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

      <h2 id="doctype">W3C Working Draft 23 January 2003</h2>

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

        <dd><a href=
        "http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/">http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/</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/2002/WD-rdf-concepts-20021108/">http://www.w3.org/TR/2002/WD-rdf-concepts-20021108/</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 class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">  Copyright</a> &#xa9; 2003 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>&#xae;</sup>  (<a href="http://www.lcs.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>This document 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, meaning of
    RDF documents, key concepts, datatyping, character normalization
    and handling of URI references.</p>

    <h2 class="nonum"><a id="status" name="status">Status of this
    Document</a></h2>

<p>This is a W3C
<a href="http://www.w3.org/Consortium/Process-20010719/tr.html#last-call">Last Call Working Draft</a>
of the <a href="http://www.w3.org/2001/sw/RDFCore/">RDF Core Working Group</a>
and has been produced as part of the W3C
<a href="http://www.w3.org/2001/sw/">Semantic Web Activity</a>
(<a href="http://www.w3.org/2001/sw/Activity">Activity Statement</a>).</p>

<p>This document is in the Last Call review period, which ends on
21 February 2003. This document has been endorsed by the RDF
Core Working Group.</p>

<p>This document is being released for review by W3C Members and
other interested parties to encourage feedback and comments,
especially with regard to how the changes made affect existing
implementations and content.</p>


<p>In conformance with
<a href="http://www.w3.org/Consortium/Process-20010719/#ipr">W3C policy</a>
requirements, known patent and
<acronym title="Intellectual Property Rights">IPR</acronym>
constraints associated with this Working Draft are detailed on the
<a href="http://www.w3.org/2001/sw/RDFCore/ipr-statements" rel="disclosure">RDF Core Working Group Patent Disclosure</a> page.</p>

<p>Comments on this document are invited and should be sent to the
public mailing list
<a href="mailto:www-rdf-comments@w3.org">www-rdf-comments@w3.org</a>.
An archive of comments is available at
<a href="http://lists.w3.org/Archives/Public/www-rdf-comments/">http://lists.w3.org/Archives/Public/www-rdf-comments/</a>.
</p>

<p>This is a public W3C Last Call Working Draft for review by W3C
Members and other interested parties. This section describes the
status of this document at the time of its publication. It is a draft
document and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use W3C Working Drafts
as reference material or to cite as other than "work in progress".  A
list of current W3C Recommendations and other technical documents can
be found at <a href="/TR/">http://www.w3.org/TR/</a>.
</p>

    <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 Simple Assertions About Anything</a></li>

                <li class="tocline"><a href="#section-expression-simple">2.2.7
                Arbitrary Expression of Simple Facts</a></li>

                <li class="tocline"><a href="#section-agreements">2.2.8 A
                Basis for Binding Agreements</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">3.3
                Datatypes (Normative)</a></li>

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


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

                <li class="tocline"><a href="#section-Entailment">3.6
                Entailment</a></li>
            <li class="tocline"><a href="#section-URIspaces">3.7 RDF
            Core URI Vocabulary and Namespaces</a></li>
              </ul>
            </li>

            <li class="tocline">
              <a href="#section-Meaning"><strong>4. Meaning of RDF (Normative)</strong></a>

              <ul class="toc">
                <li class="tocline"><a href=
                "#section-AssertedForm">4.1 Asserted and Non-asserted
                Forms</a></li>

                <li class="tocline"><a href="#section-Social">2.4.2
                Social Meaning</a></li>


                <li class="tocline"><a href=
                "#section-authority">4.3 Authoritative Definition
                of Terms</a></li>

                <li class="tocline">
                  <a href="#section-Interaction">4.4 Interaction
                  Between Social and Formal Meaning</a>

                </li>

                    <li class="tocline"><a href=
                    "#section-InteractionExample">4.5
                    Example (Informative)</a></li>
              </ul>
            </li>


        <li class="tocline"><a href="#section-XMLLiteral"><strong>5.
        XML Content within an RDF Graph (Normative)</strong></a></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
            Equality</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>
      </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. It also includes discussion of design goals, meaning of
    RDF documents, key concepts, datatyping, character normalization
    and handling of URI references.</p>

    <p>Normative documentation of the RDF core 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.</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 on
    top of a core.  The RDF core 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 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>.
The meaning of RDF is discussed in <a href="#section-Meaning">section 4</a>,
including discussion of social mechanisms, the interaction between social
 and formal meaning and the implications of
publication of an RDF document.</p>


    <p>RDF's abstract syntax is a graph, which can be serialized using
    XML (but which is quite distinct from XML's tree-based infoset [<a
    href="#ref-xml-infoset">XML-INFOSET</a>]). The abstract syntax
    captures the fundamental structure of RDF, independently of any
    concrete syntax used for serialization. The formal semantics of RDF
    are defined in terms of the abstract syntax. XML content of
    literals is described in <a href="#section-XMLLiteral">section
    5</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 <i>lingua franca</i> 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>A simple data model</li>

      <li>Formal semantics and provable inference</li>

      <li>Extensible URI-based vocabulary</li>

      <li>XML-based syntax</li>

      <li>Support use of XML schema datatypes</li>

      <li>Anyone can make simple assertions about anything</li>

      <li>Universal expression of simple facts</li>

      <li>A basis for legally binding agreements</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 the RDF model theory specification [<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
    Simple Assertions About Anything</a></h4>

