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- <title>RDF 1.1 Concepts and Abstract Syntax</title>
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- <body>
-
-<section id="abstract">
- <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 IRIs.</p>
-</section>
-
-
-<section id="section-Introduction">
- <h2>Introduction</h2>
-
- <p class="issue">This document reflects current progress of the RDF Working
- Group towards updating the
- <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">2004
- version of <em>RDF Concepts and Abstract Syntax</em></a>. The
- editors expect to work on a number of issues, some of which are
- listed in boxes like this throughout the document.</p>
-
- <p>The Resource Description Framework (RDF) is a framework for
- representing information in the Web.</p>
-
- <p>This document defines an abstract syntax 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
- [[XML-INFOSET]]. It also includes discussion of design goals,
- key concepts, datatyping, character normalization
- and handling of IRIs.</p>
-
- <p>Normative documentation of RDF falls into the following
- areas:</p>
-
- <ul>
- <li>XML serialization syntax [[!RDF-SYNTAX-GRAMMAR]],</li>
-
- <li>formal semantics [[!RDF-MT]], and</li>
-
- <li>this document (sections 4, 5, 6 and 7).</li>
- </ul>
-
- <p class="issue">This document was written when RDF/XML was the
- only normative syntax. Now it is just one of many syntaxes and
- it should be de-emphasized accordingly. There is no reason why
- it should be a normative reference in this document.</p>
-
- <p>The framework is designed so that vocabularies can be layered.
-The RDF and RDF vocabulary definition (RDF schema)
-languages
- [[RDF-SCHEMA]] are the first
- such vocabularies.
-
- Others (cf. OWL [[OWL-REF]] and
- the applications mentioned in the primer
- [[RDF-PRIMER]]) are in development.</p>
-</section>
-
-
-<section id="conformance"></section>
-
-
-<section id="section-Overview" class="informative">
- <h2>Motivations and Goals</h2>
-
- <p class="issue">Does this section add value?</p>
-
- <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>
-
-<section id="section-motivation">
- <h3>Motivation</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>
-</section>
-
-
-<section>
- <h3 id="section-design-goals">Design Goals</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 IRI-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>
-
-
-<section id="section-simple-data-model">
- <h4>A Simple Data Model</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">The term “model” used here in “data model” has a
- completely different sense to its use in the term “model theory”.
- See [[!RDF-MT]]
- for more information about “model theory” as used in the literature of mathematics and logic.</p>
-</section>
-
-
-<section id="section-formal-semantics">
- <h4>Formal Semantics and Inference</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>
-</section>
-
-
-<section id="section-extensible-vocab">
- <h4>Extensible IRI-based Vocabulary</h4>
-
- <p>The vocabulary is fully extensible, being based on IRIs.
- IRIs 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>
-</section>
-
-
-<section id="section-xml-serialization">
- <h4>XML-based Syntax</h4>
-
- <p>RDF has a recommended XML serialization form [[!RDF-SYNTAX-GRAMMAR]], which can be used to encode the
- data model for exchange of information among applications.</p>
-</section>
-
-
-<section id="section-use-xsd">
- <h4>Use XML Schema Datatypes</h4>
-
- <p>RDF can use values represented according to XML schema datatypes
- [[!XMLSCHEMA-2]], thus assisting the
- exchange of information between RDF and other XML applications.</p>
-</section>
-
-
-<section id="section-anyone">
- <h4>Anyone Can Make Statements About Any Resource</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>
-</section>
-
-</section>
-
-</section>
-
-
-<section id="section-Concepts" class="informative">
- <h2>RDF Concepts</h2>
-
- <p class="issue">This section is quite redundant with later normative sections and the RDF Primer.</p>
-
- <p>RDF uses the following key concepts:</p>
-
- <ul>
- <li>Graph data model</li>
-
- <li>IRI-based vocabulary</li>
-
- <li>Datatypes</li>
-
- <li>Literals</li>
-
- <li>XML serialization syntax</li>
-
- <li>Expression of simple facts</li>
-
- <li>Entailment</li>
- </ul>
-
-
-<section id="section-data-model">
- <h3>Graph Data Model</h3>
-
- <p>The underlying structure of any expression in RDF is a
- collection of triples, each consisting of a subject, a
- predicate and an object. A set of such triples is called an RDF
- graph (defined more formally in
-<a href="#section-Graph-syntax">section 6</a>). This can be
- illustrated by a node and directed-arc diagram, in which each
- triple is represented as a node-arc-node link (hence the term
- “graph”).</p>
-
- <div class="figure">
- <img src="Graph-ex.gif" alt="image of the RDF triple comprising (subject, predicate, object)" />
- </div>
-
- <p>Each triple represents a statement of a relationship between
- the things denoted by the nodes that it links. Each triple has
- three parts:</p>
- <ol>
- <li>a <a>subject</a>,</li>
- <li>an <a>object</a>, and</li>
- <li>a <a>predicate</a> (also called a
- <a>property</a>) that denotes a
- relationship.</li>
- </ol>
- <p>The direction of the arc is significant: it always points
- toward the object.</p>
- <p>The <a title="node">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 [[!RDF-MT]].</p>
-</section>
-
-
-<section id="section-IRI-Vocabulary">
- <h3>IRI-based Vocabulary and Node Identification</h3>
-
- <p>A <a>node</a> may be an <a>IRI</a>, a <a>literal</a>,
- or <a title="blank node">blank</a> (having no separate form of identification).
- Properties are <a title="IRI">IRIs</a>.</p>
- <p>An <a>IRI</a> or <a>literal</a> used as a node identifies what
- that node represents. An IRI used as a predicate
- identifies a relationship between the things represented by the nodes it connects. A
- predicate IRI may also be a node in the graph.</p>
- <p>A <a>blank node</a> is a node that is
- not an IRI or a literal. In the RDF abstract syntax, a
- blank node is just a unique node that can be used in one or
- more RDF statements.</p>
- <p>A convention used by some linear representations of an RDF
- graph to allow several statements to use the same
- blank node is to use a <dfn>blank node
- identifier</dfn>, which is a local identifier that can be
- distinguished from all IRIs and literals. When graphs are
- merged, their blank nodes must be kept distinct if meaning is
- to be preserved; this may call for re-allocation of blank node
- identifiers. Note that such blank node identifiers are not part
- of the RDF abstract syntax, and the representation of triples
- containing blank nodes is entirely dependent on the particular
- concrete syntax used.</p>
-</section>
-
-
-<section name="section-Datatypes-intro">
- <h3>Datatypes</h3>
-
- <p>Datatypes are used by RDF in the representation of values such
- as integers, floating point numbers and dates.</p>
-
- <p>
-A datatype consists of a lexical space, a value space and a lexical-to-value
-mapping, see <a href="#section-Datatypes">section 5</a>.
-</p>
-
- <p>For example, the lexical-to-value mapping for the XML Schema datatype
- <var>xsd:boolean</var>, where each member of the value space
- (represented here as 'T' and 'F') has two lexical representations,
- is as follows:</p>
-
- <table border="1" cellpadding="5" summary=
- "A table detailing the xsd:boolean datatype.">
- <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>{<"true", T>, <"1", T>, <"0", F>,
- <"false", F>}</td>
- </tr>
- </table>
-
- <p>RDF predefines just one datatype <code><a>rdf:XMLLiteral</a></code>, used for
- embedding XML in RDF (see <a href="#section-XMLLiteral">section
- 5.1</a>).</p>
-
- <p>There is no built-in concept of numbers or dates or other common
- values. Rather, RDF defers to datatypes that are defined
- separately, and identified with <a title="IRI">IRIs</a>.
- The predefined XML Schema
- datatypes [[!XMLSCHEMA-2]] are expected
- to be widely used for this purpose.</p>
-
-
- <p>RDF provides no mechanism for defining new datatypes. XML Schema
- Datatypes [[!XMLSCHEMA-2]] provides an
- extensibility framework suitable for defining new datatypes for use
- in RDF.</p>
-</section>
-
-
-<section name="section-Literals">
- <h3> Literals</h3>
-
- <p><a title="literal">Literals</a> are used to identify values such as numbers and dates
- by means of a lexical representation. Anything represented by a
- literal could also be represented by an <a>IRI</a>, but it is often more
- convenient or intuitive to use literals.</p>
-
- <p>A literal may be the object of an RDF statement, but not the
- subject or the predicate.</p>
-
- <p>Literals may be <cite>plain</cite> or <cite>typed</cite> :</p>
-
- <ul>
- <li>A <a>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 [[!RDF-MT]], these plain literals are
- self-denoting.</li>
-
-
-
- <li>A <a>typed literal</a> is a string combined with a
- <a>datatype IRI</a>. It denotes the
- member of the identified datatype's value space obtained by
- applying the lexical-to-value mapping to the literal string.</li>
- </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"><xsd:boolean, "true"></td>
-
- <td align="center"><"true", T></td>
-
- <td align="center">T</td>
- </tr>
-
- <tr>
- <td align="center"><xsd:boolean, "1"></td>
-
- <td align="center"><"1", T></td>
-
- <td align="center">T</td>
- </tr>
-
- <tr>
- <td align="center"><xsd:boolean, "false"></td>
-
- <td align="center"><"false", F></td>
-
- <td align="center">F</td>
- </tr>
-
- <tr>
- <td align="center"><xsd:boolean, "0"></td>
-
- <td align="center"><"0", F></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.
-[[XHTML10]] 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 [[!NFC]]. This is motivated
-by [[CHARMOD]] particularly
-<a href="http://www.w3.org/TR/2003/WD-charmod-20030822/#sec-Normalization">section 4
-Early Uniform Normalization</a>.
-</p>
-
-</section>
-
-
-<section id="section-SimpleFacts">
- <h3>RDF Expression of Simple Facts</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 <code>rdf:type</code> property whose value corresponds
-to the table name.
-</p>
-
- <p>As an example, consider Figure 6 from the [[RDF-PRIMER]]:
-
-</p>
-
- <div class="figure">
- <img src="fig6may19" alt="Using a Blank Node" /><br />
- RDF Primer Figure 6: Using a Blank Node
- </div>
-
-
- <p>
-This information might correspond to a row in a table <code>"STAFFADDRESSES"</code>,
- with a primary key
-<code>STAFFID</code>,
- and additional columns
-<code>STREET</code>,
-<code>STATE</code>,
-<code>CITY</code> and
-<code>POSTALCODE</code>.
