RDF/XML Syntax Specification (Revised)

W3C Working Draft 8 November 2002

This version:

http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108

Latest version:

http://www.w3.org/TR/rdf-syntax-grammar

Previous versions:

http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20020325

Editor:

Dave Beckett (University of Bristol)

Series editor:

Brian McBride (Hewlett Packard Labs)

Copyright ©2002 W3C^® (MIT, INRIA, Keio), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.

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Abstract

This specification defines an XML syntax for the Resource Description Framework (RDF) as amended and clarified by the RDF Core Working Group from that originally described in RDF Model & Syntax. The syntax is updated to be specified in terms of XML, XML Namespaces, the XML Information Set with new support for XML Base. The parts of the RDF/XML syntax are explained along with examples of how they work. The formal grammar is annotated with actions for generating the arcs that form the RDF graph as defined in the RDF Concepts and Abstract Syntax Working Draft. This is done using the N-Triples RDF Graph serializing format which enables more precise recording of the mapping in a machine processable form. These tests are gathered and published in the RDF Test Cases Working Draft.

Status of this Document

This is a W3C RDF Core Working Group Working Draft produced as part of the W3C Semantic Web Activity (Activity Statement). It incorporates decisions made by the Working Group updating the XML syntax for RDF from the original RDF Model & Syntax [RDF-MS] document in terms of the XML Information Set [INFOSET]. including new support for XML Base, RDF datatyping, rdf:nodeID for referencing Blank Nodes and rdf:parseType="Collection" for expressing a collection of nodes.

This document is being released for review by W3C Members and other interested parties to encourage feedback and comments, especially with regard to how the changes affect existing implementations and content. The current state is that it represents all the syntax as described in the grammar section of the original document, with some removed parts (see rdfms-abouteach), and the mapping to the RDF Graph is considered complete. The detailed changes from the previous 25 March 2002 draft are described in the Changes section however the main changes are as follows: Section 2 An XML syntax for RDF expanded with many more examples of the syntax, support for RDF Typed Literals using rdf:datatype was added, rdf:nodeID was added to allow referencing of Blank Nodes, rdf:parseType="Collection" was added for collections of Nodes, some non-namespaced attributes were returned to the grammar (see section 6.1.4 attribute-uri for the full list) and many other more minor changes after RDF Core Working Group decisions made since the last draft.

This is a public W3C Working Draft and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite as other than "work in progress". A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR/.

There are no known patent or IPR constraints associated with this Working Draft. The RDF Core Working Group Patent Disclosure page contains details, in conformance with W3C policy requirements.

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

1 Introduction

This document defines the XML [XML] syntax for RDF Graphs which was originally defined in the RDF Model & Syntax [RDF-MS] W3C Recommendation. Subsequent implementations of this syntax and comparison of the resulting RDF Graphs have shown that there was ambiguity - implementations generated different graphs and certain syntax forms were not widely implemented. These issues were generally made as either feedback to the www-rdf-comments@w3.org (archive) or from discussions on the RDF Interest Group list www-rdf-interest@w3.org (archive) .

The RDF Core Working Group is chartered to respond to the need for a number of fixes, clarifications and improvements to the specification of RDF's abstract graph and XML syntax. The Working Group invites feedback from the developer community on the effects of its proposals on existing implementations and documents.

Several decisions including amendments and deletions to the grammar are referred to below. The definitive record of the decisions is the RDF Core Working Group issues list.

This document revises the original RDF/XML grammar in terms of XML Information Set [INFOSET] Information Items which moves away from the rather low-level details of XML, such as particular forms of empty elements. This allows the grammar to be more precisely recorded and the mapping from the XML syntax to the RDF Graph more clearly shown. The mapping to the RDF Graph is done by emitting statements in the form defined in the N-Triples section of RDF Test Cases [RDF-TESTS] Working Draft which creates an RDF Graph, that has semantics defined by RDF Semantics [RDF-SEMANTICS] Working Draft.

The complete specification of RDF consists of a number of documents:

• RDF Primer [RDF-PRIMER]
• RDF Concepts and Abstract Syntax [RDF-CONCEPTS]
• RDF Semantics [RDF-SEMANTICS]
• RDF/XML syntax (this document)
• RDF Vocabulary Description Language 1.0: RDF Schema [RDF-VOCABULARY]
• RDF Test Cases [RDF-TESTS]

2 An XML syntax for RDF

This section introduces the RDF/XML syntax, describes how it encodes RDF Graphs and explains this with examples. If there is any conflict between this informal description and the formal description of the syntax and grammar in sections 6 Syntax Data Model and 7 RDF/XML Grammar, the latter two sections take precedence.