    <p>To facilitate operation at Internet scale, RDF is an open-world
    framework that allows anyone to make simple assertions about
    anything. In general, it is not assumed that all information about
    any topic is available. A consequence of this is that RDF cannot
    prevent anyone from making assertions that are nonsensical or
    inconsistent with the world as people see it, and applications that
    build upon RDF need to find ways to deal with incomplete and
    conflicting sources of information. (This is where RDF departs from
    more prescriptive approaches to representing data in XML, which aim
    to present information that is well-formed and complete for an
    application's needs.)</p>

    <h4><a id="section-expression-simple" name="section-expression-simple">2.2.7 Arbitrary
    Expression of Simple Facts</a></h4>

    <p>RDF can represent arbitrary information that can be expressed as
    simple facts. (What constitutes a simple fact is discussed later,
    in <a href="#section-SimpleFacts">section 3.5</a>)</p>

    <h4><a id="section-agreements" name="section-agreements">2.2.8 A Basis for
    Binding Agreements</a></h4>

    <p>RDF is intended to convey assertions that are meaningful to the
    extent that they may, in appropriate contexts, be used to express
    the terms of binding agreements.</p>

    <p>This goal is explored further in <a href=
    "#section-Social">section 4.2</a> below.</p>

    <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>Information as representation 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 can be viewed
    as a directed labelled graph, which consists of nodes and labelled
    directed arcs that link pairs of nodes (these notions are defined
    more formally in <a href="#section-Graph-syntax">section 6</a>).
    The RDF graph is a set of triples:</p>

    <div class="block">
      <p><img src="http://www.w3.org/TR/rdf-concepts/Graph-ex.gif" alt=
      "image of the RDF triple comprising (subject, predicate, object)"
      height="72" width="361" /></p>
    </div>
		<p>Each property arc represents a statement of a relationship between the things denoted by the nodes that it links, having three parts:</p>
		<ol>
      <li>a <a href="#dfn-property"
      >property</a> that describes some
      relationship (also called a <a href="#dfn-predicate"
      >predicate</a>),</li>

      <li>a value that is the <a href="#dfn-subject"
      >subject</a> of the statement, and</li>

      <li>a value that is the <a href="#dfn-object"
      >object</a> of the statement.</li>
    </ol>
		<p>The direction of the arc is significant: it always points toward
    the object of a statement.</p>

    <p>The meaning of an RDF graph is the conjunction (i.e. logical
    AND) of all the statements that it contains.</p>

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

    <p><a href="#section-Graph-Node" >Nodes</a> in an RDF graph are URIs with
    optional fragment identifiers (<a href="#dfn-URI-reference"
    >URI references</a>, or <dfn><a id=
    "dfn-URIref" name="dfn-URIref">URIrefs</a></dfn>), literals, or
    blank (having no separate form of identification). Arcs are
    labelled with <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>The URI reference or literal used as a node identifies what that node
    represents. The label on an arc identifies the relationship between
    the nodes connected by the arc. The arc label may also be a node in
    the graph.</p>

    <p>A <a href="#dfn-blank-node" >blank
    node</a> is an RDF graph 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, and has
    no globally distinguishing identity.</p>

    <p>A convention used by some linear representations of an RDF graph
    to allow several statements to reference the same blank node 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.</p>

    <p>Note that blank node identifiers are <em>not</em> part of the
    RDF abstract syntax, and the representation of statements that use
    blank nodes is entirely dependent on the particular concrete syntax
    used.</p>

    <h3><a name="section-Datatypes" id="section-Datatypes">3.3
    Datatypes (Normative)</a></h3>

    <p>Datatypes are used by RDF in the representation of values such
    as integers, floating point numbers and dates.</p>
		<p>RDF uses the datatype abstraction defined by XML Schema Part 2:
    Datatypes [<a href="#ref-xml-schema2">XML-SCHEMA2</a>], and may be used with any datatype definition that conforms to this abstraction, even if not actually defined in terms of XML Schema.</p>
		<p>A <dfn><a id="dfn-datatype-mapping" name=
    "dfn-datatype-mapping">datatype mapping</a></dfn> is a set of pairs
    whose first element belongs to the <dfn><a id="dfn-lexical-space"
    name="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 <cite>lexical space</cite> is paired with
      (maps to) exactly one member of the <cite>value
      space</cite>.</li>

      <li>Each member of the <cite>value space</cite> may be paired with any
      number (including zero) of members of
      the <cite>lexical space</cite> (lexical
      representations for that value).</li>
    </ul>

    <p>With one exception, the datatypes used in RDF have a
    <var><cite>lexical space</cite></var> consisting of a set of
    strings. The exception is <a href=
    "#dfn-rdf-XMLLiteral" class="code">rdf:XMLLiteral</a>, whose
    lexical space also includes pairs of strings and language
    identifiers. The value obtained through its datatype mapping may
    depend on the language identifier.</p>

    <p>For example, the datatype 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">Datatype 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</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>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.</p>

    <p>The defining authority of a URI
    which identifies a datatype is responsible for specifying the
    datatype's lexical space, value space and datatype mapping.</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 arc.</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 identifier. This should 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, a
      datatype URI and an optional language identifier. It denotes the
      member of the identified datatype's value space obtained by
      applying the datatype mapping to the literal string.</li>
    </ul>

    <p>Continuing the example from <a href="#section-Datatypes">section
    3.3</a>, the typed literals which 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>Datatype 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>


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


    <p>Some simple facts indicate a relationship between
       two objects.
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 objects.