- </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 IRI-based vocabularies, RDF
- provides for expression of facts about arbitrary subjects; i.e.
- assertions of named properties about specific named things. An IRI
- 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 [[TAP-RBD]].
- -->
- </p>
-</section>
-
-
-<section id="section-Entailment">
- <h3>Entailment</h3>
-
- <p>The ideas on meaning and inference in RDF are underpinned by the
- formal concept of <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#entail">
-<cite>entailment</cite></a>, as
- discussed in the RDF
- semantics document [[!RDF-MT]].
-In brief, an RDF expression A is said to
-<dfn title="entailment">entail</dfn> another RDF 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>
-</section>
-
-</section>
-
-
-<section id="section-URIspaces">
- <h2>RDF Vocabulary IRI and Namespace</h2>
-
- <p>RDF uses <a title="IRI">IRIs</a> to identify resources
- and properties. Certain
- IRIs are given specific meaning by RDF. Specifically, IRIs
- with the following leading substring are defined by the RDF
- specifications:</p>
-
- <ul>
- <li><code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>
- (conventionally associated with namespace prefix <code>rdf:</code>)</li>
-<!--
- <li><code>http://www.w3.org/2000/01/rdf-schema#</code>
- (conventionally associated with namespace prefix <code>rdfs:</code>)</li>
--->
- </ul>
- <p>Used with the RDF/XML serialization, this IRI prefix
- string corresponds to XML namespace names [[!XML-NAMES]] associated with the RDF
- vocabulary terms.</p>
-
- <p class="note">This namespace name is the same
- as that used in the earlier RDF recommendation [[RDF-SYNTAX]].</p>
-
- <p>Vocabulary terms in the <code>rdf:</code>
- 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 [[!RDF-SYNTAX-GRAMMAR]]. 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 <code>rdfs:</code> namespace are defined in the RDF
- schema vocabulary specification [[RDF-SCHEMA]].</p>
--->
-</section>
-
-
-<section name="section-Datatypes">
- <h2>Datatypes</h2>
-
- <p class="issue">This section perhaps should discuss
- <a href="http://www.w3.org/TR/rdf-mt/#dtype_interp">the XSD datatype map</a>
- and <code><a href="http://www.w3.org/TR/rdf-plain-literal/">rdf:PlainLiteral</a></code>.</p>
-
-<p>
-The datatype abstraction used in RDF is compatible with
-the abstraction used in
-XML Schema Part 2:
- Datatypes [[!XMLSCHEMA-2]].</p>
-<p>
-A datatype consists of a lexical space, a value space and a lexical-to-value
-mapping.
-</p>
-<p>The <dfn>lexical space</dfn> of a datatype is a set of Unicode [[!UNICODE]] strings.</p>
-<p>
-The <dfn>lexical-to-value mapping</dfn> of a datatype is a set of pairs whose
-first element belongs to
-the <a>lexical space</a> of the datatype,
-and the second element belongs to the
- <dfn>value space</dfn> of the datatype:
-</p>
-<ul>
-<li>
-Each member of the lexical space is paired with (maps to) exactly one member
-of the value space.
-</li>
-<li>
-Each member of the value space may be paired with any number (including
-zero) of members of the lexical space (lexical representations for that
-value).
-</li>
-</ul>
-<p>
-A datatype is identified by one or more IRIs.
-</p>
-<p>
-RDF may be used with any datatype definition that conforms to this
-abstraction, even if not defined in terms of XML Schema.
-</p>
- <p>Certain XML Schema built-in datatypes are not suitable for use
- within RDF. For example, the
-<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#QName">QName</a>
-datatype requires a namespace declaration to be in scope during
- the mapping, and is not recommended for use in RDF.
- [[!RDF-MT]] contains a
-<a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#dtype_interp">more detailed discussion</a>
- of specific XML Schema built-in datatypes. </p>
-
-<div class="note">
-<p>When the datatype is defined using XML Schema:
-</p>
-<ul>
-<li>
-All values correspond to some lexical form, either using
-the lexical-to-value mapping of the datatype or if it is a union
-datatype with a lexical mapping associated with one of the member
-datatypes.
-</li>
-<li>
-XML Schema facets remain part of the datatype and are used by the XML
-Schema mechanisms that control the lexical space and the value space;
-however, RDF does not define a standard mechanism to access these facets.</li>
-
-<li>In [[XMLSCHEMA-1]],
-<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>
-
-
-<section id="section-XMLLiteral">
- <h3>XML Content within an RDF Graph</h3>
-
- <p class="issue">The canonicalization rules required for XML literals
- are quite complicated. Increasingly, RDF is produced and consumed in
- environments where no XML parser and canonicalization engine is
- available. A possible change to relax the requirements for the
- lexical space, while retaining the value space, is under discussion.
- This is <a href="http://www.w3.org/2011/rdf-wg/track/issues/13">ISSUE-13</a>.</p>
-
- <p>RDF provides for XML content as a possible literal value. This
- typically originates from the use of
- <code>rdf:parseType="Literal"</code> in the RDF/XML Syntax [[!RDF-SYNTAX-GRAMMAR]].</p>
-
- <p>Such content is indicated in an RDF graph using a typed literal
- whose datatype is a special built-in datatype
- <dfn>rdf:XMLLiteral</dfn>,
- defined as follows.</p>
-
-
- <dl>
- <dt><a name="XMLLiteral-uri" id="XMLLiteral-uri">An IRI for
-identifying this datatype</a></dt>
-
- <dd>is
- <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral</code>.</dd>
-
-
-
-
- <dt><a name="XMLLiteral-lexical-space" id="XMLLiteral-lexical-space">The lexical space</a></dt>
-
-<dd>is the set of all
-strings:
-<ul>
-<li>which are well-balanced, self-contained
-<a href="http://www.w3.org/TR/2000/REC-xml-20001006#NT-content">
-XML content</a>
-[[!XML10]];
-</li>
-<li>for which encoding as UTF-8
-[[!RFC2279]] 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>) [[!XML-EXC-C14N]];
-</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> [[!XML-NAMES]]</li>
-</ul>
-</dd>
-
-
- <dt><a name="XMLLiteral-value-space" id="XMLLiteral-value-space">The value space</a></dt>
-
- <dd>is a set of entities, called XML values, which is:
-<ul>
-<li>disjoint from the lexical space;</li>
-<li>disjoint from the value space of any other datatype that is not explicitly defined as a sub- or supertype of this datatype;</li>
-<li>disjoint from the set of Unicode character strings [[!UNICODE]];</li>
-<li>and in 1:1 correspondence with the lexical space.</li>
-</ul>
-</dd>
-
- <dt><a name="XMLLiteral-mapping" id="XMLLiteral-mapping">The lexical-to-value mapping</a></dt>
-
- <dd>
-is a one-one mapping from the lexical space onto the value space,
- i.e. it is both injective and surjective.
-</dd>
-
-
-
- </dl>
-
-
- <p class="note">Not all values of this datatype are compliant
- with XML 1.1 [[XML11]]. If compliance
- with XML 1.1 is desired, then only those values that are
-<a href="http://www.w3.org/TR/2002/CR-xml11-20021015/#sec2.13">fully
- normalized</a> according to XML 1.1 should be used.</p>
-
- <p class="note">XML values can be thought of as the
-[[XML-INFOSET]] or the [[XPATH]]
-nodeset corresponding to the lexical form, with an appropriate equality
-function.</p>
-
- <p class="note">RDF applications may use additional equivalence relations, such as
-that which relates an
-<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#string"><code>xsd:string</code></a>
-
-with an <code>rdf:XMLLiteral</code> corresponding to
-a single text node of the same string.</p>
-
-</section>
-
-</section>
-
-
-<section id="section-Graph-syntax">
- <h2>Abstract Syntax</h2>
-
- <p>This section defines the RDF abstract syntax. The RDF abstract
- syntax is a set of triples, called the RDF graph.</p>
-
- <p>This section also defines equivalence between RDF graphs. A
- definition of equivalence is needed to support the RDF Test Cases
- [[RDF-TESTCASES]] specification.</p>
-
-<p class="note">This <em>abstract</em> syntax is the
-syntax over which the formal semantics are defined.
-Implementations are free to represent RDF graphs in
-any other equivalent form. As an example:
-in an RDF graph,
-literals with datatype <tt>rdf:XMLLiteral</tt> can be represented
-in a non-canonical
-format, and canonicalization performed during the comparison between two
-such literals. In this example the comparisons may be
-being performed either between syntactic structures or
-between their denotations in the domain of discourse.
-Implementations that do not require any such comparisons can
-hence be optimized.
