocline"><a href="#section-motivation">2.1
            Motivation</a></li>

            <li class="tocline">
              <a href="#section-design-goals">2.2 Design Goals</a>

              <ul class="toc">
                <li class="tocline"><a href="#section-simple-data-model">2.2.1 A
                Simple Data Model</a></li>

                <li class="tocline"><a href="#section-formal-semantics">2.2.2 Formal
                Semantics and Inference</a></li>

                <li class="tocline"><a href="#section-extensible-vocab">2.2.3
                Extensible URI-based Vocabulary</a></li>

                <li class="tocline"><a href="#section-xml-serialization">2.2.4
                XML-based Syntax</a></li>

                <li class="tocline"><a href="#section-use-xsd">2.2.5 Use
                XML Schema Datatypes</a></li>

                <li class="tocline"><a href="#section-anyone">2.2.6 Anyone
                Can Make Statments About Any Resource</a></li>

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

            <li class="tocline">
              <a href="#section-Concepts"><strong>3. RDF Concepts</strong></a>

              <ul class="toc">
                <li class="tocline"><a href="#section-data-model">3.1 Graph
                Data Model</a></li>

                <li class="tocline"><a href=
                "#section-URI-Vocabulary">3.2 URI-based Vocabulary
                and Node Identification</a></li>

                <li class="tocline"><a href="#section-Datatypes-intro">3.3
                Datatypes</a></li>

                <li class="tocline"><a href="#section-Literals">3.4
                Literals</a></li>


                <li class="tocline"><a href=
                "#section-SimpleFacts">3.5 RDF Expression of Simple
                Facts</a></li>

                <li class="tocline"><a href="#section-Entailment">3.6
                Entailment</a></li>
              </ul>
            </li>
            <li class="tocline"><a href="#section-URIspaces"><strong>4. RDF
    Vocabulary URI and Namespace (Normative)</strong></a></li>
        <li class="tocline">
          <a href="#section-Datatypes"><strong>5. Datatypes (Normative)</strong></a>

          <ul class="toc">
        <li class="tocline"><a href="#section-XMLLiteral">5.1
        XML Content within an RDF Graph</a></li>
          </ul>
       </li>

        <li class="tocline">
          <a href="#section-Graph-syntax"><strong>6. Abstract
          Syntax (Normative)</strong></a>

          <ul class="toc">
            <li class="tocline"><a href="#section-triples">6.1 RDF
            Triples</a></li>

            <li class="tocline"><a href="#section-rdf-graph">6.2 RDF
            Graph</a></li>

            <li class="tocline"><a href="#section-graph-equality">6.3 Graph
            Equivalence</a></li>

            <li class="tocline"><a href="#section-Graph-URIref">6.4 RDF
            URI References</a></li>

            <li class="tocline">
              <a href="#section-Graph-Literal">6.5 RDF Literals</a>

              <ul class="toc">
                <li class="tocline"><a href=
                "#section-Literal-Equality">6.5.1 Literal
                Equality</a></li>

                <li class="tocline"><a href=
                "#section-Literal-Value">6.5.2 The Value Corresponding
                to a Typed Literal</a></li>
              </ul>
            </li>

            <li class="tocline"><a href="#section-blank-nodes">6.6 Blank Nodes</a></li>
          </ul>
        </li>

        <li class="tocline">
          <a href="#section-fragID"><strong>7. Fragment Identifiers
</strong></a>
        </li>

        <li class="tocline"><a href=
        "#section-Acknowledgments"><strong>8.
        Acknowledgments</strong></a></li>

        <li class="tocline">
          <a href="#section-References"><strong>9.
          References</strong></a>

          <ul class="toc">
            <li class="tocline"><a href=
            "#section-Normative-References">9.1 Normative
            References</a></li>

            <li class="tocline"><a href=
            "#section-Informative-References">9.2 Informational
            References</a></li>
          </ul>
        </li>

 <li class="tocline">
          <a href="#section-Revisions"><strong>A: Revisions Since Last Call Working Draft of 10 October 2003</strong></a>

        </li>
      </ul>

    </div>
    <hr />

    <h2><a id="section-Introduction" name="section-Introduction">1.
    Introduction</a></h2>

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

    <p>This document defines an abstract syntax on which RDF is based,
    and which serves to link its concrete syntax to its formal
    semantics.
This abstract syntax is quite distinct from XML's tree-based infoset [<a
    href="#ref-xml-infoset">XML-INFOSET</a>]. It also includes discussion of design goals,
    key concepts, datatyping, character normalization
    and handling of URI references.</p>

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

    <ul>
      <li>XML serialization syntax [<a href=
      "#ref-rdf-syntax">RDF-SYNTAX</a>],</li>

      <li>formal semantics [<a href=
      "#ref-rdf-semantics">RDF-SEMANTICS</a>], and</li>

      <li>this document, (sections 4, 5 and 6).</li>
    </ul>

    <p>Within this document, normative sections are explicitly labelled as such.
Explicit notes are informative.</p>

    <p>The framework is designed so that vocabularies can be layered.
The RDF and RDF vocabulary definition (RDF schema)
languages
    [<a href="#ref-rdf-vocabulary">RDF-VOCABULARY</a>] are the first
    such vocabularies.

    Others (cf. OWL [<a href="#ref-owl">OWL</a>] and
    the applications mentioned in the primer
    [<a href=
    "#ref-rdf-primer">RDF-PRIMER</a>]) are in development.</p>

    <h3><a id="section-Structure" name="section-Structure">1.1
    Structure of this Document</a></h3>

    <p>In <a href="#section-Overview">section 2</a>,
the background rationale and design goals
are introduced.
Key concepts follow in <a href="#section-Concepts">section 3</a>.
<a href="#section-URIspaces">Section 4</a> discusses URI references
reserved for use by RDF.
</p>


    <p><a href="#section-Datatypes">Section 5</a> discusses datatypes.
XML content of
    literals is described in <a href="#section-XMLLiteral">section
    5.1</a>, and the abstract syntax is defined in <a href=
    "#section-Graph-syntax">section 6</a> of this document.</p>

    <p><a href="#section-fragID">Section 7</a> discusses the role of fragment
    identifiers in URI references used with RDF.</p>

    <h2><a id="section-Overview" name="section-Overview">2. Motivations and Goals</a></h2>

    <p>RDF has an abstract syntax that reflects a simple graph-based
    data model, and formal semantics with a rigorously defined notion
    of entailment providing a basis for well founded deductions in RDF
    data.</p>

    <h3><a id="section-motivation" name="section-motivation">2.1 Motivation</a></h3>

    <p>The development of RDF has been motivated by the following uses,
    among others:</p>

    <ul>
      <li>Web metadata: providing information about Web resources and
      the systems that use them (e.g. content rating, capability
      descriptions, privacy preferences, etc.)</li>

      <li>Applications that require open rather than constrained
      information models (e.g. scheduling activities, describing
      organizational processes, annotation of Web resources, etc.)</li>

      <li>To do for machine processable information (application data)
      what the World Wide Web has done for hypertext: to allow data to
      be processed outside the particular environment in which it was
      created, in a fashion that can work at Internet scale.</li>