     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 5 from the
    [<a href=
    "#ref-rdf-primer">RDF-PRIMER</a>]:

</p>


            <div class="figure">
              <img src="http://www.w3.org/TR/2002/WD-rdf-primer-20021111/fig5-full" alt=
              "Using a Blank Node" width="100%" /><br />
               RDF Primer Figure 5: 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">ZIP</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). The expressive
power of RDF corresponds to the existential-conjunctive (EC) subset of
first order logic [<a href=
    "#ref-sowa">Sowa</a>]. </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/rdf-mt/#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>

    <h3><a id="section-URIspaces" name="section-URIspaces">3.7 RDF Core
    URI Vocabulary and Namespaces (Normative)</a></h3>

    <p>RDF uses URIs to identify resources and properties. Certain URIs
    are reserved for use by RDF, and may not be used for any purpose
    not sanctioned the RDF specifications. Specifically, URIs with the
    following leading substrings are reserved for RDF core
    vocabulary:</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, these URI prefix strings
    correspond to XML namespaces [<a href="#ref-namespaces">XML-NS</a>]
    associated with the RDF core vocabulary terms.</p>

    <div class="note">
      <p><strong>Note:</strong> these namespace URIs are the same as those used in
      earlier RDF documents [<a href="#ref-rdf-ms">RDF-MS</a>] [<a
      href="#ref-rdf-schema">RDF-SCHEMA</a>].</p>

      <p class="todo">[[[<b>NOTE FOR&nbsp;REVIEWERS:</b> Some terms in
      these namespaces have been deprecated, some have been added, and
      some RDF schema terms have had their meaning changed. We invite
      community feedback regarding the relative costs of adopting these
      changes under the old namespace URIs vs creating new URIs for
      this revision of RDF.]]]</p>
    </div>

    <p>Vocabulary terms in the <span class="code">rdf:</span> namespace
    are listed in <a href=
    "http://www.w3.org/TR/rdf-syntax-grammar/#section-Namespace">section
    5.1</a> of the RDF syntax specification [<a href=
    "#ref-rdf-syntax">RDF-SYNTAX</a>].</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 id="section-Meaning" name="section-Meaning">4. Meaning of
    RDF (Normative)</a></h2>

    <p>There are two aspects to the meaning of an RDF graph. There is
    the formal meaning as determined by the RDF semantics
[<a href=
    "#ref-rdf-semantics">RDF-SEMANTICS</a>].
This determines, with
    mathematical precision, the conclusions that can
    logically  be drawn from an RDF graph. There is also the social
    meaning of the graph. It is the social meaning that affects what it
    means to people and how it interacts with human social institutions
    such as our systems of law.</p>

    <h3><a id="section-AssertedForm" name="section-AssertedForm">4.1
    Asserted and Non-asserted Forms</a></h3>

    <p>RDF/XML expressions, i.e. encodings of RDF graphs, can be used
    to make claims or assertions about the 'real' world. Such
    expressions are said to be <dfn><a id="dfn-asserted" name=
    "dfn-asserted">asserted</a></dfn>.</p>

    <p>Not every RDF/XML expression is asserted.
    Some may convey
    meaning that is partly determined by the circumstances in which
    they are used. For example, in English, a statement "I don't
    believe that George is a clown" contains the words "George is a
    clown", which, considered in isolation, has the form of an
    assertion that George exhibits certain comic qualities. However,
    considering the whole sentence, no such assertion is considered to
    be made.</p>

    <h3><a id="section-Social" name="section-Social">4.2 Social
    Meaning</a></h3>

    <p>When an RDF graph is asserted in the Web, its publisher is
    saying something about their view of the world. Such an assertion
    should be understood to carry the same social import and
    responsibilities as an assertion in any other format. A combination
    of social (e.g. legal) and technical machinery (protocols, file
    formats, publication frameworks) provide the contexts that fix the
    intended meanings of the vocabulary of some piece of RDF, and which
    distinguish assertions from other uses (e.g. citations, denials or
    illustrations).</p>

    <p>The technical machinery includes protocols for transferring
    information (e.g. HTTP, SMTP) and file formats for encapsulating
    and labelling information (e.g. MIME, XML). A media type,
<span
    class="code">application/rdf+xml</span> [<a href=
    "#ref-rdf-mime-type">RDF-MIME-TYPE</a>]
indicates the use of
    RDF/XML as distinct from some other XML that happens to look like
    RDF. Issuing an HTTP GET&nbsp;request and obtaining data with a
    "200 OK" response code is a technical indication that the received
    data was published at the request URI; but data received with a
    "404 Not found" response cannot be considered to be similarly
    published information.</p>

    <p>The social machinery includes the form of publication:
    publishing some unqualified statements on one's World Wide Web home
    page would generally be taken as an assertion of those statements.
    But publishing the same statements with a qualification, such as
    "here are some common myths", or as part of a rebuttal, would
    likely not be construed as an assertion of the truth of those
    statements. Similar considerations apply to the publication of
    assertions expressed in RDF.</p>

   <p>
An RDF graph may contain "defining information" that is opaque to
logical reasoners. This information may be used by human interpreters of
RDF information, or programmers writing software to perform specialized
forms of deduction in the Semantic Web.</p>

    <h3><a name="section-authority" id=
    "section-authority">4.3 Authoritative Definition of Terms</a></h3>
<p>
The social conventions surrounding use of RDF assume that any RDF URI
reference gains its meaning from some defining individual, organization or
context.  This applies most notably to RDF predicate URI references.
</p>
<p>
These social conventions are rooted in the URI specification [<a href=
        "#ref-uris">URI</a>]
 and
registration procedures [<a href=
        "#ref-uri-reg">URI-REG</a>].  A URI scheme registration refers to a
specification of the detailed syntax and interpretation for that scheme,
from which the defining authority for a given URI may be deduced.  In the
case of http: URIs, the defining specification is the HTTP protocol
specification [<a href=
        "#ref-http">HTTP</a>], which specifies how to use the HTTP protocol to
obtain a resource representation from the host named in the URI;  thus, the
owner of the indicated DNS domain controls (observable aspects of) the
URI's meaning.
</p>
<p>
Thus, the choice of terms used in published RDF is significant in
determining its meaning, through reference to definitions asserted by the
defining authorities for those terms.
</p>
<p>
For important documents, the use of third-party vocabulary should be restricted
 to terms defined by trustworthy parties (e.g. recognized standards bodies
or reputable organizations),
 or that otherwise have socially well-established meanings.
</p>
<p>However,
 even when a URI reference can be dereferenced as an RDF/XML
document, it's use within an
asserted RDF graph does not
implicitly assert the contents of the
referenced document.
</p>