-</p>
-
- <p class="issue">The SPARQL WG proposed to add definitions for
- “RDF Term” and “Simple Literal”.</p>
-
-
-<section id="section-triples">
- <h3>RDF Triples</h3>
-
- <p>An <dfn>RDF triple</dfn> contains three components:</p>
-
- <ul>
- <li>the <dfn>subject</dfn>, which is an
- <a>IRI</a> or a <a>blank node</a></li>
-
- <li>the <dfn>predicate</dfn>, which is an <a>IRI</a></li>
-
- <li>the <dfn>object</dfn>, which is an <a>IRI</a>,
- a <a>literal</a> or a <a>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>property</dfn> of the triple.</p>
-</section>
-
-
-<section id="section-rdf-graph">
- <h3>RDF Graph</h3>
-
- <p>An <dfn>RDF graph</dfn> is a set of RDF triples.</p>
-
- <p>The set of <dfn title="node">nodes</dfn> of an RDF graph is the set of subjects and objects of
- triples in the graph.</p>
-</section>
-
-
-<section id="section-graph-equality">
- <h3>Graph Equivalence</h3>
-
- <p>Two <a title="RDF graph">RDF graphs</a> <var>G</var> and <var>G'</var> are equivalent if there
- is a bijection <var>M</var> between the sets of nodes of the two graphs,
- such that:</p>
-
- <ol>
- <li><var>M</var> maps blank nodes to blank nodes.</li>
- <li><var>M(lit)=lit</var> for all <a title="literal">RDF literals</a> <var>lit</var> which
- are nodes of <var>G</var>.</li>
-
- <li><var>M(uri)=uri</var> for all <a title="IRI">IRIs</a> <var>uri</var>
- which are nodes of <var>G</var>.</li>
-
- <li>The triple <var>( s, p, o )</var> is in <var>G</var> if and
- only if the triple <var>( M(s), p, M(o) )</var> is in
- <var>G'</var></li>
- </ol>
- <p>With this definition, <var>M</var> shows how each blank node
- in <var>G</var> can be replaced with
- a new blank node to give <var>G'</var>.</p>
-</section>
-
-
-<section id="section-IRIs">
- <h3>IRIs</h3>
-
- <p>An <dfn title="IRI"><acronym title="Internationalized Resource Identifier">IRI</acronym></dfn>
- (Internationalized Resource Identifier) within an RDF graph
- is a Unicode string [[!UNICODE]] that conforms to the syntax
- defined in RFC 3987 [[!IRI]]. IRIs are a generalization of
- <dfn title="URI"><acronym title="Uniform Resource Identifier">URI</acronym>s</dfn>
- [[URI]]. Every absolute URI and URL is an IRI.</p>
-
- <p>IRIs in the RDF abstract syntax MUST be absolute, and MAY
- contain a fragment identifier.</p>
-
- <p>Two IRIs are equal if and only if they are equivalent
- under Simple String Comparison according to
- <a href="http://tools.ietf.org/html/rfc3987#section-5.1">section 5.1</a>
- of [[!IRI]]. Further normalization MUST NOT be performed when
- comparing IRIs for equality.</p>
-
- <p class="note">When IRIs are used in operations that are only
- defined for URIs, they must first be converted according to
- the mapping defined in
- <a href="http://tools.ietf.org/html/rfc3987#section-3.1">section 3.1</a>
- of [[!IRI]]. A notable example is retrieval over the HTTP
- protocol. The mapping involves UTF-8 encoding of non-ASCII
- characters, %-encoding of octets not allowed in URIs, and
- Punycode-encoding of domain names.</p>
-
- <p class="note">Some concrete syntaxes permit relative IRIs
- as a shorthand for absolute IRIs, and define how to resolve
- the relative IRIs against a base IRI.</p>
-
- <p class="note">Previous versions of RDF used the term
- “<dfn>RDF URI Reference</dfn>” instead of “IRI” and allowed
- additional characters:
- “<code><</code>”, “<code>></code>”,
- “<code>{</code>”, “<code>}</code>”,
- “<code>|</code>”, “<code>\</code>”,
- “<code>^</code>”, “<code>`</code>”,
- ‘<code>“</code>’ (double quote), and “<code> </code>” (space).
- In IRIs, these characters must be percent-encoded as
- described in <a href="http://tools.ietf.org/html/rfc3986#section-2.1">section 2.1</a>
- of [[URI]].</p>
-
- <div class="note">
- <p>Interoperability problems can be avoided by minting
- only IRIs that are normalized according to
- <a href="http://tools.ietf.org/html/rfc3987#section-5">Section 5</a>
- of [[!IRI]]. Non-normalized forms that should be avoided
- include:</p>
-
- <ul>
- <li>Uppercase characters in scheme names and domain names</li>
- <li>Percent-encoding of characters where it is not
- required by IRI syntax</li>
- <li>Explicitly stated HTTP default port
- (<code>http://example.com:80/</code>);
- <code>http://example.com/</code> is preferrable</li>
- <li>Completely empty path in HTTP IRIs
- (<code>http://example.com</code>);
- <code>http://example.com/</code> is preferrable</li>
- <li>“<code>/./</code>” or “<code>/../</code>” in the path
- component of an IRI</li>
- <li>Lowercase hexadecimal letters within percent-encoding
- triplets (“<code>%3F</code>” is preferable over
- “<code>%3f</code>”)</li>
- <li>Punycode-encoding of Internationalized Domain Names
- in IRIs</li>
- <li>IRIs that are not in Unicode Normalization
- Form C [[!NFC]]</li>
- </ul>
- </div>
-</section>
-
-
-<section id="section-Graph-Literal">
- <h3>RDF Literals</h3>
-
- <p class="issue">Currently, there are three different
- kinds of literals for expressing strings: plain literals,
- <a href=""><code>rdf:PlainLiteral</code></a> [[RDF-PLAINLITERAL]],
- and <code>xsd:string</code>. Some consolidation of these
- forms is under consideration. This is
- <a href="http://www.w3.org/2011/rdf-wg/track/issues/12">ISSUE-12</a>.</p>
-
-<p>A <dfn>literal</dfn> in an <a>RDF graph</a>
-contains one or two named components.</p>
-<p>All literals have a <dfn>lexical form</dfn> being a Unicode
-[[!UNICODE]] string, which SHOULD be in Normal Form C [[!NFC]].</p>
-
-
- <p><dfn title="plain literal">Plain literals</dfn> have
- a <a>lexical form</a> and optionally a <dfn>language tag</dfn> as
- defined by [[!BCP47]]. The language tag, if present, MUST be
- well-formed according to
- <a href="http://tools.ietf.org/html/rfc5646#section-2.2.9">section 2.2.9</a>
- of [[!BCP47]], and MUST be normalized to lowercase.</p>
-
- <p><dfn title="typed literal">Typed literals</dfn> have a <a>lexical form</a>
- and a <dfn>datatype IRI</dfn> being an <a>IRI</a>.</p>
-
-
- <p class="note">Literals in which the lexical form begins with a
- composing character (as defined by [[CHARMOD]]) are allowed however they may cause
- interoperability problems, particularly with XML version 1.1 [[XML11]].</p>
-
- <p class="note">Earlier versions of RDF permitted tags that
- adhered to the generic tag/subtag syntax of language tags,
- but were not well-formed according to [[!BCP47]]. Such
- language tags do not conform to RDF 1.1.</p>
-
- <p class="note">When using the language tag, care must be
- taken not to confuse language with locale. The language
- tag relates only to human language text. Presentational
- issues should
- be addressed in end-user applications.</p>
-
- <p class="note">The case normalization of
-language tags is part of
- the description of the abstract syntax, and consequently the abstract
- behaviour of RDF applications. It does not constrain an
- RDF implementation to actually normalize the case. Crucially, the result
- of comparing two language tags should not be sensitive to the case of
- the original input.</p>
-
-
-<section id="section-Literal-Equality">
- <h4>Literal Equality</h4>
-
- <p>Two literals are equal if and only if all of the following
- hold:</p>
-
- <ul>
- <li>The strings of the two lexical forms compare equal, character
- by character.</li>
-
- <li>Either both or neither have language tags.</li>
-
- <li>The language tags, if any, compare
- equal.</li>
-
- <li>Either both or neither have datatype IRIs.</li>
-
- <li>The two datatype IRIs, if any, compare equal, character by
- character.</li>
- </ul>
-
- <p class="note">RDF Literals are distinct and distinguishable
- from <a title="IRI">IRIs</a>; e.g. <code>http://example.org/</code> as an RDF
- Literal (untyped, without a language tag) is not equal to
- <code>http://example.org/</code> as an IRI.</p>
-</section>
-
-
-<section id="section-Literal-Value">
- <h4>The Value Corresponding to a Typed Literal</h4>
-
- <p>The datatype IRI refers to a <a href=
- "#section-Datatypes">datatype</a>. For XML Schema <a href=
- "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#built-in-datatypes">
- built-in</a> datatypes, IRIs such as
- <code>http://www.w3.org/2001/XMLSchema#int</code> are used. The IRI
- of the datatype <a href="#section-XMLLiteral"><tt>rdf:XMLLiteral</tt></a> may be used.
- There may be other, implementation dependent, mechanisms by which
- IRIs refer to datatypes.</p>
-
- <p>The <em>value</em> associated with a typed literal is found by
- applying the lexical-to-value mapping associated with the datatype IRI to
- the lexical form.
- </p>
-
- <p>
- If the lexical form is not in
- the lexical space of the datatype associated with the datatype IRI,
-then no literal value can be associated with the typed literal.
-Such a case, while in error, is not <em>syntactically</em> ill-formed.</p>
-<!--
- <p>A typed literal for which the datatype does not map the lexical
- form to a value is not syntactically ill-formed.</p>
--->
-
-
- <p class="note">
-In application contexts, comparing the values of typed literals (see
-<a href="#section-Literal-Value">
-section
-6.5.2</a>)
-is usually more helpful than comparing their syntactic forms (see
-<a href="#section-Literal-Equality">
-section
-6.5.1</a>).
-Similarly, for comparing RDF Graphs,
-semantic notions of entailment (see
-[[!RDF-MT]]) are usually
-more helpful than syntactic equality (see
-<a href="#section-graph-equality">
-section
-6.3</a>).</p>
-
-</section>
-
-</section>
-
-
-<section id="section-blank-nodes">
- <h3>Blank Nodes</h3>
-
-<p>
-The <dfn title="blank node">blank nodes</dfn> in an RDF graph
-are drawn from an infinite set.
-This set of blank nodes, the set of all <a title="IRI">IRIs</a>
-and the set of all <a title="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>
-
-
-<section id="section-skolemization">
- <h4>Replacing Blank Nodes with IRIs</h4>
-
- <p>Blank nodes do not have identifiers in the RDF abstract syntax. The
- <a title="blank node identifier">blank node identifiers</a> introduced
- by some concrete syntaxes have only
- local scope and are purely an artifact of the serialization.</p>
-
- <p>In situations where stronger identification is needed, systems MAY
- systematically transform some or all of the blank nodes in an RDF graph
- into IRIs [[!IRI]]. Systems wishing to do this SHOULD mint a new, globally
- unique IRI (a <dfn>Skolem IRI</dfn>) for each blank node so transformed.</p>
-
- <p>This transformation does not change the meaning of an RDF graph,
- provided that the Skolem IRIs do not occur anywhere else.</p>
-
- <p>Systems may wish to mint Skolem IRIs in such a way that they can
- recognize the IRIs as having been introduced solely to replace a blank
- node, and map back to the source blank node where possible.</p>
-
- <p>Systems that want Skolem IRIs to be recognizable outside of the system
- boundaries SHOULD use a well-known IRI [[WELL-KNOWN]] with the registered
- name <code>genid</code>. This is an IRI that uses the HTTP or HTTPS scheme,
- or another scheme that has been specified to use well-known IRIs; and whose
- path component starts with <code>/.well-known/genid/</code>.