      <li>Interworking among applications: combining data from several
      applications to arrive at new information.</li>

      <li>Automated processing of Web information by software agents:
      the Web is moving from having just human-readable information to
      being a world-wide network of cooperating processes. RDF provides
      a world-wide lingua franca for these processes.</li>
    </ul>

    <p>RDF is designed to represent information in a minimally
    constraining, flexible way. It can be used in isolated
    applications, where individually designed formats
    might be more direct and easily understood,  but RDF's generality offers greater value from
    sharing. The value of information thus increases as it becomes
    accessible to more applications across the entire Internet.</p>

    <h3><a id="section-design-goals" name="section-design-goals">2.2 Design Goals</a></h3>

    <p>The design of RDF is intended to meet the following goals:</p>

    <ul>
      <li>having a simple data model</li>
      <li>having formal semantics and provable inference</li>
      <li>using an extensible URI-based vocabulary</li>
      <li>using an XML-based syntax</li>
      <li>supporting use of XML schema datatypes</li>
      <li>allowing anyone to make statements about any
      resource</li>
   </ul>

    <h4><a id="section-simple-data-model" name="section-simple-data-model">2.2.1 A Simple Data
    Model</a></h4>

    <p>RDF has a simple data model that is easy for applications to
    process and manipulate. The data model is independent of any
    specific serialization syntax.</p>

      <p class="note"><strong>Note:</strong> the term "model" used here in "data model" has a
      completely different sense to its use in the term "model theory".
      See  [<a href=
      "#ref-rdf-semantics">RDF-SEMANTICS</a>]
      for more information about "model
      theory" as used in the literature of mathematics and logic.</p>

    <h4><a id="section-formal-semantics" name="section-formal-semantics">2.2.2 Formal Semantics
    and Inference</a></h4>

    <p>RDF has a formal semantics which provides a dependable basis for
    reasoning about the meaning of an RDF expression. In particular, it
    supports rigorously defined notions of entailment which provide a
    basis for defining reliable rules of inference in RDF data.</p>

    <h4><a id="section-extensible-vocab" name="section-extensible-vocab">2.2.3 Extensible
    URI-based Vocabulary</a></h4>

    <p>The vocabulary is fully extensible, being based on URIs with
    optional fragment identifiers (<cite>URI references</cite>, or
    <cite>URIrefs</cite>). URI references are used for naming all kinds
    of things in RDF.</p>

    <p>The other kind of value that appears in RDF data is a
    literal.</p>

    <h4><a id="section-xml-serialization" name="section-xml-serialization">2.2.4 XML-based
    Syntax</a></h4>

    <p>RDF has a recommended XML serialization form [<a href=
    "#ref-rdf-syntax">RDF-SYNTAX</a>], which can be used to encode the
    data model for exchange of information among applications.</p>

    <h4><a id="section-use-xsd" name="section-use-xsd">2.2.5 Use XML Schema
    Datatypes</a></h4>

    <p>RDF can use values represented according to XML schema datatypes
    [<a href="#ref-xml-schema2">XML-SCHEMA2</a>], thus assisting the
    exchange of information between RDF and other XML applications.</p>

    <h4><a id="section-anyone" name="section-anyone">2.2.6 Anyone Can Make
    Statements About Any Resource</a></h4>

    <p>To facilitate operation at Internet scale, RDF is an
    open-world framework that allows anyone to make statements
    about any resource.</p>
    <p>In general, it is not assumed that complete information
    about any resource is available. RDF does not prevent anyone
    from making assertions that are nonsensical or inconsistent
    with other statements, or the world as people see it. Designers
    of applications that use RDF should be aware of this and may
    design their applications to tolerate incomplete or
    inconsistent sources of information.</p>

<!-- here -->
    <h2><a id="section-Concepts" name="section-Concepts">3. RDF
    Concepts</a></h2>

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

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

      <li>URI-based vocabulary</li>

      <li>Datatypes</li>

      <li>Literals</li>

      <li>XML serialization syntax</li>

      <li>Expression of simple facts</li>

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

    <h3><a id="section-data-model" name="section-data-model">3.1 Graph Data
    Model</a></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="block">
      <p><img src="Graph-ex.gif"
      alt="image of the RDF triple comprising (subject, predicate, object)"
       height="72" width="361" /></p>
    </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">subject</a>,</li>
      <li>an <a href="#dfn-object">object</a>, and</li>
      <li>a <a href="#dfn-predicate">predicate</a> (also called a
      <a href="#dfn-property">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 href="#section-Graph-Node">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 [<a
    href="#ref-rdf-semantics">RDF-SEMANTICS</a>].</p>


    <h3><a id="section-URI-Vocabulary" name=
    "section-URI-Vocabulary">3.2 URI-based Vocabulary and Node
    Identification</a></h3>


    <p>A node may be a URI with optional fragment identifier (<a
    href="#dfn-URI-reference">URI reference</a>, or <dfn><a
    id="dfn-URIref" name="dfn-URIref">URIref</a></dfn>), a literal,
    or blank (having no separate form of identification).
    Properties are <cite>URI references</cite>. (See [<a
    href="#ref-uris">URI</a>], section 4, for a description of URI
    reference forms, noting that relative URIs are not used in an
    RDF graph. See also <a href="#section-Graph-URIref">section
    6.4</a>.)</p>
    <p>A URI reference or literal used as a node identifies what
    that node represents. A URI reference used as a predicate
    identifies a relationship between the things represented by the nodes it connects. A
    predicate URI reference may also be a node in the graph.</p>
    <p>A <a href="#dfn-blank-node">blank node</a> is a node that is
    not a URI reference 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, but has no intrinsic name.</p>
    <p>A convention used by some linear representations of an RDF
    graph to allow several statements to reference the same
    unidentified resource is to use a <dfn><a
    id="dfn-blank-node-id" name="dfn-blank-node-id">blank node
    identifier</a></dfn>, which is a local identifier that can be
    distinguished from all URIs 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>


    <h3><a name="section-Datatypes-intro" id="section-Datatypes-intro">3.3
    Datatypes</a></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.">
      <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>
    </table>

    <p>RDF predefines just one datatype <a href=
    "#dfn-rdf-XMLLiteral" class="code">rdf:XMLLiteral</a>, 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 URI references.
    The predefined XML Schema
    datatypes [<a href="#ref-xml-schema2">XML-SCHEMA2</a>] are expected
    to be widely used for this purpose.</p>


    <p>RDF provides no mechanism for defining new datatypes. XML Schema
    Datatypes [<a href="#ref-xml-schema2">XML-SCHEMA2</a>] provides an
    extensibility framework suitable for defining new datatypes for use
    in RDF.</p>

    <h3><a name="section-Literals" id="section-Literals">3.4
    Literals</a></h3>

    <p>Literals 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 a URI, 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>plain</cite> or <cite>typed</cite> :</p>