    <h3><a id="section-Interaction" name="section-Interaction">4.4
    Interaction Between Social and Formal Meaning </a></h3>


    <p>Human publishers of RDF content commit themselves to the
    mechanically-inferred social obligations.
</p>

    <p>The meaning of an RDF document includes
    the social meaning, the formal meaning, and
the social meaning of the formal entailments.
The assertion of an RDF graph <var>G</var>,
when <var>G</var> logically entails <var>G'</var>,
includes the implicit assertion of <var>G'</var>.
The implied assertion of <var>G'</var> should be interpreted
using the same social
    conventions that are  reasonably used to
    interpret the assertion of <var>G</var>.</p>
<!--
   <p>The logical entailment intended with content of
media type
<span
    class="code">application/rdf+xml</span> [<a href=
    "#ref-rdf-mime-type">RDF-MIME-TYPE</a>]
is that defined in the RDF Semantics
[<a href=
    "#ref-rdf-semantics">RDF-SEMANTICS</a>],
as <a href="http://www.w3.org/TR/rdf-mt/#XSD-entailment">XSD entailment</a>,
i.e. respecting the RDF vocabulary, the RDFS vocabulary and
the XML Schema datatypes.</p>

  <p>Information within such content, or
the use of a different media type, may indicate
the use of a
<a href="http://www.w3.org/TR/rdf-mt/#dfn-semantic-extension">semantic extension</a> to RDF. When such an extension is indicated, this usually
indicates that the stronger formal entailment associated with that
extension is intended as part of the meaning of the RDF.</p>


    <p>The social conventions surrounding use of RDF include
of RDF include the idea that each
URI is associated with some defining authority or context, from which it
derives its meaning.  See <link>section 2.4.4</link> for further discussion
of this idea.
</p>

]]


the idea
    that each URI 'belongs to' somebody who has authority and
    responsibility for defining its meaning. The social conventions are
    rooted in the URI specification [<a href="#ref-uris">RFC2396</a>]
    and registration procedures [<a href="#ref-uri-reg">RFC2717</a>]. A
    URI scheme registration refers to a specification of the detailed
    syntax and interpretation for that scheme, from which the defining
    authority for a given URI may be deduced. In the case of
    <var>http:</var> URIs, the defining specification is the HTTP
    protocol specification [RFC2616], which obtains a resource
    representation from the host named in the URI; thus, the owner of
    the host's DNS domain controls (observable aspects of) the URI's
    meaning.</p>

    <p>Publication of
    RDF, when considered as a social act, constitutes a publication of
    some content that is defined by whatever normal <span class=
    "expression">social</span> conditions are used by the publishers of
    any terms in the RDF to define the meanings of those terms, even if
    those meanings and definitions are not accessible to the formal
    semantics of RDF; and, moreover, those meanings are preserved under
    any formally sanctioned inference processes. </p>
-->

    <h3><a id="section-InteractionExample" name=
    "section-InteractionExample">4.5 Example (Informative)</a></h3>

    <p>Imagine two websites publishing the following RDF:</p>

    <table border="0" cellspacing="2" cellpadding="4" summary=
    "This table shows RDF triples found in two different websites:
     concerning the terms A:Clown and B:Comic.">
      <tr>
        <td colspan="3" valign="top">(A) <span class=
        "expression">http://insult.example.com/lexicon#<br />
        </span> asserts the following, and this is all that one can
        find on the website about that term:</td>
      </tr>

      <tr>
        <td class="code" valign="top">A:Clown</td>

        <td class="code" valign="top">rdf:type</td>

        <td class="code" valign="top">rdfs:Class .</td>
      </tr>

      <tr>
        <td class="code" valign="top">A:Clown</td>

        <td class="code" valign="top">rdfs:comment</td>

        <td class="code" valign="top">"A class of foolish people, whose
        pronouncements are probably ill-considered and not to be taken
        seriously" .</td>
      </tr>

      <tr>
        <td colspan="3" valign="top"><br />
         (B) <span class=
        "expression">http://AngloSaxon.example.org/lexicon#</span><br />

         asserts:</td>
      </tr>

      <tr>
        <td class="code" valign="top">B:Comic</td>

        <td class="code" valign="top">rdf:subClassOf</td>

        <td class="code" valign="top">
        &lt;http://insult.example.com/lexicon#Clown&gt; .</td>
      </tr>
</table>
<p>
Imagine also a third, using the vocabulary previously defined
by the first two.</p>
 <table border="0" cellspacing="2" cellpadding="4" summary=
    "This table shows an RDF triple  found in a third website.">
      <tr>
        <td colspan="3" valign="top">
          <p><br />
           (C) <span class=
          "expression">http://skunk.example.org/</span><br />
           asserts the following, assuming that <span class=
          "expression">C:JohnSmith</span> is understood to refer to
          some particular person:</p>
        </td>
      </tr>