-
- <p>For example, the authority responsible for the domain
- <code>example.com</code> could mint the following recognizable Skolem IRI:</p>
-
- <pre>http://example.com/.well-known/genid/d26a2d0e98334696f4ad70a677abc1f6</pre>
-
- <p class="issue">IETF registration of the <code>genid</code> name is
- currently in progress.</p>
-
- <p class="note">RFC 5785 [[WELL-KNOWN]] only specifies well-known URIs,
- not IRIs. For the purpose of this document, a well-known IRI is any
- IRI that results in a well-known URI after IRI-to-URI mapping [[!IRI]].</p>
-</section>
-
-</section>
-
-
-<section id="section-multigraph">
- <h2>Abstract Syntax for Working with Multiple Graphs</h2>
-
- <div class="issue">
- <p>The Working Group will standardize a model and semantics for
- multiple graphs and graphs stores. The
- <a href="http://www.w3.org/2011/01/rdf-wg-charter">charter</a> notes:</p>
-
- <blockquote>The RDF Community has used the
- term “named graphs” for a number of years in various settings,
- but this term is ambiguous, and often refers to what could rather
- be referred as quoted graphs, graph literals, IRIs for graphs,
- knowledge bases, graph stores, etc. The term “Support for Multiple
- Graphs and Graph Stores” is used as a neutral term in this charter;
- this term is not and should not be considered as definitive.
- The Working Group will have to define the right term(s).</blockquote>
-
- <p>Progress on the design for this feature is tracked under multiple
- issues:</p>
-
- <ul>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/5">ISSUE-5: Should we define Graph Literal datatypes?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/14">ISSUE-14: What is a named graph and what should we call it?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/15">ISSUE-15: What is the relationship between the IRI and the triples in a dataset/quad-syntax/etc</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/17">ISSUE-17: How are RDF datasets to be merged?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/22">ISSUE-22: Does multigraph syntax need to support empty graphs?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/28">ISSUE-28: Do we need syntactic nesting of graphs (g-texts) as in N3?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/29">ISSUE-29: Do we support SPARQL's notion of "default graph"?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/30">ISSUE-30: How does SPARQL's notion of RDF dataset relate our notion of multiple graphs?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/32">ISSUE-32: Can we identify both g-boxes and g-snaps?</a></li>
- <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/33">ISSUE-33: Do we provide a way to refer to sub-graphs and/or individual triples?</a></li>
- </ul>
- </div>
-</section>
-
-</section>
-
-
-<section id="section-fragID" class="informative">
- <h2>Fragment Identifiers</h2>
-
- <p class="issue">This section does not address the case where RDF is
- embedded in other document formats, such as in RDFa or when an RDF/XML
- fragment is embedded in SVG. It has been suggested that this may be
- a general issue for the TAG about the treatment of
- fragment identifiers when one language is embedded in another. This is
- <a href="http://www.w3.org/2011/rdf-wg/track/issues/37">ISSUE-37</a>.</p>
-
- <p class="issue">This section requires updates to address the
- change from <a title="RDF URI Reference">URI References</a> to <a title="IRI">IRIs</a>.</p>
-
- <p>RDF uses an <a title="RDF URI Reference">RDF URI
- Reference</a>, which may include a fragment identifier, as a
- context free identifier for a resource. RFC 2396 states that the meaning of a fragment
- identifier depends on the MIME content-type of a document, i.e.
- is context dependent.</p>
- <p>These apparently conflicting views are reconciled by
- considering that a URI reference in an RDF graph is treated
- with respect to the MIME type <code>application/rdf+xml</code>
- [[!RDF-MIME-TYPE]]. 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 <code>application/rdf+xml</code> 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 <code>eg:someurl#frag</code> is used in an RDF
- document, <code>eg:someurl</code> is taken to
- designate some RDF document (even when no such document can
- be retrieved).</li>
- <li><code>eg:someurl#frag</code> means the thing
- that is indicated, according to the rules of the
- <code>application/rdf+xml</code> MIME content-type as
- a “fragment” or “view” of the RDF document at
- <code>eg:someurl</code>. If the document does not
- exist, or cannot be retrieved, or is available only in
- formats other than <code>application/rdf+xml</code>, then exactly what
- that view may be is somewhat undetermined, but that does not
- prevent use of RDF to say things about it.</li>
- <li>the RDF treatment of a fragment identifier allows it to
- indicate a thing that is entirely external to the document,
- or even to the “shared information space” known as the Web.
- That is, it can be a more general idea, like some particular
- car or a mythical Unicorn.</li>
- <li>in this way, an <code>application/rdf+xml</code> document acts as an
- intermediary between some Web retrievable documents (itself,
- at least, also any other Web retrievable 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>
-</section>
-
-
-<section id="section-Acknowledgments" class="informative">
- <h2>Acknowledgments</h2>
-
- <p class="issue">This section does not yet list those who made
- contributions to the RDF 1.1 version, nor does it list the
- current RDF WG members.</p>
-
- <p>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>
-</section>
-
-
-<section class="appendix informative" id="changes">
- <h2>Changes from RDF 2004</h2>
-
- <ul>
- <li>2011-06-01: Replaced the URI References section with <a href="#section-IRIs">new section on IRIs</a>, and changed “RDF URI Reference” to “IRI” throughout the document, except in <a href="#section-fragID">section 8</a>.</li>
- <li>2011-06-01: Changed language tag definition to require well-formedness according to BCP47; added a note that this invalidates some RDF</li>
- <li>2011-05-25: Added boxes for known WG issues throught the document</li>
- <li>2011-05-25: Deleted “Structure of this Document” section, it added no value beyond the TOC</li>
- <li>2011-05-25: Implemented resolution of <a href="http://www.w3.org/2011/rdf-wg/track/issues/40">ISSUE-40: Skolemization advice in the RDF dcocument</a> by adding a section on <a href="#section-skolemization">Replacing Blank Nodes with IRIs</a></li>
- <li>2011-05-25: rdf:XMLLiteral is disjoint from any datatype not explicitly related to it, per erratum <a href="http://www.w3.org/2001/sw/RDFCore/errata#concept-xmlliteral">[concept-xmlliteral]</a></li>
- <li>2011-05-25: Added Conformance section with RFC2119 reference</li>
- <li>2011-05-25: Updated all W3C references to latest editions, and Unicode from v3 to v4</li>
- <li>2011-05-24: Converted to ReSpec, changed metadata to reflect RDF 1.1</li>
- </ul>
-</section>
-
-
-<section id="references">
- <div class="issue">
- <ul>
- <li>RFC 2279 is obsoleted by RFC 3629</li>
- <li>Change OWL reference to OWL2?</li>
- <li>Change XHTML10 reference to XHTML5?</li>
- </ul>
- </div>
-</section>
-
- </body>
-</html>
-
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+++ b/rdf-concepts/index.html Wed Jun 01 19:12:07 2011 +0100
@@ -0,0 +1,1563 @@
+<!DOCTYPE html>
+<html lang="en">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+ <title>RDF 1.1 Concepts and Abstract Syntax</title>
+ <style>
+.figure { font-weight: bold; text-align: center; }
+ </style>
+ <script src='../ReSpec.js/js/respec.js' class='remove'></script>
+ <script class='remove'>
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+ // specification status (e.g. WD, LCWD, NOTE, etc.). If in doubt use ED.
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+
+ // the specification's short name, as in http://www.w3.org/TR/short-name/
+ shortName: "rdf11-concepts",
+
+ // if your specification has a subtitle that goes below the main
+ // formal title, define it here
+ // subtitle : "an excellent document",
+
+ // if you wish the publication date to be other than today, set this
+ // publishDate: "2009-08-06",
+
+ // if the specification's copyright date is a range of years, specify
+ // the start date here:
+ copyrightStart: "2004",
+
+ // if there is a previously published draft, uncomment this and set its YYYY-MM-DD date
+ // and its maturity status
+// previousPublishDate: "2004-02-10",
+// previousMaturity: "REC",
+
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+//@@@
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+
+ // if this is a LCWD, uncomment and set the end of its review period
+ // lcEnd: "2009-08-05",
+
+ // if there is an earler version of this specification at the Recommendation level,
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+ // necessary.
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+
+ // if you want to have extra CSS, append them to this list
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+
+ // editors, add as many as you like
+ // only "name" is required
+ editors: [
+ { name: "Richard Cyganiak", url: "http://richard.cyganiak.de/",
+ company: "DERI, NUI Galway", companyURL: "http://www.deri.ie/",
+ },
+// @@@ Details for David?
+ { name: "David Wood", // url: "http://example.org/",
+ company: "Talis", companyURL: "http://www.talis.com/",
+ },
+ ],
+ otherContributors: {
+ "Previous editor": [
+// @@@ Graham's affiliation has changed
+ { name: "Graham Klyne",
+ url: "http://www.ninebynine.org/",
+ company: "Nine by Nine",
+ //companyURL: "http://example.com/"
+ //mailto: "GK@NineByNine.org",
+ },
+// @@@ Jeremy's affiliation has changed
+ { name: "Jeremy J. Carroll",
+ //url: "http://www-uk.hpl.hp.com/people/jjc/",
+ company: "Hewlett Packard Labs",
+ //companyURL: "http://example.com/"
+ //mailto: "jjc@hpl.hp.com",
+ },
+// @@@ Brian's affiliation has changed
+ { name: "Brian McBride",
+ //url: "http://www-uk.hpl.hp.com/people/bwm/",
+ company: "Hewlett Packard Labs",
+ //companyURL: "http://example.com/"
+ //mailto: "bwm@hplb.hpl.hp.com",
+ note: "RDF 2004 Series Editor",
+ },
+ ],
+ },
+
+ // authors, add as many as you like.