    <ul>
      <li>A <a href="#dfn-plain-literal" >plain literal</a> is a string combined
      with an optional language tag. This may be used for
      plain text in a natural language. As recommended in the RDF
      formal semantics [<a href=
      "#ref-rdf-semantics">RDF-SEMANTICS</a>], these plain literals are
      self-denoting.</li>


      <li>A <a href="#dfn-typed-literal" >typed literal</a> is a string combined with a
      datatype URI. It denotes the
      member of the identified datatype's value space obtained by
      applying the lexical-to-value mapping to the literal string.</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.">
      <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>
    </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.
<a href="#ref-xhtml">[XHTML]</a> 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>
The string in both plain and typed literals is recommended to
be in Unicode Normal Form C <a href="#ref-nfc">[NFC]</a>. This is motivated
by <a href="#ref-charmod">[CHARMOD]</a> particularly
<a href="http://www.w3.org/TR/2003/WD-charmod-20030822/#sec-Normalization">section 4
Early Uniform Normalization</a>.
</p>

    <h3><a id="section-SimpleFacts" name="section-SimpleFacts">3.5
    RDF Expression of Simple Facts</a></h3>


    <p>Some simple facts indicate a relationship between
       two things.
Such a fact may be represented as an RDF triple in which the predicate
names the relationship, and the subject and object denote the two things.


     A familiar representation of such a fact might be
    as a row in a table in a relational database. The table has
    two columns, corresponding to the subject and the object of the
    RDF triple.
    The name of the table corresponds to the predicate
    of the RDF triple. A further familiar representation may be as a
    two place predicate
    in first order logic.</p>

    <p>
Relational databases permit a table to have an arbitrary number of columns,
a row of which expresses information corresponding to a predicate in first
order logic with an arbitrary number of places.  Such a row, or predicate,
has to be decomposed for representation as RDF triples.  A simple form of
decomposition introduces a new blank node, corresponding to the row, and a
new triple is introduced for each cell in the row.  The subject of each
triple is the new blank node, the predicate corresponds to the column name,
and object corresponds to the value in the cell.  The new blank node may
also have an <span class="code">rdf:type</span> property whose value corresponds
to the table name.
</p>

   <p>As an example, consider Figure 6 from the
    [<a href=
    "#ref-rdf-primer">RDF-PRIMER</a>]:

</p>

            <div class="figure">
              <img src="fig6may19" alt=
              "Using a Blank Node" width="100%" /><br />
               RDF Primer Figure 6: Using a Blank Node
            </div>


 <p>
This information might correspond to a row in a table <span class="code">"STAFFADDRESSES"</span>,
 with a primary key
<span class="code">STAFFID</span>,
 and additional columns
<span class="code">STREET</span>,
<span class="code">STATE</span>,
<span class="code">CITY</span> and
<span class="code">POSTALCODE</span>.
  </p>

    <p>
Thus, a more complex fact is expressed in RDF using a
conjunction (logical-AND) of simple binary relationships.  RDF does not
provide means to express negation (NOT) or disjunction (OR).  </p>

    <p>Through its use of extensible URI-based vocabularies, RDF
    provides for expression of facts about arbitrary subjects; i.e.
    assertions of named properties about specific named things. A URI
    can be constructed for any thing that can be named, so RDF facts
    can be about any such things. <!--
            And, as noted above, RDF also
            provides for expression of assertions about unnamed things, which
            may be fully identifiable in terms of such assertions [<a
            href="#ref-tap-rbd">TAP-RBD</a>].
            -->
    </p>


    <h3><a id="section-Entailment" name="section-Entailment">3.6
    Entailment</a></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 [<a href=
    "#ref-rdf-semantics">RDF-SEMANTICS</a>].
In brief,  an RDF expression A is said to
<dfn>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>


    <h2><a id="section-URIspaces" name="section-URIspaces">4. RDF
    Vocabulary URI and Namespace (Normative)</a></h2>

    <p>

RDF uses URI references to identify resources and properties.  Certain
URI references are given specific meaning by RDF.  Specifically, URI
references with the following leading substring are defined by the RDF
specifications:

</p>
    <ul>
      <li><span
      class="code">http://www.w3.org/1999/02/22-rdf-syntax-ns#</span>
      (conventionally associated with namespace prefix <span
      class="code">rdf:</span>)</li>
<!--
      <li><span
      class="code">http://www.w3.org/2000/01/rdf-schema#</span>
      (conventionally associated with namespace prefix <span
      class="code">rdfs:</span>)</li>
-->
    </ul>
    <p>Used with the RDF/XML serialization, this URI prefix
    string corresponds to XML namespace names [<a
    href="#ref-namespaces">XML-NS</a>] associated with the RDF
    vocabulary terms.</p>
    <div class="note">
      <p><strong>Note:</strong> this namespace name is the same
      as that used in the earlier RDF recommendation [<a
      href="#ref-rdf-ms">RDF-MS</a>].</p>
    </div>
    <p>Vocabulary terms in the <span class="code">rdf:</span>
    namespace are listed in <a
    href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/#section-Namespace">
    section 5.1</a> of the RDF syntax specification [<a
    href="#ref-rdf-syntax">RDF-SYNTAX</a>]. Some of these terms are
    defined by the RDF specifications to denote specific concepts.
    Others have syntactic purpose (e.g. rdf:ID is part of
    the RDF/XML syntax).</p>
<!--
    <p>Vocabulary terms defined in the <span
    class="code">rdfs:</span> namespace are defined in the RDF
    schema vocabulary specification [<a
    href="#ref-rdf-vocabulary">RDF-VOCABULARY</a>].</p>
-->

   <h2><a name="section-Datatypes" id="section-Datatypes">5.
    Datatypes (Normative)</a></h2>

<p>
The datatype abstraction used in RDF is compatible with
the abstraction used in
XML Schema Part 2:
    Datatypes [<a href="#ref-xml-schema2">XML-SCHEMA2</a>].</p>
<p>
A datatype consists of a lexical space, a value space and a lexical-to-value
mapping.
</p>
<p>The <dfn><a id="dfn-lexical-space"
    name="dfn-lexical-space">lexical space</a></dfn> of a datatype is a set of Unicode [<a
      href="#ref-unicode">UNICODE</a>] strings.</p>
<p>
The <dfn><a id="dfn-lexical-to-value-mapping" name=
    "dfn-lexical-to-value-mapping">lexical-to-value mapping</a></dfn> of a datatype is a set of pairs whose
first element belongs to
the <dfn><a href="#dfn-lexical-space">lexical space</a></dfn> of the datatype,
and the second element belongs to the
 <dfn><a id="dfn-value-space"
    name="dfn-value-space">value space</a></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 URI references.
</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.
[<a href=
      "#ref-rdf-semantics">RDF-SEMANTICS</a>] 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><strong>Note:</strong> 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 [<a href="#ref-xml-schema1">XML-SCHEMA1</a>],
<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>

    <h3><a id="section-XMLLiteral" name="section-XMLLiteral">5.1 XML
    Content within an RDF Graph</a></h3>

    <p>RDF provides for XML content as a possible literal value. This
    typically originates from the use of
    <span class="code">rdf:parseType="Literal"</span> in the RDF/XML Syntax [<a
    href="#ref-rdf-syntax">RDF-SYNTAX</a>].</p>