      <tr>
        <td class="code" valign="top">C:JohnSmith</td>

        <td class="code" valign="top">rdf:type</td>

        <td class="code" valign="top">
        &lt;http://AngloSaxon.example.org/lexicon#Comic&gt; .</td>
      </tr>
    </table>

    <p>Now, it follows by the formal RDF model theory that these three
    together entail:</p>

    <table border="0" cellspacing="2" cellpadding="4" summary=
    "This table shows a formal entailment of the two previous tables.">
      <tr>
        <td class="code" valign="top">C:JohnSmith</td>

        <td class="code" valign="top">rdf:type</td>

        <td class="code" valign="top">
        A:Clown .</td>
      </tr>
      <tr>
        <td class="code" valign="top">&lt;A:Clown&gt;</td>

        <td class="code" valign="top">rdfs:comment</td>

        <td class="code" valign="top">"A class of foolish people, whose
        pronouncements are probably ill-considered and not to be taken
        seriously" .</td>
      </tr>
    </table>

<p>Given this formal entailment, the
social context of
<a href="http://www.w3.org/TR/2002/WD-rdf-schema-20021112/#ch_comment"><span class=
          "expression">rdfs:comment</span></a>
is understood by referring
to the
    [<a href="#ref-rdf-vocabulary">RDF-VOCABULARY</a>] which says it provides:
"a human-readable description of a resource".
Thus, the person identified as <span class=
    "expression">C:JohnSmith</span> might reasonably consider himself
to be
    insulted.
</p>

<p>Moreover, since the publishers of the third Web site <span class=
          "expression">http://skunk.example.org/</span>
link <span class=
    "expression">C:JohnSmith</span> to the vocabulary
 previously defined to be insulting, it is they who have insulted
<span class=
    "expression">C:JohnSmith</span>.</p>

<!--
    <p>which Why? Not because of the RDF model theory, which merely says
    he is in some class about which nothing can be <em>formally</em>
    inferred. However, the <span class="expression">rdfs:comment</span>
    associated with that class name by the owner of that name provides
    the insulting content, <em>in the social context of Web
    publication</em>, even though it cannot be formally inferred via
    the RDF inference rules.</p>

    <p>But who has insulted the identified person? A merely defined the
    term; B does not mention him in particular, so even A and B
    together do not constitute a personal insult. And C might argue
    that although he refers to the person, he only asserts that he is a
    comic, which is not in itself grounds for a libel suit. However,
    one could reasonably claim that C is to blame, since C uses not a
    generic term 'Comic', but a particular URI reference which is
    defined by its owner (B) in a way which is clearly insulting, since
    B in turn explicitly refers to, and uses, the term defined by A.
    Thus, C's use of a B-defined term suggests a clear intent by C to
    convey a meaning defined by B, by virtue of a definition by A,
    which is insulting.</p>

    <p>By using the specific name <span class=
    "expression">http://AngloSaxon.example.org/lexicon#Comic</span>
    instead of some term defined in, say, a glossary of job
    descriptions, B has explicitly removed his use of the term 'Clown'
    from any formal connection with people who are entertainers. In
    order to succeed in his probable intent of making a generic slander
    against these people, B should have used a term that was defined by
    someone else, such as:</p>

    <table width="100%" border="0" cellspacing="2" cellpadding="4"
    summary=
    "This table shows the triple: http://www.entertainers.com/glossary#Comic rdfs:subClassOf http://insult.com/lexicon#Clown.">
      <tr>
        <td class="code" colspan="3" valign="top">
        &lt;http://entertainers.example.com/glossary#Comic&gt;<br />
         rdfs:subClassOf
        &lt;http://insult.example.com/lexicon#Clown&gt; .</td>
      </tr>
    </table>

    <p>and then if C had also used this first URI reference, then in
    spite of a similar formal inference chain generating the insulting
    conclusion about <span class="expression">C:JohnSmith</span>, there
    would be nobody to sue, since now C would indeed have simply made a
    harmless observation about his occupation, and B's assertion, while
    indeed arguably offensive, makes no reference to him in
    particular.</p>
-->


    <h2><a id="section-XMLLiteral" name="section-XMLLiteral">5. XML
    Content within an RDF Graph (Normative)</a></h2>

    <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,
    <span class="code">rdf:XMLLiteral</span>.</p>

    <p>As part of the definition of this datatype, an ancillary
    definition is used.</p>

    <p>The <em>XML document corresponding to</em> a pair <var>( str,
    lang )</var> is formed as follows:</p>

    <div class="block">
      <p>Concatenate the five strings:</p>

      <ol>
        <li><span class="code">"&lt;rdf-wrapper xml:lang='"</span></li>

        <li><var>lang</var></li>

        <li><span class="code">"'&gt;"</span></li>

        <li><var>str</var></li>

        <li><span class="code">"&lt;/rdf-wrapper&gt;"</span></li>
      </ol>

      <p>Encode the resulting Unicode string in UTF-8 to form the
      corresponding XML document.</p>

      <p>No escaping is applied. The choice of <span class="code">rdf-wrapper</span>
      is fixed but arbitrary.</p>
    </div>

    <p>The <em>XML document corresponding to</em> a string
    <var>str</var> is formed as the XML document corresponding to the
    pair <var>(str, "")</var>.</p>

    <p>Using this, the datatype <dfn><a id="dfn-rdfs-XMLLiteral" name= "dfn-rdfs-XMLLiteral" > </a><a id="dfn-rdf-XMLLiteral" name= "dfn-rdf-XMLLiteral" class="code">rdf:XMLLiteral</a></dfn> is
    defined as follows.</p>

    <dl>
      <dt>The datatype URI</dt>

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

      <dt>The value space</dt>

      <dd>
        is the set of all XML documents that:

        <ul>
          <li>Have root element tag:
          <span class="code">&lt;rdf-wrapper&gt;</span></li>

          <li>Have no attributes on the root element other than
          <span class="code">xml:lang</span></li>

          <li>are <a href=
          "http://www.w3.org/TR/2001/REC-xml-c14n-20010315#Terminology">
          Canonical XML</a> [<a href="#ref-XML-C14N">XML-C14N</a>]
          (with comments).</li>
        </ul>
      </dd>

      <dt>The lexical space</dt>

      <dd>contains all pairs <var>( string, lang )</var> where
      <var>lang</var> is any language identifier [<a href=
      "#ref-rfc-3066">RFC-3066</a>] in lowercase, and
      <span class="code">string</span> is well-balanced, self-contained XML element
      content [<a href="#ref-xml">XML</a>], for which the XML document
      corresponding to the pair is a <a href=
      "http://www.w3.org/TR/2000/REC-xml-20001006#sec-well-formed">well-formed
      XML document</a> <a href="#ref-xml">[XML]</a> that also conforms
      to <a href=
      "http://www.w3.org/TR/1999/REC-xml-names-19990114/">XML
      Namespaces</a> <a href="#ref-namespaces">[XML-NS]</a>.</dd>

      <dd>also contains all strings <span class="code">string</span> which are
      well-balanced, self-contained XML element content [<a href=
      "#ref-xml">XML</a>], and for which the corresponding XML document
      is a <a href=
      "http://www.w3.org/TR/2000/REC-xml-20001006#sec-well-formed">well-formed
      XML document</a> <a href="#ref-xml">[XML]</a> that also conforms
      to <a href=
      "http://www.w3.org/TR/1999/REC-xml-names-19990114/">XML
      Namespaces</a> <a href="#ref-namespaces">[XML-NS]</a>.</dd>

      <dt>The mapping</dt>

      <dd>is defined as the function that maps a pair or string to the
      <a href=
      "http://www.w3.org/TR/2001/REC-xml-c14n-20010315#Terminology">canonical
      form</a> [<a href="#ref-XML-C14N">XML-C14N</a>] (with comments)
      of the corresponding XML document.</dd>
    </dl>

      <p class="note"><strong>Reminder:</strong> All other datatypes have a lexical space
      being a set of strings, and a mapping which maps strings to
      values.</p>

      <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>

    <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 equality between RDF graphs. A
    definition of equality is needed to support the RDF Test Cases [<a
    href="#ref-rdf-tests">RDF-TESTS</a>] specification.</p>


    <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 <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
    Equality</a></h3>

    <p>Two RDF graphs <var>G</var> and <var>G'</var> are equal if there
    is a bijection <var>M</var> between the nodes of the two graphs,
    such that:</p>

    <ol>
      <li><var>M(lit)=lit</var> for all <a href=
      "#dfn-literal">RDF literals</a> <var>lit</var> which
      are nodes of either graph.</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 either graph.</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, there are the same number of blank nodes in the two graphs,
   and <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>is in Normal Form C [<a href="#ref-nfc">NFC</a>] and</li>

      <li>
        would produce a
valid URI character sequence (per RFC2396 [<a href=
        "#ref-uris">URI</a>], sections 2.1)
 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>Editors' Note:</strong> This section is in the scope of
      the <a href="http://www.w3.org/2001/tag/">TAG</a> issue
<a href="http://www.w3.org/2001/tag/ilist#IRIEverywhere-27">IRIEverywhere-27</a>.
      The editors are expecting a resolution
      of this issue during the last call period. This may result in updates
      to this section.</p>

      <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, and constrained to
      be in Unicode Normal Form C [<a href="#ref-nfc">NFC</a>] (for
      compatibility with [<a href="#ref-charmod">CHARMOD</a>]).</p>

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

    <ul>
      <li>The <dfn><a id="dfn-lexical-form" name=
      "dfn-lexical-form">lexical form</a></dfn> being a Unicode [<a
      href="#ref-unicode">UNICODE</a>] string in Normal Form C [<a
      href="#ref-nfc">NFC</a>].</li>

      <li>The <dfn><a id="dfn-language-identifier" name=
      "dfn-language-identifier">language identifier</a></dfn> as
      defined by [<a href="#ref-rfc-3066">RFC-3066</a>], normalized to
      lowercase.</li>

      <li>The <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>.</li>
    </ul>

    <p>The lexical form is present in all RDF literals; the language
    identifier and the datatype URI may be absent from an RDF
    literal.</p>

    <p>A <dfn><a id="dfn-plain-literal" name="dfn-plain-literal">plain literal</a></dfn> is one in which the datatype URI is absent.</p>

    <p>A <dfn><a id="dfn-typed-literal" name="dfn-typed-literal">typed literal</a></dfn> is one in which the datatype URI is present.</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 identifier, care must be
      taken not to confuse language with locale. The language
      identifier only relates to human language text. Presentational
      issues, how to best represent typed data to the end-user, should
      be addressed in end-user applications.</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 identifiers.</li>

      <li>The language identifiers of the two lexical forms 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 identifier) 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 datatype mapping associated with the datatype URI to
    the lexical form.
    Exceptionally, if the datatype is <a href=
    "#section-XMLLiteral" class="code">rdf:XMLLiteral</a> and the
    literal has a language identifier, then the datatype mapping is
    applied to the pair form by the lexical form and the language
    identifier.</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>syntacticly</em> ill-formed.</p>