+ // This is optional, uncomment if you have authors as well as editors.
+ // only "name" is required. Same format as editors.
+
+ //authors: [
+ // { name: "Your Name", url: "http://example.org/",
+ // company: "Your Company", companyURL: "http://example.com/" },
+ //],
+
+ // name of the WG
+ wg: "RDF Working Group",
+
+ // URI of the public WG page
+ wgURI: "http://www.w3.org/2011/rdf-wg/",
+
+ // name (with the @w3c.org) of the public mailing to which comments are due
+ wgPublicList: "public-rdf-comments",
+
+ // URI of the patent status for this WG, for Rec-track documents
+ // !!!! IMPORTANT !!!!
+ // This is important for Rec-track documents, do not copy a patent URI from a random
+ // document unless you know what you're doing. If in doubt ask your friendly neighbourhood
+ // Team Contact.
+ wgPatentURI: "http://www.w3.org/2004/01/pp-impl/46168/status",
+
+ // if this parameter is set to true, ReSpec.js will embed various RDFa attributes
+ // throughout the generated specification. The triples generated use vocabulary items
+ // from the dcterms, foaf, and bibo. The parameter defaults to false.
+ doRDFa: true,
+ };
+
+// @@@ A number of references have been patched into the local berjon.biblio and need to be added to the global biblio in CVS:
+ </script>
+ </head>
+
+ <body>
+
+<section id="abstract">
+ <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 IRIs.</p>
+</section>
+
+
+<section id="section-Introduction">
+ <h2>Introduction</h2>
+
+ <p class="issue">This document reflects current progress of the RDF Working
+ Group towards updating the
+ <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">2004
+ version of <em>RDF Concepts and Abstract Syntax</em></a>. The
+ editors expect to work on a number of issues, some of which are
+ listed in boxes like this throughout the document.</p>
+
+ <p>The Resource Description Framework (RDF) is a framework for
+ representing information in the Web.</p>
+
+ <p>This document defines an abstract syntax 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
+ [[XML-INFOSET]]. It also includes discussion of design goals,
+ key concepts, datatyping, character normalization
+ and handling of IRIs.</p>
+
+ <p>Normative documentation of RDF falls into the following
+ areas:</p>
+
+ <ul>
+ <li>XML serialization syntax [[!RDF-SYNTAX-GRAMMAR]],</li>
+
+ <li>formal semantics [[!RDF-MT]], and</li>
+
+ <li>this document (sections 4, 5, 6 and 7).</li>
+ </ul>
+
+ <p class="issue">This document was written when RDF/XML was the
+ only normative syntax. Now it is just one of many syntaxes and
+ it should be de-emphasized accordingly. There is no reason why
+ it should be a normative reference in this document.</p>
+
+ <p>The framework is designed so that vocabularies can be layered.
+The RDF and RDF vocabulary definition (RDF schema)
+languages
+ [[RDF-SCHEMA]] are the first
+ such vocabularies.
+
+ Others (cf. OWL [[OWL-REF]] and
+ the applications mentioned in the primer
+ [[RDF-PRIMER]]) are in development.</p>
+</section>
+
+
+<section id="conformance"></section>
+
+
+<section id="section-Overview" class="informative">
+ <h2>Motivations and Goals</h2>
+
+ <p class="issue">Does this section add value?</p>
+
+ <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>
+
+<section id="section-motivation">
+ <h3>Motivation</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>
+</section>
+
+
+<section>
+ <h3 id="section-design-goals">Design Goals</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 IRI-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>
+
+
+<section id="section-simple-data-model">
+ <h4>A Simple Data Model</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">The term “model” used here in “data model” has a
+ completely different sense to its use in the term “model theory”.
+ See [[!RDF-MT]]
+ for more information about “model theory” as used in the literature of mathematics and logic.</p>
+</section>
+
+
+<section id="section-formal-semantics">
+ <h4>Formal Semantics and Inference</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>
+</section>
+
+
+<section id="section-extensible-vocab">
+ <h4>Extensible IRI-based Vocabulary</h4>
+
+ <p>The vocabulary is fully extensible, being based on IRIs.
+ IRIs 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>
+</section>
+
+
+<section id="section-xml-serialization">
+ <h4>XML-based Syntax</h4>
+
+ <p>RDF has a recommended XML serialization form [[!RDF-SYNTAX-GRAMMAR]], which can be used to encode the
+ data model for exchange of information among applications.</p>
+</section>
+
+
+<section id="section-use-xsd">
+ <h4>Use XML Schema Datatypes</h4>
+
+ <p>RDF can use values represented according to XML schema datatypes
+ [[!XMLSCHEMA-2]], thus assisting the
+ exchange of information between RDF and other XML applications.</p>
+</section>
+
+
+<section id="section-anyone">
+ <h4>Anyone Can Make Statements About Any Resource</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>
+</section>
+
+</section>
+
+</section>
+
+
+<section id="section-Concepts" class="informative">
+ <h2>RDF Concepts</h2>
+
+ <p class="issue">This section is quite redundant with later normative sections and the RDF Primer.</p>
+
+ <p>RDF uses the following key concepts:</p>
+
+ <ul>
+ <li>Graph data model</li>
+
+ <li>IRI-based vocabulary</li>
+
+ <li>Datatypes</li>
+
+ <li>Literals</li>
+
+ <li>XML serialization syntax</li>
+
+ <li>Expression of simple facts</li>
+
+ <li>Entailment</li>
+ </ul>
+
+
+<section id="section-data-model">
+ <h3>Graph Data Model</h3>
+
+ <p>The underlying structure of any expression in RDF is a
+ collection of triples, each consisting of a subject, a
+ predicate and an object. A set of such triples is called an RDF
+ graph (defined more formally in
+<a href="#section-Graph-syntax">section 6</a>). This can be
+ illustrated by a node and directed-arc diagram, in which each
+ triple is represented as a node-arc-node link (hence the term
+ “graph”).</p>
+
+ <div class="figure">
+ <img src="Graph-ex.gif" alt="image of the RDF triple comprising (subject, predicate, object)" />
+ </div>
+
+ <p>Each triple represents a statement of a relationship between
+ the things denoted by the nodes that it links. Each triple has
+ three parts:</p>
+ <ol>
+ <li>a <a>subject</a>,</li>
+ <li>an <a>object</a>, and</li>
+ <li>a <a>predicate</a> (also called a
+ <a>property</a>) that denotes a
+ relationship.</li>
+ </ol>
+ <p>The direction of the arc is significant: it always points
+ toward the object.</p>
+ <p>The <a title="node">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 [[!RDF-MT]].</p>
+</section>
+
+
+<section id="section-IRI-Vocabulary">
+ <h3>IRI-based Vocabulary and Node Identification</h3>
+
+ <p>A <a>node</a> may be an <a>IRI</a>, a <a>literal</a>,
+ or <a title="blank node">blank</a> (having no separate form of identification).
+ Properties are <a title="IRI">IRIs</a>.</p>
+ <p>An <a>IRI</a> or <a>literal</a> used as a node identifies what
+ that node represents. An IRI used as a predicate
+ identifies a relationship between the things represented by the nodes it connects. A
+ predicate IRI may also be a node in the graph.</p>
+ <p>A <a>blank node</a> is a node that is
+ not an IRI or a literal. In the RDF abstract syntax, a
+ blank node is just a unique node that can be used in one or
+ more RDF statements.</p>
+ <p>A convention used by some linear representations of an RDF
+ graph to allow several statements to use the same
+ blank node is to use a <dfn>blank node
+ identifier</dfn>, which is a local identifier that can be
+ distinguished from all IRIs and literals. When graphs are
+ merged, their blank nodes must be kept distinct if meaning is
+ to be preserved; this may call for re-allocation of blank node
+ identifiers. Note that such blank node identifiers are not part
+ of the RDF abstract syntax, and the representation of triples
+ containing blank nodes is entirely dependent on the particular
+ concrete syntax used.</p>
+</section>
+
+
+<section name="section-Datatypes-intro">
+ <h3>Datatypes</h3>
+
+ <p>Datatypes are used by RDF in the representation of values such
+ as integers, floating point numbers and dates.</p>
+
+ <p>
+A datatype consists of a lexical space, a value space and a lexical-to-value
+mapping, see <a href="#section-Datatypes">section 5</a>.
+</p>
+
+ <p>For example, the lexical-to-value mapping for the XML Schema datatype
+ <var>xsd:boolean</var>, where each member of the value space
+ (represented here as 'T' and 'F') has two lexical representations,
+ is as follows:</p>
+
+ <table border="1" cellpadding="5" summary=
+ "A table detailing the xsd:boolean datatype.">
+ <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>{<"true", T>, <"1", T>, <"0", F>,
+ <"false", F>}</td>
+ </tr>
+ </table>
+
+ <p>RDF predefines just one datatype <code><a>rdf:XMLLiteral</a></code>, used for
+ embedding XML in RDF (see <a href="#section-XMLLiteral">section
+ 5.1</a>).</p>
+
+ <p>There is no built-in concept of numbers or dates or other common
+ values. Rather, RDF defers to datatypes that are defined
+ separately, and identified with <a title="IRI">IRIs</a>.