    <p>Such content is indicated in an RDF graph using a typed literal
    whose datatype is a special built-in datatype
    <dfn><a id="dfn-rdf-XMLLiteral" name= "dfn-rdf-XMLLiteral" class="code">rdf:XMLLiteral</a></dfn>,
    defined as follows.</p>


    <dl>
      <dt><a name="XMLLiteral-uri" id="XMLLiteral-uri">A URI reference for
identifying this datatype</a></dt>

      <dd>is
      <span class="code">http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral</span>.</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>
[<a href="#ref-xml">XML</a>];
</li>
<li>for which encoding as UTF-8
[<a href="#ref-rfc-2279">RFC 2279</a>] 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>) <a href="#ref-xml-xc14n">[XML-XC14N]</a>;
</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> <a href="#ref-namespaces">[XML-NS]</a></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 XML schema datatype
[<a href="#ref-xml-schema2">XML-SCHEMA2</a>];</li>

<li>disjoint from the set of Unicode character strings [<a
      href="#ref-unicode">UNICODE</a>] strings;</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"><strong>Note:</strong> Not all values of this datatype are compliant
      with XML 1.1 [<a href="#ref-xml-1-1">XML 1.1</a>]. 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"><strong>Note:</strong> XML values can be thought of as the
[<a href="#ref-xml-infoset">XML-INFOSET</a>] or the
[<a href="#ref-xpath">XPATH</a>]
nodeset corresponding to the lexical form, with an appropriate equality
function.</p>

      <p class="note"><strong>Note:</strong> 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>


    <h2><a id="section-Graph-syntax" name="section-Graph-syntax">6.
    Abstract Syntax (Normative)</a></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 [<a
    href="#ref-rdf-tests">RDF-TESTS</a>] specification.</p>

<div class="note">
<p><a name="implementation-note" id="implementation-note"><strong>Implementation Note:</strong></a>
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>

    <h3><a id="section-triples" name="section-triples">6.1 RDF
    Triples</a><a id="xtocid103646" name="xtocid103646"> </a></h3>

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

    <ul>
      <li>the <dfn><a id="dfn-subject" name="dfn-subject">subject</a></dfn>,
which is an <a href="#dfn-URI-reference">RDF URI reference</a>
or a <a href="#dfn-blank-node">blank node</a>
</li>

      <li>the <dfn><a id="dfn-predicate" name="dfn-predicate">predicate</a></dfn>, which is an <a href=
      "#dfn-URI-reference">RDF URI reference</a></li>

      <li>the <dfn><a id="dfn-object" name="dfn-object">object</a></dfn>,
which is an <a href="#dfn-URI-reference">RDF URI reference</a>,
a <a href="#dfn-literal">literal</a>
or a <a href="#dfn-blank-node">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><a name="dfn-property"
     id="dfn-property">property</a></dfn> of the triple.</p>

    <h3><a id="section-rdf-graph" name="section-rdf-graph">6.2 RDF Graph</a><a id="xtocid103647" name="xtocid103647"> </a></h3>

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

    <p>The set of <dfn><a name="dfn-node" id="dfn-node">nodes</a><a name="section-Graph-Node" id="section-Graph-Node"> </a></dfn> of an RDF graph is the set of subjects and objects of
    triples in the graph.</p>


    <h3><a id="section-graph-equality" name="section-graph-equality">6.3 Graph
    Equivalence</a></h3>

    <p>Two RDF graphs <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 href=
      "#dfn-literal">RDF literals</a> <var>lit</var> which
      are nodes of <var>G</var>.</li>

      <li><var>M(uri)=uri</var> for all <a href=
      "#dfn-URI-reference">RDF URI references</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>


    <h3><a id="section-Graph-URIref" name="section-Graph-URIref">6.4
    RDF URI References</a></h3>


    <p>A <dfn><a id="dfn-URI-reference" name="dfn-URI-reference">URI reference</a></dfn> within an RDF graph (an RDF URI reference) is a
    Unicode string [<a href="#ref-unicode">UNICODE</a>] that:
</p>
<ul>
<li>does not contain any control characters ( #x00 - #x1F, #x7F-#x9F)
</li>
<li>and
        would produce a
valid URI character sequence (per RFC2396 [<a href=
        "#ref-uris">URI</a>], sections 2.1)
representing an absolute URI with optional
fragment identifier
 when subjected to the encoding described below.
</li>
</ul>
<p>
The encoding consists of:
</p>
<ol>
<li>encoding the Unicode string as UTF-8
[<a href=
      "#ref-rfc-2279">RFC-2279</a>], giving a sequence of octet values.
</li>
<li>
%-escaping octets that do not correspond to permitted US-ASCII characters.
</li>
</ol>
<p>
The disallowed octets that must be %-escaped include all those that do not
correspond to US-ASCII characters, and the excluded characters listed in
Section 2.4 of [<a href=
        "#ref-uris">URI</a>], except for the number sign (#), percent sign (%),
and the square bracket characters re-allowed in [<a href=
        "#ref-rfc-2732">RFC-2732</a>].
</p>
<p>
Disallowed octets must be escaped with the URI escaping mechanism (that is, converted to %HH,
where HH is the 2-digit hexadecimal numeral corresponding to the octet value).
</p>


    <p>Two RDF URI references are equal if and only if they compare as
    equal, character by character, as Unicode strings.</p>

    <div class="note">

      <p><strong>Note:</strong> RDF URI references are compatible with the <a
      href=
      "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#anyURI"><cite>
      anyURI</cite></a> datatype as defined by XML schema datatypes [<a
      href="#ref-xml-schema2">XML-SCHEMA2</a>], constrained to be an
      absolute rather than a relative URI reference.</p>

      <p><strong>Note:</strong> RDF URI references are compatible with <a href=
      "http://www.w3.org/TR/2003/PR-xml-names11-20031105/#IRIs">International Resource
      Identifiers</a> as defined by [<a href="#ref-xml-names11">XML
      Namespaces 1.1</a>].</p>


      <p><strong>Note:</strong> this section anticipates an RFC on Internationalized Resource
Identifiers. Implementations may issue warnings concerning the use
of RDF URI References that do not conform with [<a href="#ref-iri">IRI draft</a>] or its
successors.</p>

      <p><strong>Note:</strong> The restriction to absolute URI references is
      found in this abstract syntax. When there is a well-defined base
      URI, concrete syntaxes, such as RDF/XML, may permit relative URIs
      as a shorthand for such absolute URI references.</p>


      <p><strong>Note:</strong> Because of the risk of confusion between
RDF URI references that would
be equivalent if derefenced, the use of %-escaped characters in RDF URI
references is strongly discouraged. See also the
<a href=
"http://www.w3.org/2001/tag/issues.html#URIEquivalence-15">
URI equivalence issue</a> of
the Technical Architecture Group [<a href="#ref-TAG">TAG</a>].</p>
    </div>

    <h3><a id="section-Graph-Literal" name="section-Graph-Literal">6.5
    RDF Literals</a></h3>