    <p>A typed literal for which the datatype does not map the lexical
    form to a value is not syntacticly 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 is arbitrary.
</p>
<p>RDF makes no reference to any internal structure of blank nodes.</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, in an RDF graph, any RDF URI reference consisting of an
    absolute URI and a fragment identifier identifies the same thing as
    the fragment identifier does in an application/rdf+xml [<a href=
    "#ref-rdf-mime-type">RDF-MIME-TYPE</a>] 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) indicates a Web resource with 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 presumed to
      designate an RDF document.</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, 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 interpretation 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 an abstract idea, like Graham Klyne's car or a mythical
      Unicorn.</li>

      <li>thus, 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, 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.</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>-->

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

      <dd><i><a href=
      "http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/">RDF/XML
      Syntax Specification (Revised)</a></i>, Dave Beckett, World Wide
      Web Consortium, 8 November 2002 (work in progress). This version
      of the RDF/XML Syntax Specification (Revised) is
      http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/. The
      latest version is at <a href=
      "http://www.w3.org/TR/rdf-syntax-grammar/">http://www.w3.org/TR/rdf-syntax-grammar/</a>.</dd>

      <dt><a id="ref-rdf-semantics" name=
      "ref-rdf-semantics"></a>[RDF-SEMANTICS]</dt>

      <dd><cite><a href=
      "http://www.w3.org/TR/2002/WD-rdf-mt-20021112/">RDF Semantics</a></cite>,
      P. Hayes,  World Wide
      Web Consortium, 12 November 2002 (work in progress).
      This version of the RDF Semantics is
      http://www.w3.org/TR/2002/WD-rdf-mt-20021112/. The latest version
      is at <a
      href="http://www.w3.org/TR/rdf-mt/">http://www.w3.org/TR/rdf-mt/</a>.</dd>

      <dt><a id="ref-rdf-vocabulary" name=
      "ref-rdf-vocabulary"></a>[RDF-VOCABULARY]</dt>

      <dd><i><a href="http://www.w3.org/TR/2002/WD-rdf-schema-20021112/">RDF Vocabulary
      Description Language 1.0: RDF Schema</a></i>, Dan Brickley, R.V.
      Guha, World Wide Web Consortium, April 2002 (work in progress).
      This version of the RDF Vocabulary
      Description Language  is http://www.w3.org/TR/2002/WD-rdf-schema-20021112/.
      The latest version is at <a href=
      "http://www.w3.org/TR/rdf-schema/">http://www.w3.org/TR/rdf-schema/</a>.</dd>

      <dt><a id="ref-rdf-mime-type" name=
      "ref-rdf-mime-type"></a>[RDF-MIME-TYPE]</dt>

      <dd><i><a href=
      "http://www.ietf.org/internet-drafts/draft-swartz-rdfcore-rdfxml-mediatype-01.txt">
      Application/rdf+xml Media Type Registration</a></i>, A. Swartz,
      IETF Internet Draft, March 2002 (work in progress). Version
      available at <a href=
      "http://www.ietf.org/internet-drafts/draft-swartz-rdfcore-rdfxml-mediatype-01.txt">
      http://www.ietf.org/internet-drafts/draft-swartz-rdfcore-rdfxml-mediatype-01.txt</a>.</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-http" name="ref-http"></a>[HTTP]</dt>

      <dd><cite><a href="http://www.isi.edu/in-notes/rfc2616.txt">RFC
      2616 - Hypertext Transfer Protocol -- HTTP/1.1</a></cite>,
R. Fielding, UC Irvine, J. Gettys, J. Mogul, H. Frystyk, L. Masinter,
P. Leach,
T. Berners-Lee,
      IETF, August 1998. This document is
      http://www.isi.edu/in-notes/rfc2616.txt.</dd>

      <dt><a id="ref-uri-reg" name="ref-uri-reg"></a>[URI-REG]</dt>

      <dd><cite><a href="http://www.isi.edu/in-notes/rfc2717.txt">RFC
      2717 - Registration Procedures for URL Scheme Names</a></cite>,
      R. Petke and I. King, IETF, November 1999. This document is
      http://www.isi.edu/in-notes/rfc2717.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-C14N" name="ref-XML-C14N"></a>[XML-C14N]</dt>

      <dd><a href=
      "http://www.w3.org/TR/2001/REC-xml-c14n-20010315">Canonical
      XML.</a> J. Boyer. W3C Recommendation, March 2001.</dd>

      <dd>Available at <a href=
      "http://www.w3.org/TR/2001/REC-xml-c14n-20010315">http://www.w3.org/TR/2001/REC-xml-c14n-20010315</a></dd>

      <dd>Available at <a href=
      "http://www.ietf.org/rfc/rfc3076.txt">http://www.ietf.org/rfc/rfc3076.txt</a></dd>
<!--
      <dt><a id="ref-keywords" name="ref-keywords"></a>[KEYWORDS]</dt>

      <dd><cite><a href="http://www.ietf.org/rfc/rfc2119.txt">RFC 2119
      - Key words for use in RFCs to Indicate Requirement
      Levels</a></cite>, S. Bradner, IETF. March 1997. This document is
      http://www.ietf.org/rfc/rfc2119.txt. <span class="todo">[[[Is
      this used?]]]</span></dd>

      <dt><a id="ref-rfc3023" name="ref-rfc3023"></a>[RFC-3023]</dt>

      <dd><cite><a href="http://www.ietf.org/rfc/rfc3023.txt">RFC 3032
      - XML Media Types</a></cite>, M. Murata, S. St.Laurent, D.Kohn,
      IETF, January 2001. This document is
      http://www.ietf.org/rfc/rfc3023.txt.</dd>
-->
      <dt><a id="ref-xml-schema2" name=
      "ref-xml-schema2"></a>[XML-SCHEMA2]</dt>