+ The predefined XML Schema
+ datatypes [[!XMLSCHEMA-2]] are expected
+ to be widely used for this purpose.</p>
+
+
+ <p>RDF provides no mechanism for defining new datatypes. XML Schema
+ Datatypes [[!XMLSCHEMA-2]] provides an
+ extensibility framework suitable for defining new datatypes for use
+ in RDF.</p>
+</section>
+
+
+<section name="section-Literals">
+ <h3> Literals</h3>
+
+ <p><a title="literal">Literals</a> are used to identify values such as numbers and dates
+ by means of a lexical representation. Anything represented by a
+ literal could also be represented by an <a>IRI</a>, but it is often more
+ convenient or intuitive to use literals.</p>
+
+ <p>A literal may be the object of an RDF statement, but not the
+ subject or the predicate.</p>
+
+ <p>Literals may be <cite>plain</cite> or <cite>typed</cite> :</p>
+
+ <ul>
+ <li>A <a>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 [[!RDF-MT]], these plain literals are
+ self-denoting.</li>
+
+
+
+ <li>A <a>typed literal</a> is a string combined with a
+ <a>datatype IRI</a>. It denotes the
+ member of the identified datatype's value space obtained by
+ applying the lexical-to-value mapping to the literal string.</li>
+ </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"><xsd:boolean, "true"></td>
+
+ <td align="center"><"true", T></td>
+
+ <td align="center">T</td>
+ </tr>
+
+ <tr>
+ <td align="center"><xsd:boolean, "1"></td>
+
+ <td align="center"><"1", T></td>
+
+ <td align="center">T</td>
+ </tr>
+
+ <tr>
+ <td align="center"><xsd:boolean, "false"></td>
+
+ <td align="center"><"false", F></td>
+
+ <td align="center">F</td>
+ </tr>
+
+ <tr>
+ <td align="center"><xsd:boolean, "0"></td>
+
+ <td align="center"><"0", F></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.
+[[XHTML10]] 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 [[!NFC]]. This is motivated
+by [[CHARMOD]] particularly
+<a href="http://www.w3.org/TR/2003/WD-charmod-20030822/#sec-Normalization">section 4
+Early Uniform Normalization</a>.
+</p>
+
+</section>
+
+
+<section id="section-SimpleFacts">
+ <h3>RDF Expression of Simple Facts</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 <code>rdf:type</code> property whose value corresponds
+to the table name.
+</p>
+
+ <p>As an example, consider Figure 6 from the [[RDF-PRIMER]]:
+
+</p>
+
+ <div class="figure">
+ <img src="fig6may19" alt="Using a Blank Node" /><br />
+ RDF Primer Figure 6: Using a Blank Node
+ </div>
+
+
+ <p>
+This information might correspond to a row in a table <code>"STAFFADDRESSES"</code>,
+ with a primary key
+<code>STAFFID</code>,
+ and additional columns
+<code>STREET</code>,
+<code>STATE</code>,
+<code>CITY</code> and
+<code>POSTALCODE</code>.
+ </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 IRI-based vocabularies, RDF
+ provides for expression of facts about arbitrary subjects; i.e.
+ assertions of named properties about specific named things. An IRI
+ 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 [[TAP-RBD]].
+ -->
+ </p>
+</section>
+
+
+<section id="section-Entailment">
+ <h3>Entailment</h3>
+
+ <p>The ideas on meaning and inference in RDF are underpinned by the
+ formal concept of <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#entail">
+<cite>entailment</cite></a>, as
+ discussed in the RDF
+ semantics document [[!RDF-MT]].
+In brief, an RDF expression A is said to
+<dfn title="entailment">entail</dfn> another RDF 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>
+</section>
+
+</section>
+
+
+<section id="section-URIspaces">
+ <h2>RDF Vocabulary IRI and Namespace</h2>
+
+ <p>RDF uses <a title="IRI">IRIs</a> to identify resources
+ and properties. Certain
+ IRIs are given specific meaning by RDF. Specifically, IRIs
+ with the following leading substring are defined by the RDF
+ specifications:</p>
+
+ <ul>
+ <li><code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>
+ (conventionally associated with namespace prefix <code>rdf:</code>)</li>
+<!--
+ <li><code>http://www.w3.org/2000/01/rdf-schema#</code>
+ (conventionally associated with namespace prefix <code>rdfs:</code>)</li>
+-->
+ </ul>
+ <p>Used with the RDF/XML serialization, this IRI prefix
+ string corresponds to XML namespace names [[!XML-NAMES]] associated with the RDF
+ vocabulary terms.</p>
+
+ <p class="note">This namespace name is the same
+ as that used in the earlier RDF recommendation [[RDF-SYNTAX]].</p>
+
+ <p>Vocabulary terms in the <code>rdf:</code>
+ 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 [[!RDF-SYNTAX-GRAMMAR]]. 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 <code>rdfs:</code> namespace are defined in the RDF
+ schema vocabulary specification [[RDF-SCHEMA]].</p>
+-->
+</section>
+
+
+<section name="section-Datatypes">
+ <h2>Datatypes</h2>
+
+ <p class="issue">This section perhaps should discuss
+ <a href="http://www.w3.org/TR/rdf-mt/#dtype_interp">the XSD datatype map</a>
+ and <code><a href="http://www.w3.org/TR/rdf-plain-literal/">rdf:PlainLiteral</a></code>.</p>
+
+<p>
+The datatype abstraction used in RDF is compatible with
+the abstraction used in
+XML Schema Part 2:
+ Datatypes [[!XMLSCHEMA-2]].</p>
+<p>
+A datatype consists of a lexical space, a value space and a lexical-to-value
+mapping.
+</p>
+<p>The <dfn>lexical space</dfn> of a datatype is a set of Unicode [[!UNICODE]] strings.</p>
+<p>
+The <dfn>lexical-to-value mapping</dfn> of a datatype is a set of pairs whose
+first element belongs to
+the <a>lexical space</a> of the datatype,
+and the second element belongs to the
+ <dfn>value space</dfn> of the datatype:
+</p>
+<ul>
+<li>
+Each member of the lexical space is paired with (maps to) exactly one member
+of the value space.
+</li>
+<li>
+Each member of the value space may be paired with any number (including
+zero) of members of the lexical space (lexical representations for that
+value).
+</li>
+</ul>
+<p>
+A datatype is identified by one or more IRIs.
+</p>
+<p>
+RDF may be used with any datatype definition that conforms to this
+abstraction, even if not defined in terms of XML Schema.
+</p>
+ <p>Certain XML Schema built-in datatypes are not suitable for use
+ within RDF. For example, the
+<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#QName">QName</a>
+datatype requires a namespace declaration to be in scope during
+ the mapping, and is not recommended for use in RDF.
+ [[!RDF-MT]] contains a
+<a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#dtype_interp">more detailed discussion</a>
+ of specific XML Schema built-in datatypes. </p>
+
+<div class="note">
+<p>When the datatype is defined using XML Schema:
+</p>
+<ul>
+<li>
+All values correspond to some lexical form, either using
+the lexical-to-value mapping of the datatype or if it is a union
+datatype with a lexical mapping associated with one of the member
+datatypes.
+</li>
+<li>
+XML Schema facets remain part of the datatype and are used by the XML
+Schema mechanisms that control the lexical space and the value space;
+however, RDF does not define a standard mechanism to access these facets.</li>
+
+<li>In [[XMLSCHEMA-1]],
+<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>
+
+
+<section id="section-XMLLiteral">
+ <h3>XML Content within an RDF Graph</h3>
+
+ <p class="issue">The canonicalization rules required for XML literals
+ are quite complicated. Increasingly, RDF is produced and consumed in
+ environments where no XML parser and canonicalization engine is
+ available. A possible change to relax the requirements for the
+ lexical space, while retaining the value space, is under discussion.
+ This is <a href="http://www.w3.org/2011/rdf-wg/track/issues/13">ISSUE-13</a>.</p>
+
+ <p>RDF provides for XML content as a possible literal value. This
+ typically originates from the use of
+ <code>rdf:parseType="Literal"</code> in the RDF/XML Syntax [[!RDF-SYNTAX-GRAMMAR]].</p>
+
+ <p>Such content is indicated in an RDF graph using a typed literal
+ whose datatype is a special built-in datatype
+ <dfn>rdf:XMLLiteral</dfn>,
+ defined as follows.</p>
+
+
+ <dl>
+ <dt><a name="XMLLiteral-uri" id="XMLLiteral-uri">An IRI for
+identifying this datatype</a></dt>
+
+ <dd>is
+ <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral</code>.</dd>
+
+
+
+
+ <dt><a name="XMLLiteral-lexical-space" id="XMLLiteral-lexical-space">The lexical space</a></dt>
+
+<dd>is the set of all
+strings:
+<ul>
+<li>which are well-balanced, self-contained
+<a href="http://www.w3.org/TR/2000/REC-xml-20001006#NT-content">
+XML content</a>
+[[!XML10]];
+</li>
+<li>for which encoding as UTF-8
+[[!RFC2279]] 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>) [[!XML-EXC-C14N]];
+</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> [[!XML-NAMES]]</li>
+</ul>
+</dd>
+
+
+ <dt><a name="XMLLiteral-value-space" id="XMLLiteral-value-space">The value space</a></dt>
+
+ <dd>is a set of entities, called XML values, which is:
+<ul>
+<li>disjoint from the lexical space;</li>
+<li>disjoint from the value space of any other datatype that is not explicitly defined as a sub- or supertype of this datatype;</li>
+<li>disjoint from the set of Unicode character strings [[!UNICODE]];</li>
+<li>and in 1:1 correspondence with the lexical space.</li>
+</ul>
+</dd>
+
+ <dt><a name="XMLLiteral-mapping" id="XMLLiteral-mapping">The lexical-to-value mapping</a></dt>
+
+ <dd>
+is a one-one mapping from the lexical space onto the value space,
+ i.e. it is both injective and surjective.
+</dd>
+
+
+
+ </dl>
+
+
+ <p class="note">Not all values of this datatype are compliant
+ with XML 1.1 [[XML11]]. If compliance
+ with XML 1.1 is desired, then only those values that are
+<a href="http://www.w3.org/TR/2002/CR-xml11-20021015/#sec2.13">fully
+ normalized</a> according to XML 1.1 should be used.</p>
+
+ <p class="note">XML values can be thought of as the
+[[XML-INFOSET]] or the [[XPATH]]
+nodeset corresponding to the lexical form, with an appropriate equality
+function.</p>
+
+ <p class="note">RDF applications may use additional equivalence relations, such as
+that which relates an
+<a href="http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#string"><code>xsd:string</code></a>
+
+with an <code>rdf:XMLLiteral</code> corresponding to
+a single text node of the same string.</p>
+
+</section>
+
+</section>
+
+
+<section id="section-Graph-syntax">
+ <h2>Abstract Syntax</h2>
+
+ <p>This section defines the RDF abstract syntax. The RDF abstract
+ syntax is a set of triples, called the RDF graph.</p>
+
+ <p>This section also defines equivalence between RDF graphs. A
+ definition of equivalence is needed to support the RDF Test Cases
+ [[RDF-TESTCASES]] specification.</p>
+
+<p class="note">This <em>abstract</em> syntax is the
+syntax over which the formal semantics are defined.