<p>A <dfn><a id="dfn-literal" name="dfn-literal">literal</a></dfn> in an RDF graph
contains one or two named components.</p>
<p>All literals have a <dfn><a id="dfn-lexical-form" name=
      "dfn-lexical-form">lexical form</a></dfn> being a Unicode [<a
      href="#ref-unicode">UNICODE</a>] string, which SHOULD be in Normal Form C [<a
      href="#ref-nfc">NFC</a>].</p>


<p><dfn><a id="dfn-plain-literal" name="dfn-plain-literal">Plain literals</a></dfn> have
 a <a href="#dfn-lexical-form">lexical form</a> and optionally a
<dfn><a id="dfn-language-identifier" name=
      "dfn-language-identifier">language tag</a></dfn> as
defined by [<a href="#ref-rfc-3066">RFC-3066</a>], normalized to lowercase.</p>

<p><dfn><a id="dfn-typed-literal" name="dfn-typed-literal">Typed literals</a></dfn> have a <a href="#dfn-lexical-form">lexical form</a> and a <dfn><a id="dfn-datatype-URI" name=
      "dfn-datatype-URI">datatype URI</a></dfn> being an <a href=
      "#dfn-URI-reference">RDF URI reference</a>.</p>


    <div class="note">
      <p><strong>Note:</strong> Literals in which the lexical form begins with a
      composing character (as defined by [<a href=
      "#ref-charmod">CHARMOD</a>]) are allowed however they may cause
      interoperability problems, particularly with XML version 1.1 [<a
      href="#ref-xml-1-1">XML 1.1</a>].</p>

      <p><strong>Note:</strong> 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><strong>Note:</strong> 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>

    <h4><a id="section-Literal-Equality" name=
    "section-Literal-Equality">6.5.1 Literal Equality</a></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 URIs.</li>

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

      <p class="note"><strong>Note:</strong> RDF Literals are distinct and distinguishable
      from RDF URI references; e.g. http://example.org as an RDF
      Literal (untyped, without a language tag) is not equal to
      http://example.org as an RDF URI reference.</p>

    <h4><a id="section-Literal-Value" name=
    "section-Literal-Value">6.5.2 The Value Corresponding to a Typed
    Literal</a></h4>

    <p>The datatype URI 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, URIs such as
    <span class="code">http://www.w3.org/2001/XMLSchema#int</span> are used. The URI
    of the datatype <a href=
    "#section-XMLLiteral" class="code">rdf:XMLLiteral</a> may be used.
    There may be other, implementation dependent, mechanisms by which
    URIs 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 URI to
    the lexical form.
    </p>

    <p>
 If the lexical form is not in
    the lexical space of the datatype associated with the datatype URI,
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"><strong>Note:</strong>
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
[<a href=
    "#ref-rdf-semantics">RDF-SEMANTICS</a>]) are usually
more helpful than syntactic equality (see
<a href="#section-graph-equality">
section
6.3</a>).</p>
<h3><a id="section-blank-nodes" name="section-blank-nodes">6.6 Blank Nodes</a></h3>
<p>
The <dfn><a id="dfn-blank-node" name="dfn-blank-node">blank nodes</a></dfn> in an RDF graph
are drawn from an infinite set.
This set of blank nodes, the set of all <a href="#dfn-URI-reference">RDF URI references</a>
and the set of all <a href="#dfn-literal">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>


    <h2><a id="section-fragID" name="section-fragID">7. Fragment
    Identifiers</a></h2>

    <p>RDF uses an <a href="#dfn-URI-reference">RDF URI
    Reference</a>, which may include a fragment identifier, as a
    context free identifier for a resource. RFC 2396 [<a
    href="#ref-uris">URI</a>] 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 a URI reference in an RDF graph is treated
    with respect to the MIME type <span
    class="code">application/rdf+xml</span> [<a
    href="#ref-rdf-mime-type">RDF-MIME-TYPE</a>]. Given an RDF URI
    reference consisting of an absolute URI and a fragment
    identifier, the fragment identifer identifies the same thing
    that it does in an <span
    class="code">application/rdf+xml</span> representation of the
    resource identified by the absolute URI component. Thus:</p>
    <ul>
      <li>we assume that the URI part (i.e. excluding fragment
      identifier) identifies a resource, which is presumed to have
      an RDF representation. So when <span
      class="code">eg:someurl#frag</span> is used in an RDF
      document, <span class="code">eg:someurl</span> is taken to
      designate some RDF document (even when no such document can
      be retrieved).</li>
      <li><span class="code">eg:someurl#frag</span> means the thing
      that is indicated, according to the rules of the <span
      class="code">application/rdf+xml</span> MIME content-type as
      a "fragment" or "view" of the RDF document at <span
      class="code">eg:someurl</span>. If the document does not
      exist, or cannot be retrieved, or is available only in
      formats other than <span
      class="code">application/rdf+xml</span>, 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 <span
      class="code">application/rdf+xml</span> document acts as an
      intermediary between some Web retrievable documents (itself,
      at least, also any other Web retrievable URIs that it may
      use, possibly including schema URIs 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 URI references 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 URIs
    in an RDF graph.</p>


    <h2 class="nonum"><a id="section-Acknowledgments" name=
    "section-Acknowledgments">8. Acknowledgments</a></h2>

    <p>This document contains a significant contribution from Pat
    Hayes, Sergey Melnik and Patrick Stickler, under whose leadership
    was developed the framework described in the RDF family of
    specifications for representing datatyped values, such as integers
    and dates.</p>

    <p>The editors acknowledge valuable contributions from the
    following: <!--</p>

    <ul>-->
      <!--<li>-->Frank Manola, <!--</li>-->

      <!--<li>-->Pat Hayes, <!--</li>-->

      <!--<li>-->Dan Brickley, <!--</li>-->

      <!--<li>-->Jos de Roo, <!--</li>-->

      <!--<li>-->Dave Beckett, <!--</li>-->

      <!--<li>-->Patrick Stickler, <!--</li>-->

      <!--<li>-->Peter F. Patel-Schneider, <!--</li>-->

      <!--<li>-->Jerome Euzenat, <!--</li>-->

      <!--<li>-->Massimo Marchiori, <!--</li>-->

      <!--<li>-->Tim Berners-Lee, <!--</li>-->

      <!--<li>-->Dave Reynolds <!--</li>-->

      <!--<li>-->and Dan Connolly. <!--</li>-->
<!--
      <li class="todo">[[[Other contributors]]]</li>
    </ul>
-->
</p>
    <p>Jeremy Carroll thanks <a href="mailto:oreste@w3.org">Oreste
    Signore</a>, his host at the <a href="http://www.w3c.it/">W3C
    Office in Italy</a> and <a href="http://www.isti.cnr.it" lang="it"
    xml:lang="it">Istituto di Scienza e Tecnologie dell'Informazione
    "Alessandro Faedo"</a>, part of the <a href="http://www.cnr.it"
    lang="it" xml:lang="it">Consiglio Nazionale delle Ricerche</a>,
    where Jeremy is a visiting researcher.</p>