      <dd><cite><a href="http://www.w3.org/TR/xmlschema-2/">XML Schema
      Part 2: Datatypes - W3C Recommendation</a></cite>, World Wide Web
      Consortium, 2 May 2001.</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/2002/WD-rdf-testcases-20021112/">RDF Test
      Cases</a></cite>, Jan Grant and Dave Beckett, Editors. Work in
      progress. World Wide Web Consortium, 29 April 2002. This version
      of the RDF Test Cases is
      <span>http://www.w3.org/TR/2002/WD-rdf-testcases-20021112/</span>.
      The latest version of the RDF Test Cases is at <a href=
      "http://www.w3.org/TR/rdf-testcases/">http://www.w3.org/TR/rdf-testcases/</a>.</dd>


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

      <dd><cite><a href=
      "http://www.w3.org/TR/2002/WD-rdf-primer-20020426/">RDF
      Primer</a></cite>, F. Manola, E. Miller, Editors, World Wide Web
      Consortium W3C Working Draft, work in progress, 26 April 2002.
      This version of the RDF Primer is
      http://www.w3.org/TR/2002/WD-rdf-primer-20020426/. The <a href=
      "http://www.w3.org/TR/rdf-primer/">latest version of the RDF
      Primer</a> is 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/2002/WD-charmod-20020220/">Character Model
      for the World Wide Web 1.0</a></cite>, M. D&uuml;rst, F. Yergeau,
      R. Ishida, M. Wolf, A. Freytag, T Texin, Editors, World Wide Web
      Consortium Working Draft, work in progress, 20 February 2002.
      This version of the Character Model is
      http://www.w3.org/TR/2002/WD-charmod-20020220/. 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/xml11/">Extensible Markup
      Language (XML) 1.1</a></cite>, John Cowan, Editor. World Wide Web
      Consortium Working Draft 25 April 2002. <i>(Work in
      progress)</i></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/xml-names11/">Namespaces
      in XML 1.1</a></cite>, Tim Bray, Dave Hollander, Andrew Layman,
      Richard Tobin, Editors. World Wide Web Consortium Working Draft 5
      September 2002. <i>(Work in progress)</i></dd>

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

      <dd><i><a href="http://www.w3.org/TR/xml-infoset/">XML
      Information Set</a></i>, John Cowan and Richard Tobin, W3C
      Recommendation, 24 October 2001. This document is
      http://www.w3.org/TR/xml-infoset/.</dd>
<!--
      <dt><a id="ref-xmlschema0" name=
      "ref-xmlschema0"></a>[XML-SCHEMA0]</dt>

      <dd><cite><a href="http://www.w3.org/TR/xmlschema-0/">XML Schema
      Part 0: Primer - W3C Recommendation</a></cite>, World Wide Web
      Consortium, 2 May 2001.</dd>

      <dt><a id="ref-xmlschema1" name=
      "ref-xmlschema1"></a>[XML-SCHEMA1]</dt>

      <dd><cite><a href="http://www.w3.org/TR/xmlschema-1/">XML Schema
      Part 1: Structures - W3C Recommendation</a></cite>, World Wide
      Web Consortium, 2 May 2001.</dd>
-->

      <dt><a id="ref-owl" name="ref-owl"></a>[OWL]</dt>

      <dd><a href=
      "http://www.w3.org/TR/2002/WD-owl-ref-20020729/"><i>OWL Web
      Ontology Language 1.0 Reference</i></a>, Mike Dean, Dan Connolly,
      Frank van Harmelen, James Hendler, Ian Horrocks, Deborah L.
      McGuinness, Peter F. Patel-Schneider, and Lynn Andrea Stein. W3C
      Working Draft 29 July 2002. Latest version is available at <a
      href=
      "http://www.w3.org/TR/owl-ref/">http://www.w3.org/TR/owl-ref/</a>.</dd>

      <dt><a id="ref-sowa" name="ref-sowa"></a>[SOWA]</dt>

      <dd><i>Knowledge Representation: Logical, Philosophical and
      Computational Foundations</i>, John F. Sowa, Brookes/Cole, 2000.
      ISBN 0-534-94965-7.</dd>

<!--
      <dt><a id="ref-notation3" name=
      "ref-notation3"></a>[NOTATION3]</dt>

      <dd>Tim Berners-Lee, DesignIssues note on N3, ...</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-rdf-schema" name=
      "ref-rdf-schema"></a>[RDF-SCHEMA]</dt>

      <dd><i><a href="http://www.w3.org/TR/2000/CR-rdf-schema-20000327/">
Resource
      Description Framework (RDF) Schema Specification 1.0</a></i>, Dan
      Brickley and R. V. Guha, W3C Candidate Recommendation, 27 March
      2000. This document is http://www.w3.org/TR/2000/CR-rdf-schema-20000327/.</dd>
      <!--
                  <dt><a id="ref-tap-rbd" name="ref-tap-rbd"></a>[TAP-RBD]</dt>
                  <dd><i><a href="http://www.alpiri.org/protocol/rbd.html">Reference
                  by Description</a></i>, R. V. Guha: <a
                  href="http://www.alpiri.org/protocol/rbd.html">http://www.alpiri.org/protocol/rbd.html</a>.
                  (Related to the TAP project: <a
                  href="http://tap.stanford.edu/">http://tap.stanford.edu/</a>).</dd>
                  -->
    </dl>
		<hr />
		<div class="metadata">
      <p><a href="metadata.rdf"><img
      src="rdf_meta.gif" alt="RDF/XML Metadata" /></a></p>
    </div>
  </body>
</html>