+Implementations are free to represent RDF graphs in
+any other equivalent form. As an example:
+in an RDF graph,
+literals with datatype <tt>rdf:XMLLiteral</tt> can be represented
+in a non-canonical
+format, and canonicalization performed during the comparison between two
+such literals. In this example the comparisons may be
+being performed either between syntactic structures or
+between their denotations in the domain of discourse.
+Implementations that do not require any such comparisons can
+hence be optimized.
+</p>
+
+ <p class="issue">The SPARQL WG proposed to add definitions for
+ “RDF Term” and “Simple Literal”.</p>
+
+
+<section id="section-triples">
+ <h3>RDF Triples</h3>
+
+ <p>An <dfn>RDF triple</dfn> contains three components:</p>
+
+ <ul>
+ <li>the <dfn>subject</dfn>, which is an
+ <a>IRI</a> or a <a>blank node</a></li>
+
+ <li>the <dfn>predicate</dfn>, which is an <a>IRI</a></li>
+
+ <li>the <dfn>object</dfn>, which is an <a>IRI</a>,
+ a <a>literal</a> or a <a>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>property</dfn> of the triple.</p>
+</section>
+
+
+<section id="section-rdf-graph">
+ <h3>RDF Graph</h3>
+
+ <p>An <dfn>RDF graph</dfn> is a set of RDF triples.</p>
+
+ <p>The set of <dfn title="node">nodes</dfn> of an RDF graph is the set of subjects and objects of
+ triples in the graph.</p>
+</section>
+
+
+<section id="section-graph-equality">
+ <h3>Graph Equivalence</h3>
+
+ <p>Two <a title="RDF graph">RDF graphs</a> <var>G</var> and <var>G'</var> are equivalent if there
+ is a bijection <var>M</var> between the sets of nodes of the two graphs,
+ such that:</p>
+
+ <ol>
+ <li><var>M</var> maps blank nodes to blank nodes.</li>
+ <li><var>M(lit)=lit</var> for all <a title="literal">RDF literals</a> <var>lit</var> which
+ are nodes of <var>G</var>.</li>
+
+ <li><var>M(uri)=uri</var> for all <a title="IRI">IRIs</a> <var>uri</var>
+ which are nodes of <var>G</var>.</li>
+
+ <li>The triple <var>( s, p, o )</var> is in <var>G</var> if and
+ only if the triple <var>( M(s), p, M(o) )</var> is in
+ <var>G'</var></li>
+ </ol>
+ <p>With this definition, <var>M</var> shows how each blank node
+ in <var>G</var> can be replaced with
+ a new blank node to give <var>G'</var>.</p>
+</section>
+
+
+<section id="section-IRIs">
+ <h3>IRIs</h3>
+
+ <p>An <dfn title="IRI"><acronym title="Internationalized Resource Identifier">IRI</acronym></dfn>
+ (Internationalized Resource Identifier) within an RDF graph
+ is a Unicode string [[!UNICODE]] that conforms to the syntax
+ defined in RFC 3987 [[!IRI]]. IRIs are a generalization of
+ <dfn title="URI"><acronym title="Uniform Resource Identifier">URI</acronym>s</dfn>
+ [[URI]]. Every absolute URI and URL is an IRI.</p>
+
+ <p>IRIs in the RDF abstract syntax MUST be absolute, and MAY
+ contain a fragment identifier.</p>
+
+ <p>Two IRIs are equal if and only if they are equivalent
+ under Simple String Comparison according to
+ <a href="http://tools.ietf.org/html/rfc3987#section-5.1">section 5.1</a>
+ of [[!IRI]]. Further normalization MUST NOT be performed when
+ comparing IRIs for equality.</p>
+
+ <p class="note">When IRIs are used in operations that are only
+ defined for URIs, they must first be converted according to
+ the mapping defined in
+ <a href="http://tools.ietf.org/html/rfc3987#section-3.1">section 3.1</a>
+ of [[!IRI]]. A notable example is retrieval over the HTTP
+ protocol. The mapping involves UTF-8 encoding of non-ASCII
+ characters, %-encoding of octets not allowed in URIs, and
+ Punycode-encoding of domain names.</p>
+
+ <p class="note">Some concrete syntaxes permit relative IRIs
+ as a shorthand for absolute IRIs, and define how to resolve
+ the relative IRIs against a base IRI.</p>
+
+ <p class="note">Previous versions of RDF used the term
+ “<dfn>RDF URI Reference</dfn>” instead of “IRI” and allowed
+ additional characters:
+ “<code><</code>”, “<code>></code>”,
+ “<code>{</code>”, “<code>}</code>”,
+ “<code>|</code>”, “<code>\</code>”,
+ “<code>^</code>”, “<code>`</code>”,
+ ‘<code>“</code>’ (double quote), and “<code> </code>” (space).
+ In IRIs, these characters must be percent-encoded as
+ described in <a href="http://tools.ietf.org/html/rfc3986#section-2.1">section 2.1</a>
+ of [[URI]].</p>
+
+ <div class="note">
+ <p>Interoperability problems can be avoided by minting
+ only IRIs that are normalized according to
+ <a href="http://tools.ietf.org/html/rfc3987#section-5">Section 5</a>
+ of [[!IRI]]. Non-normalized forms that should be avoided
+ include:</p>
+
+ <ul>
+ <li>Uppercase characters in scheme names and domain names</li>
+ <li>Percent-encoding of characters where it is not
+ required by IRI syntax</li>
+ <li>Explicitly stated HTTP default port
+ (<code>http://example.com:80/</code>);
+ <code>http://example.com/</code> is preferrable</li>
+ <li>Completely empty path in HTTP IRIs
+ (<code>http://example.com</code>);
+ <code>http://example.com/</code> is preferrable</li>
+ <li>“<code>/./</code>” or “<code>/../</code>” in the path
+ component of an IRI</li>
+ <li>Lowercase hexadecimal letters within percent-encoding
+ triplets (“<code>%3F</code>” is preferable over
+ “<code>%3f</code>”)</li>
+ <li>Punycode-encoding of Internationalized Domain Names
+ in IRIs</li>
+ <li>IRIs that are not in Unicode Normalization
+ Form C [[!NFC]]</li>
+ </ul>
+ </div>
+</section>
+
+
+<section id="section-Graph-Literal">
+ <h3>RDF Literals</h3>
+
+ <p class="issue">Currently, there are three different
+ kinds of literals for expressing strings: plain literals,
+ <a href=""><code>rdf:PlainLiteral</code></a> [[RDF-PLAINLITERAL]],
+ and <code>xsd:string</code>. Some consolidation of these
+ forms is under consideration. This is
+ <a href="http://www.w3.org/2011/rdf-wg/track/issues/12">ISSUE-12</a>.</p>
+
+<p>A <dfn>literal</dfn> in an <a>RDF graph</a>
+contains one or two named components.</p>
+<p>All literals have a <dfn>lexical form</dfn> being a Unicode
+[[!UNICODE]] string, which SHOULD be in Normal Form C [[!NFC]].</p>
+
+
+ <p><dfn title="plain literal">Plain literals</dfn> have
+ a <a>lexical form</a> and optionally a <dfn>language tag</dfn> as
+ defined by [[!BCP47]]. The language tag, if present, MUST be
+ well-formed according to
+ <a href="http://tools.ietf.org/html/rfc5646#section-2.2.9">section 2.2.9</a>
+ of [[!BCP47]], and MUST be normalized to lowercase.</p>
+
+ <p><dfn title="typed literal">Typed literals</dfn> have a <a>lexical form</a>
+ and a <dfn>datatype IRI</dfn> being an <a>IRI</a>.</p>
+
+
+ <p class="note">Literals in which the lexical form begins with a
+ composing character (as defined by [[CHARMOD]]) are allowed however they may cause
+ interoperability problems, particularly with XML version 1.1 [[XML11]].</p>
+
+ <p class="note">Earlier versions of RDF permitted tags that
+ adhered to the generic tag/subtag syntax of language tags,
+ but were not well-formed according to [[!BCP47]]. Such
+ language tags do not conform to RDF 1.1.</p>
+
+ <p class="note">When using the language tag, care must be
+ taken not to confuse language with locale. The language
+ tag relates only to human language text. Presentational
+ issues should
+ be addressed in end-user applications.</p>
+
+ <p class="note">The case normalization of
+language tags is part of
+ the description of the abstract syntax, and consequently the abstract
+ behaviour of RDF applications. It does not constrain an
+ RDF implementation to actually normalize the case. Crucially, the result
+ of comparing two language tags should not be sensitive to the case of
+ the original input.</p>
+
+
+<section id="section-Literal-Equality">
+ <h4>Literal Equality</h4>
+
+ <p>Two literals are equal if and only if all of the following
+ hold:</p>
+
+ <ul>
+ <li>The strings of the two lexical forms compare equal, character
+ by character.</li>
+
+ <li>Either both or neither have language tags.</li>
+
+ <li>The language tags, if any, compare
+ equal.</li>
+
+ <li>Either both or neither have datatype IRIs.</li>
+
+ <li>The two datatype IRIs, if any, compare equal, character by
+ character.</li>
+ </ul>
+
+ <p class="note">RDF Literals are distinct and distinguishable
+ from <a title="IRI">IRIs</a>; e.g. <code>http://example.org/</code> as an RDF
+ Literal (untyped, without a language tag) is not equal to
+ <code>http://example.org/</code> as an IRI.</p>
+</section>
+
+
+<section id="section-Literal-Value">
+ <h4>The Value Corresponding to a Typed Literal</h4>
+
+ <p>The datatype IRI refers to a <a href=
+ "#section-Datatypes">datatype</a>. For XML Schema <a href=
+ "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#built-in-datatypes">
+ built-in</a> datatypes, IRIs such as
+ <code>http://www.w3.org/2001/XMLSchema#int</code> are used. The IRI
+ of the datatype <a href="#section-XMLLiteral"><tt>rdf:XMLLiteral</tt></a> may be used.