    <p>This document is a product of extended deliberations by the
    RDFcore Working Group, whose members have included:

<!--</p><ul>-->
      <!--<li>-->Art Barstow (W3C), <!--</li>-->

      <!--<li>-->Dave Beckett (ILRT), <!--</li>-->

      <!--<li>-->Dan Brickley (ILRT), <!--</li>-->

      <!--<li>-->Dan Connolly (W3C), <!--</li>-->

      <!--<li>-->Jeremy Carroll (Hewlett Packard), <!--</li>-->

      <!--<li>-->Ron Daniel (Interwoven Inc), <!--</li>-->

      <!--<li>-->Bill dehOra (InterX), <!--</li>-->

      <!--<li>-->Jos De Roo (AGFA), <!--</li>-->

      <!--<li>-->Jan Grant (ILRT), <!--</li>-->

      <!--<li>-->Graham Klyne (Nine by Nine), <!--</li>-->

      <!--<li>-->Frank Manola (MITRE Corporation), <!--</li>-->

      <!--<li>-->Brian McBride (Hewlett Packard), <!--</li>-->

      <!--<li>-->Eric Miller (W3C), <!--</li>-->

      <!--<li>-->Stephen Petschulat (IBM), <!--</li>-->

      <!--<li>-->Patrick Stickler (Nokia), <!--</li>-->

      <!--<li>-->Aaron Swartz (HWG), <!--</li>-->

      <!--<li>-->Mike Dean (BBN Technologies / Verizon), <!--</li>-->

      <!--<li>-->R. V. Guha (Alpiri Inc), <!--</li>-->

      <!--<li>-->Pat Hayes (IHMC), <!--</li>-->

      <!--<li>-->Sergey Melnik (Stanford University) and <!--</li>-->

      <!--<li>-->Martyn Horner (Profium Ltd). <!--</li>-->
    </p> <!--</ul>-->
    <p>This specification also 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. RDF and RDF Schema
    Working Group members who contributed to this earlier work are:

     <!--</p><ul>-->
      <!--<li>-->Nick Arnett (Verity), <!--</li>-->

      <!--<li>-->Tim Berners-Lee (W3C), <!--</li>-->

      <!--<li>-->Tim Bray (Textuality), <!--</li>-->

      <!--<li>-->Dan Brickley (ILRT / University of Bristol), <!--</li>-->

      <!--<li>-->Walter Chang (Adobe), <!--</li>-->

      <!--<li>-->Sailesh Chutani (Oracle), <!--</li>-->

      <!--<li>-->Dan Connolly (W3C), <!--</li>-->

      <!--<li>-->Ron Daniel (DATAFUSION), <!--</li>-->

      <!--<li>-->Charles Frankston (Microsoft), <!--</li>-->

      <!--<li>-->Patrick Gannon (CommerceNet), <!--</li>-->

      <!--<li>-->R. V. Guha (Epinions, previously of Netscape
      Communications), <!--</li>-->

      <!--<li>-->Tom Hill (Apple Computer), <!--</li>-->

      <!--<li>-->Arthur van Hoff (Marimba), <!--</li>-->

      <!--<li>-->Renato Iannella (DSTC), <!--</li>-->

      <!--<li>-->Sandeep Jain (Oracle), <!--</li>-->

      <!--<li>-->Kevin Jones, (InterMind), <!--</li>-->

      <!--<li>-->Emiko Kezuka (Digital Vision Laboratories), <!--</li>-->

      <!--<li>-->Joe Lapp (webMethods Inc.), <!--</li>-->

      <!--<li>-->Ora Lassila (Nokia Research Center), <!--</li>-->

      <!--<li>-->Andrew Layman (Microsoft), <!--</li>-->

      <!--<li>-->Ralph LeVan (OCLC), <!--</li>-->

      <!--<li>-->John McCarthy (Lawrence Berkeley National Laboratory), <!--</li>-->

      <!--<li>-->Chris McConnell (Microsoft), <!--</li>-->

      <!--<li>-->Murray Maloney (Grif), <!--</li>-->

      <!--<li>-->Michael Mealling (Network Solutions), <!--</li>-->

      <!--<li>-->Norbert Mikula (DataChannel), <!--</li>-->

      <!--<li>-->Eric Miller (OCLC), <!--</li>-->

      <!--<li>-->Jim Miller (W3C, emeritus), <!--</li>-->

      <!--<li>-->Frank Olken (Lawrence Berkeley National Laboratory), <!--</li>-->

      <!--<li>-->Jean Paoli (Microsoft), <!--</li>-->

      <!--<li>-->Sri Raghavan (Digital/Compaq), <!--</li>-->

      <!--<li>-->Lisa Rein (webMethods Inc.), <!--</li>-->

      <!--<li>-->Paul Resnick (University of Michigan), <!--</li>-->

      <!--<li>-->Bill Roberts (KnowledgeCite), <!--</li>-->
i
      <!--<li>-->Tsuyoshi Sakata (Digital Vision Laboratories), <!--</li>-->

      <!--<li>-->Bob Schloss (IBM), <!--</li>-->

      <!--<li>-->Leon Shklar (Pencom Web Works), <!--</li>-->

      <!--<li>-->David Singer (IBM), <!--</li>-->

      <!--<li>-->Wei (William) Song (SISU), <!--</li>-->

      <!--<li>-->Neel Sundaresan (IBM), <!--</li>-->

      <!--<li>-->Ralph Swick (W3C), <!--</li>-->

      <!--<li>-->Naohiko Uramoto (IBM), <!--</li>-->

      <!--<li>-->Charles Wicksteed (Reuters Ltd.), <!--</li>-->

      <!--<li>-->Misha Wolf (Reuters Ltd.) and <!--</li>-->

      <!--<li>-->Lauren Wood (SoftQuad). <!--</li>-->
    <!--</ul>--></p>

    <h2 class="nonum"><a id="section-References" name=
    "section-References">9. References</a></h2>

    <h3><a id="section-Normative-References" name=
    "section-Normative-References"></a>9.1 Normative References</h3>

    <dl>


          <dt><a id="ref-rdf-semantics"
          name="ref-rdf-semantics"></a>[RDF-SEMANTICS]</dt>
	  <dd><cite><a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/">RDF Semantics</a></cite>, Patrick Hayes, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ . <a href="http://www.w3.org/TR/rdf-mt/">Latest version</a> available at http://www.w3.org/TR/rdf-mt/ .</dd>


          <dt><a id="ref-rdf-syntax"
          name="ref-rdf-syntax"></a>[RDF-SYNTAX]</dt>

	  <dd><cite><a href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/">RDF/XML Syntax Specification (Revised)</a></cite>, Dave Beckett, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/ . <a href="http://www.w3.org/TR/rdf-syntax-grammar/">Latest version</a> available at http://www.w3.org/TR/rdf-syntax-grammar/ .</dd>


      <dt><a id="ref-rdf-mime-type" name=
      "ref-rdf-mime-type"></a>[RDF-MIME-TYPE]</dt>
 <dd>
    <cite><a href="http://www.iana.org/assignments/media-types/">MIME Media Types</a></cite>, 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><a id="ref-xml" name="ref-xml"></a>[XML]</dt>

      <dd><cite><a href=
      "http://www.w3.org/TR/2000/REC-xml-20001006">Extensible Markup
      Language (XML) 1.0, Second Edition</a></cite>, T. Bray, J. Paoli,
      C.M. Sperberg-McQueen and E. Maler, Editors. World Wide Web
      Consortium. 6 October 2000. This version is
      <span>http://www.w3.org/TR/2000/REC-xml-20001006</span>. The
      latest version of XML is available at <a href=
      "http://www.w3.org/TR/REC-xml">http://www.w3.org/TR/REC-xml</a>.</dd>

      <dt><a id="ref-namespaces" name=
      "ref-namespaces"></a>[XML-NS]</dt>

      <dd><cite><a href=
      "http://www.w3.org/TR/1999/REC-xml-names-19990114/">Namespaces in
      XML</a></cite>, T. Bray, D. Hollander and A. Layman, Editors.
      World Wide Web Consortium. 14 January 1999. This version is
      <span>http://www.w3.org/TR/1999/REC-xml-names-19990114/</span>.
      The <a href="http://www.w3.org/TR/REC-xml-names/">latest version
      of Namespaces in XML</a> is available at
      http://www.w3.org/TR/REC-xml-names/.</dd>

      <dt><a id="ref-rfc-2279" name="ref-rfc-2279"></a>[RFC-2279]</dt>

      <dd><i><a href="http://www.isi.edu/in-notes/rfc2279.txt">RFC 2279
      - UTF-8, a transformation format of ISO 10646</a></i>, F.
      Yergeau, IETF, January 1998. This document is
      http://www.isi.edu/in-notes/rfc2279.txt.</dd>


      <dt><a id="ref-uris" name="ref-uris"></a>[URI]</dt>

      <dd><cite><a href="http://www.isi.edu/in-notes/rfc2396.txt">RFC
      2396 - Uniform Resource Identifiers (URI): Generic
      Syntax</a></cite>, T. Berners-Lee, R. Fielding and L. Masinter,
      IETF, August 1998. This document is
      http://www.isi.edu/in-notes/rfc2396.txt.</dd>

      <dt><a id="ref-rfc-2732" name="ref-rfc-2732"></a>[RFC-2732]</dt>

      <dd><i><a href="http://www.isi.edu/in-notes/rfc2732.txt">RFC 2732
      - Format for Literal IPv6 Addresses in URL's</a></i>, R. Hinden,
      B. Carpenter and L. Masinter, IETF, December 1999. This document
      is http://www.isi.edu/in-notes/rfc2732.txt.</dd>


      <dt><a id="ref-unicode" name="ref-unicode"></a>[UNICODE]</dt>

      <dd><cite>The Unicode Standard, Version 3</cite>, The Unicode
      Consortium, Addison-Wesley, 2000. ISBN 0-201-61633-5, as updated
      from time to time by the publication of new versions. (See <a
      href=
      "http://www.unicode.org/unicode/standard/versions/">http://www.unicode.org/unicode/standard/versions/</a>
      for the latest version and additional information on versions of
      the standard and of the Unicode Character Database).</dd>

      <dt><a id="ref-nfc" name="ref-nfc"></a>[NFC]</dt>

      <dd><a href=
      "http://www.unicode.org/unicode/reports/tr15/"><cite>Unicode
      Normalization Forms,</cite></a> Unicode Standard Annex #15, Mark
      Davis, Martin D&uuml;rst. (See <a href=
      "http://www.unicode.org/unicode/reports/tr15/">http://www.unicode.org/unicode/reports/tr15/</a>
      for the latest version).</dd>


      <dt><a id="ref-rfc-3066" name="ref-rfc-3066"></a>[RFC-3066]</dt>

      <dd><i><a href="http://www.isi.edu/in-notes/rfc3066.txt">RFC 3066
      - Tags for the Identification of Languages</a></i>, H.
      Alvestrand, IETF, January 2001. This document is
      http://www.isi.edu/in-notes/rfc3066.txt.</dd>

<dt>
    <a id="ref-xml-xc14n" name="ref-xml-xc14n">[XML-XC14N]</a>
  </dt>
  <dd><cite><a href="http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/">Exclusive XML Canonicalization Version 1.0</a></cite>, J. Boyer, D.E. Eastlake 3rd, J. Reagle, Authors/Editors. W3C Recommendation.  World Wide Web Consortium, 18 July 2002.  This version of Exclusive XML
Canonicalization is <span>http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/</span>.
The <a href="http://www.w3.org/TR/xml-exc-c14n/">latest version of Canonical XML</a> is at http://www.w3.org/TR/xml-exc-c14n.
  </dd>

      <dt><a id="ref-xml-schema2" name=
      "ref-xml-schema2"></a>[XML-SCHEMA2]</dt>

      <dd><cite><a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/">XML Schema
      Part 2: Datatypes</a></cite>, W3C Recommendation, World Wide Web
      Consortium, 2 May 2001.This version is
      http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/. The <a href=
      "http://www.w3.org/TR/xmlschema-2/">latest version</a> is available at
      http://www.w3.org/TR/xmlschema-2/.</dd>


    </dl>

    <h3><a id="section-Informative-References" name=
    "section-Informative-References"></a>9.2 Informational
    References</h3>
		<dl>

          <dt><a id="ref-rdf-tests"
          name="ref-rdf-tests"></a>[RDF-TESTS]</dt>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/">RDF Test Cases</a></cite>, Jan Grant and Dave Beckett, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/ . <a href="http://www.w3.org/TR/rdf-testcases/">Latest version</a> available at http://www.w3.org/TR/rdf-testcases/ .</dd>


          <dt><a id="ref-rdf-vocabulary"
          name="ref-rdf-vocabulary"></a>[RDF-VOCABULARY]</dt>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210/">RDF Vocabulary Description Language 1.0: RDF Schema</a></cite>, Dan Brickley and R. V. Guha, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-schema-20040210/ . <a href="http://www.w3.org/TR/rdf-schema/">Latest version</a> available at http://www.w3.org/TR/rdf-schema/ .</dd>


  <dt><a id="ref-rdf-primer" name="ref-rdf-primer">[RDF-PRIMER]</a>
  </dt>

<dd><cite><a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">RDF Primer</a></cite>, Frank Manola and Eric Miller, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ . <a href="http://www.w3.org/TR/rdf-primer/">Latest version</a> available at http://www.w3.org/TR/rdf-primer/ .</dd>


      <dt><a id="ref-charmod" name="ref-charmod"></a>[CHARMOD]</dt>

      <dd><cite><a href=
      "http://www.w3.org/TR/2003/WD-charmod-20030822/">Character Model
      for the World Wide Web 1.0</a></cite>, M. D&uuml;rst, F. Yergeau,
      R. Ishida, M. Wolf, T. Texin, Editors, World Wide Web
      Consortium Working Draft, work in progress, 22 August 2003.
      This version of the Character Model is
      http://www.w3.org/TR/2003/WD-charmod-20030822/. The <a href=
      "http://www.w3.org/TR/charmod/">latest version of the Character
      Model</a> is at http://www.w3.org/TR/charmod/.</dd>