+ There may be other, implementation dependent, mechanisms by which
+ IRIs refer to datatypes.</p>
+
+ <p>The <em>value</em> associated with a typed literal is found by
+ applying the lexical-to-value mapping associated with the datatype IRI to
+ the lexical form.
+ </p>
+
+ <p>
+ If the lexical form is not in
+ the lexical space of the datatype associated with the datatype IRI,
+then no literal value can be associated with the typed literal.
+Such a case, while in error, is not <em>syntactically</em> ill-formed.</p>
+<!--
+ <p>A typed literal for which the datatype does not map the lexical
+ form to a value is not syntactically ill-formed.</p>
+-->
+
+
+ <p class="note">
+In application contexts, comparing the values of typed literals (see
+<a href="#section-Literal-Value">
+section
+6.5.2</a>)
+is usually more helpful than comparing their syntactic forms (see
+<a href="#section-Literal-Equality">
+section
+6.5.1</a>).
+Similarly, for comparing RDF Graphs,
+semantic notions of entailment (see
+[[!RDF-MT]]) are usually
+more helpful than syntactic equality (see
+<a href="#section-graph-equality">
+section
+6.3</a>).</p>
+
+</section>
+
+</section>
+
+
+<section id="section-blank-nodes">
+ <h3>Blank Nodes</h3>
+
+<p>
+The <dfn title="blank node">blank nodes</dfn> in an RDF graph
+are drawn from an infinite set.
+This set of blank nodes, the set of all <a title="IRI">IRIs</a>
+and the set of all <a title="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>
+
+
+<section id="section-skolemization">
+ <h4>Replacing Blank Nodes with IRIs</h4>
+
+ <p>Blank nodes do not have identifiers in the RDF abstract syntax. The
+ <a title="blank node identifier">blank node identifiers</a> introduced
+ by some concrete syntaxes have only
+ local scope and are purely an artifact of the serialization.</p>
+
+ <p>In situations where stronger identification is needed, systems MAY
+ systematically transform some or all of the blank nodes in an RDF graph
+ into IRIs [[!IRI]]. Systems wishing to do this SHOULD mint a new, globally
+ unique IRI (a <dfn>Skolem IRI</dfn>) for each blank node so transformed.</p>
+
+ <p>This transformation does not change the meaning of an RDF graph,
+ provided that the Skolem IRIs do not occur anywhere else.</p>
+
+ <p>Systems may wish to mint Skolem IRIs in such a way that they can
+ recognize the IRIs as having been introduced solely to replace a blank
+ node, and map back to the source blank node where possible.</p>
+
+ <p>Systems that want Skolem IRIs to be recognizable outside of the system
+ boundaries SHOULD use a well-known IRI [[WELL-KNOWN]] with the registered
+ name <code>genid</code>. This is an IRI that uses the HTTP or HTTPS scheme,
+ or another scheme that has been specified to use well-known IRIs; and whose
+ path component starts with <code>/.well-known/genid/</code>.
+
+ <p>For example, the authority responsible for the domain
+ <code>example.com</code> could mint the following recognizable Skolem IRI:</p>
+
+ <pre>http://example.com/.well-known/genid/d26a2d0e98334696f4ad70a677abc1f6</pre>
+
+ <p class="issue">IETF registration of the <code>genid</code> name is
+ currently in progress.</p>
+
+ <p class="note">RFC 5785 [[WELL-KNOWN]] only specifies well-known URIs,
+ not IRIs. For the purpose of this document, a well-known IRI is any
+ IRI that results in a well-known URI after IRI-to-URI mapping [[!IRI]].</p>
+</section>
+
+</section>
+
+
+<section id="section-multigraph">
+ <h2>Abstract Syntax for Working with Multiple Graphs</h2>
+
+ <div class="issue">
+ <p>The Working Group will standardize a model and semantics for
+ multiple graphs and graphs stores. The
+ <a href="http://www.w3.org/2011/01/rdf-wg-charter">charter</a> notes:</p>
+
+ <blockquote>The RDF Community has used the
+ term “named graphs” for a number of years in various settings,
+ but this term is ambiguous, and often refers to what could rather
+ be referred as quoted graphs, graph literals, IRIs for graphs,
+ knowledge bases, graph stores, etc. The term “Support for Multiple
+ Graphs and Graph Stores” is used as a neutral term in this charter;
+ this term is not and should not be considered as definitive.
+ The Working Group will have to define the right term(s).</blockquote>
+
+ <p>Progress on the design for this feature is tracked under multiple
+ issues:</p>
+
+ <ul>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/5">ISSUE-5: Should we define Graph Literal datatypes?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/14">ISSUE-14: What is a named graph and what should we call it?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/15">ISSUE-15: What is the relationship between the IRI and the triples in a dataset/quad-syntax/etc</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/17">ISSUE-17: How are RDF datasets to be merged?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/22">ISSUE-22: Does multigraph syntax need to support empty graphs?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/28">ISSUE-28: Do we need syntactic nesting of graphs (g-texts) as in N3?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/29">ISSUE-29: Do we support SPARQL's notion of "default graph"?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/30">ISSUE-30: How does SPARQL's notion of RDF dataset relate our notion of multiple graphs?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/32">ISSUE-32: Can we identify both g-boxes and g-snaps?</a></li>
+ <li><a href="http://www.w3.org/2011/rdf-wg/track/issues/33">ISSUE-33: Do we provide a way to refer to sub-graphs and/or individual triples?</a></li>
+ </ul>
+ </div>
+</section>
+
+</section>
+
+
+<section id="section-fragID" class="informative">
+ <h2>Fragment Identifiers</h2>
+
+ <p class="issue">This section does not address the case where RDF is
+ embedded in other document formats, such as in RDFa or when an RDF/XML
+ fragment is embedded in SVG. It has been suggested that this may be
+ a general issue for the TAG about the treatment of
+ fragment identifiers when one language is embedded in another. This is
+ <a href="http://www.w3.org/2011/rdf-wg/track/issues/37">ISSUE-37</a>.</p>
+
+ <p class="issue">This section requires updates to address the
+ change from <a title="RDF URI Reference">URI References</a> to <a title="IRI">IRIs</a>.</p>
+
+ <p>RDF uses an <a title="RDF URI Reference">RDF URI
+ Reference</a>, which may include a fragment identifier, as a
+ context free identifier for a resource. RFC 2396 states that the meaning of a fragment
+ identifier depends on the MIME content-type of a document, i.e.
+ is context dependent.</p>
+ <p>These apparently conflicting views are reconciled by
+ considering that a URI reference in an RDF graph is treated
+ with respect to the MIME type <code>application/rdf+xml</code>
+ [[!RDF-MIME-TYPE]]. 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 <code>application/rdf+xml</code> 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 <code>eg:someurl#frag</code> is used in an RDF
+ document, <code>eg:someurl</code> is taken to
+ designate some RDF document (even when no such document can
+ be retrieved).</li>
+ <li><code>eg:someurl#frag</code> means the thing
+ that is indicated, according to the rules of the
+ <code>application/rdf+xml</code> MIME content-type as
+ a “fragment” or “view” of the RDF document at
+ <code>eg:someurl</code>. If the document does not
+ exist, or cannot be retrieved, or is available only in
+ formats other than <code>application/rdf+xml</code>, then exactly what
+ that view may be is somewhat undetermined, but that does not
+ prevent use of RDF to say things about it.</li>
+ <li>the RDF treatment of a fragment identifier allows it to
+ indicate a thing that is entirely external to the document,
+ or even to the “shared information space” known as the Web.
+ That is, it can be a more general idea, like some particular
+ car or a mythical Unicorn.</li>
+ <li>in this way, an <code>application/rdf+xml</code> document acts as an
+ intermediary between some Web retrievable documents (itself,
+ at least, also any other Web retrievable 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>
+</section>
+
+
+<section id="section-Acknowledgments" class="informative">
+ <h2>Acknowledgments</h2>
+
+ <p class="issue">This section does not yet list those who made
+ contributions to the RDF 1.1 version, nor does it list the
+ current RDF WG members.</p>
+
+ <p>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>
+</section>
+
+
+<section class="appendix informative" id="changes">
+ <h2>Changes from RDF 2004</h2>
+
+ <ul>
+ <li>2011-06-01: Replaced the URI References section with <a href="#section-IRIs">new section on IRIs</a>, and changed “RDF URI Reference” to “IRI” throughout the document, except in <a href="#section-fragID">section 8</a>.</li>
+ <li>2011-06-01: Changed language tag definition to require well-formedness according to BCP47; added a note that this invalidates some RDF</li>
+ <li>2011-05-25: Added boxes for known WG issues throught the document</li>
+ <li>2011-05-25: Deleted “Structure of this Document” section, it added no value beyond the TOC</li>
+ <li>2011-05-25: Implemented resolution of <a href="http://www.w3.org/2011/rdf-wg/track/issues/40">ISSUE-40: Skolemization advice in the RDF dcocument</a> by adding a section on <a href="#section-skolemization">Replacing Blank Nodes with IRIs</a></li>
+ <li>2011-05-25: rdf:XMLLiteral is disjoint from any datatype not explicitly related to it, per erratum <a href="http://www.w3.org/2001/sw/RDFCore/errata#concept-xmlliteral">[concept-xmlliteral]</a></li>
+ <li>2011-05-25: Added Conformance section with RFC2119 reference</li>
+ <li>2011-05-25: Updated all W3C references to latest editions, and Unicode from v3 to v4</li>
+ <li>2011-05-24: Converted to ReSpec, changed metadata to reflect RDF 1.1</li>
+ </ul>
+</section>
+
+
+<section id="references">
+ <div class="issue">
+ <ul>
+ <li>RFC 2279 is obsoleted by RFC 3629</li>
+ <li>Change OWL reference to OWL2?</li>
+ <li>Change XHTML10 reference to XHTML5?</li>
+ </ul>
+ </div>
+</section>
+
+ </body>
+</html>
+