      <dt><a id="ref-xml-1-1" name="ref-xml-1-1"></a>[XML-1.1]</dt>

      <dd><cite><a href="http://www.w3.org/TR/2002/CR-xml11-20021015/">Extensible Markup
      Language (XML) 1.1</a></cite>, John Cowan, Editor.
W3C Candidate Recommendation 15 October 2002.
This version is
      http://www.w3.org/TR/2002/CR-xml11-20021015/. The <a href=
      "http://www.w3.org/TR/xml11/">latest version</a> is available at
      http://www.w3.org/TR/xml11/.</dd>


      <dt><a id="ref-xml-schema1" name=
      "ref-xml-schema1"></a>[XML-SCHEMA1]</dt>

      <dd><cite><a href="http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/">XML Schema Part 1: Structures</a></cite>
     W3C Recommendation, World Wide Web
      Consortium, 2 May 2001.
This version is
      http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/. The <a href=
      "http://www.w3.org/TR/xmlschema-1/">latest version</a> is available at
      http://www.w3.org/TR/xmlschema-1/.</dd>

      <dt><a id="ref-xml-names11" name=
      "ref-xml-names11"></a>[XML-NAMESPACES-1.1]</dt>

      <dd><cite><a href="http://www.w3.org/TR/2003/PR-xml-names11-20031105/">Namespaces
      in XML 1.1</a></cite>, Tim Bray, Dave Hollander, Andrew Layman,
      Richard Tobin, Editors. W3C Proposed Recommendation 05 November 2003.
This version is
      http://www.w3.org/TR/2003/PR-xml-names11-20031105/. The <a href=
      "http://www.w3.org/TR/xml-names11/">latest version</a> is available at
      http://www.w3.org/TR/xml-names11/.</dd>

      <dt><a id="ref-xml-infoset" name=
      "ref-xml-infoset"></a>[XML-INFOSET]</dt>

      <dd><i><a href="http://www.w3.org/TR/2001/REC-xml-infoset-20011024/">XML
      Information Set</a></i>, John Cowan and Richard Tobin, W3C
      Recommendation, 24 October 2001. This document is
http://www.w3.org/TR/2001/REC-xml-infoset-20011024/.
The <a href=
      "http://www.w3.org/TR/xml-infoset/">latest version</a> is available at
      http://www.w3.org/TR/xml-infoset/.</dd>

  <dt>
    <a id="ref-xpath" name="ref-xpath">[XPATH]</a>
  </dt>
  <dd><cite><a href="http://www.w3.org/TR/1999/REC-xpath-19991116">XML Path Language (XPath) Version 1.0</a></cite>, J. Clark and S. DeRose, Editors.   World Wide Web Consortium, 16 November 1999.  This version of XPath is <span>http://www.w3.org/TR/1999/REC-xpath-19991116</span>.  The <a href="http://www.w3.org/TR/xpath">latest version of XPath</a> is at <span>http://www.w3.org/TR/xpath</span>.
</dd>

      <dt><a id="ref-owl" name="ref-owl"></a>[OWL]</dt>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/">OWL Web Ontology Language Reference</a></cite>, Mike Dean and Guus Schreiber, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-owl-ref-20040210/ . <a href="http://www.w3.org/TR/owl-ref/">Latest version</a> available at http://www.w3.org/TR/owl-ref/ .</dd>

      <dt><a id="ref-rdf-ms" name="ref-rdf-ms"></a>[RDF-MS]</dt>

      <dd><cite><a href=
      "http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/">Resource
      Description Framework (RDF) Model and Syntax
      Specification</a></cite>, O. Lassila and R. Swick, Editors. World
      Wide Web Consortium. 22 February 1999. This version is
      http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/. The <a href=
      "http://www.w3.org/TR/REC-rdf-syntax/">latest version of RDF
      M&amp;S</a> is available at
      http://www.w3.org/TR/REC-rdf-syntax/.</dd>
      <dt><a id="ref-xhtml" name="ref-xhtml"></a>[XHTML]</dt>

      <dd><cite><a href=
      "http://www.w3.org/TR/2002/REC-xhtml1-20020801/">XHTML
1.0 The Extensible HyperText Markup Language (Second Edition)</a></cite>,

 World
      Wide Web Consortium. 26 January 2000, revised 1 August 2002. This version is
      http://www.w3.org/TR/2002/REC-xhtml1-20020801/. The <a href=
      "http://www.w3.org/TR/xhtml1/">latest version of XHTML 1</a> is available at
      http://www.w3.org/TR/xhtml1/.</dd>


      <dt><a id="ref-iri" name="ref-iri"></a>[IRI draft]</dt>

      <dd><i><a href="http://www.w3.org/International/iri-edit/draft-duerst-iri-04"
>Internationalized Resource Identifiers (IRIs)</a></i>,  M. D&uuml;rst
      and M. Suignard, Internet-Draft, June 2003, expires December 2003. This document
      is <span>http://www.w3.org/International/iri-edit/draft-duerst-iri-04</span>.</dd>
      <dt><a id="ref-TAG" name="ref-TAG"></a>[TAG]</dt>

      <dd><i><a href="http://www.w3.org/2001/tag/issues"
>TAG Issues List</a></i>,  W3C Technical Architecture Group.
  This document
      is <span>http://www.w3.org/2001/tag/issues</span>.</dd>
</dl>
    <h1><a id="changes" name="changes"></a>
<a id="section-Revisions" name="section-Revisions">Appendix
    A:</a> Revisions Since Last Call Working Draft of
<a href="http://www.w3.org/TR/2003/WD-rdf-concepts-20031010/">10 October 2003</a> </h1>
<p>
There were no substantive changes.
</p>
<p>
The following editorial changes have been made:
</p>
<dl>
<dt>Wording of Graph Equivalence</dt>
<dd>Following a
<a href="http://lists.w3.org/Archives/Public/www-rdf-comments/2003OctDec/0118">suggestion</a> from
ter Horst,
the wording of
<a href="#section-graph-equality">Section 6.3</a> has been improved.
</dd>
<dt>Avoid 'globally'</dt>
<dd>In response to a
<a href="http://lists.w3.org/Archives/Public/www-rdf-comments/2003OctDec/0118">comment</a> from
ter Horst,
the wording of
<a href="#section-URI-Vocabulary">Section 3.2</a> has been changed,
replacing a single phrase to avoid the word 'globally',
which was undefined and unclear.
</dd>
<dt>%s in RDF URI References</dt>
<dd>
Following a
<a href="http://lists.w3.org/Archives/Public/www-rdf-comments/2003OctDec/0123">comment</a> from
Patel-Schneider, an additional
note has been added, concerning %-escapes in
<a href="#section-Graph-URIref">section 6.4 RDF URI References</a>.
A new informative reference to the
<a href="#ref-TAG">[TAG]</a> issue list has been added.
</dd>
<dt>References</dt>
<dd>Dated references RDF and OWL documents have been updated.</dd>
</dl>

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