2.1 Introduction

The RDF Concepts and Abstract Syntax [RDF-CONCEPTS] working draft defines the RDF Graph data model (Section 2.3.1) and the RDF Graph syntax (Section 4.2). Along with the RDF Semantics [RDF-SEMANTICS] working draft this provides an abstract syntax with a formal semantics for it. The RDF Graph has Nodes and labeled directed Arcs that link pairs of Nodes and this is represented as a set of RDF triples where each triple contains a Subject Node, Property Arc and Object Node. Nodes are RDF URI References, RDF Literals or are Blank Nodes and for encoding in syntaxes may be given a document-local, non-RDF URI References identifier called a Blank Node Identifier. Arcs are labeled with RDF URI References. The property arc can be interpreted as either a relationship between two nodes or as defining an attribute value (object node) for some subject node.

In order to encode the graph in XML, the nodes and arcs have to be represented by XML element names, attribute names, element content and attribute content. RDF/XML uses XML QNames to represent RDF URI References. The namespace prefix part of all QNames is associated with a RDF URI Reference as defined in XML Namespaces [XML-NS]. The RDF URI Reference represented by a QName is determined by appending the local name part of the QName to the RDF URI Reference associated with the namespace prefix part of the QName. This is used to shorten the RDF URI References of all property arcs labels and some nodes. RDF URI References identifying subject and object nodes can also be stored as XML attribute values or XML element names via QNames. RDF Literals (which are only object nodes) become either XML element text content or XML attribute values.

A graph can be considered a collection of paths of the form Node, Arc, Node, Arc, Node, Arc, ... Node which cover the entire graph. In RDF/XML these turn into sequences of elements inside elements which alternate between elements for Nodes and Arcs. This has been called a series of Node/Arc stripes. The Node at the start of the sequence turns into the outermost element, the next arc turns into a child element, and so on. The stripes generally start at the top of an RDF/XML document and always begin with nodes.

Several RDF/XML examples are given in the following sections building up to complete RDF/XML documents. Example 7 is the first complete RDF/XML document.

2.2 Node Elements and Property Elements

Figure 1: Graph for RDF/XML Example (SVG version)

An RDF Graph is given in Figure 1 where the nodes are represented as ovals and contain their RDF URI References where they have them, all the arcs are labeled with RDF URI References and Plain Literal nodes have been written in rectangles.

If we follow one Node, Arc ... , Node path through the graph shown in Figure 2:

Figure 2: One Path Through the Graph (SVG version)

This corresponds to the Node/Arc stripes:

1. Node with RDF URI Reference http://www.w3.org/TR/rdf-syntax-grammar
2. Arc labeled with RDF URI Reference http://example.org/terms/editor
3. Node with no RDF URI Reference
4. Arc labeled with RDF URI Reference http://example.org/terms/homePage
5. Node with RDF URI Reference http://purl.org/net/dajobe/

In RDF/XML, the sequence of 5 nodes and arcs in Figure 2 corresponds to the usage of 5 XML elements of two types, for the graph nodes and arcs. These are conventionally called Node Elements and Property Elements respectively. In the striping shown in Example 1, rdf:Description is the node element (used 3 times for the three nodes) and ex:editor and ex:homePage are the 2 property elements.

The Figure 2 graph consists of some nodes that are RDF URI References (and others that are not) and this can be added to the RDF/XML using the rdf:about attribute on node elements to give the result in Example 2:

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <ex:editor>
    <rdf:Description>
      <ex:homePage>
        <rdf:Description rdf:about="http://purl.org/net/dajobe/">
        </rdf:Description>
      </ex:homePage>
    </rdf:Description>
  </ex:editor>
</rdf:Description>

Adding the other two paths through the Figure 1 graph to the RDF/XML in Example 2 gives the result in Example 3:

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <ex:editor>
    <rdf:Description>
      <ex:homePage>
        <rdf:Description rdf:about="http://purl.org/net/dajobe/">
        </rdf:Description>
      </ex:homePage>
    </rdf:Description>
  </ex:editor>
</rdf:Description>

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <ex:editor>
    <rdf:Description>
      <ex:fullName>Dave Beckett</ex:fullName>
    </rdf:Description>
  </ex:editor>
</rdf:Description>

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <dc:title>RDF/XML Syntax Specification (Revised)</dc:title>
</rdf:Description>

2.3 Multiple Property Elements

There are several abbreviations that can be used to make common uses easier to write down. In particular, it is common that a subject node in the RDF Graph has multiple outgoing arcs. RDF/XML provides an abbreviation for the corresponding syntax when a node element about a resource has multiple property elements. This can be abbreviated by using multiple child property elements inside the node element describing the subject node.

Taking Example 3, there are two node elements that can take multiple property elements. The subject node with URI Reference http://www.w3.org/TR/rdf-syntax-grammar has property elements ex:editor and ex:title and the node element for the blank node can take ex:homePage and ex:fullName. This abbreviation gives the result shown in Example 4:

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <ex:editor>
    <rdf:Description>
      <ex:homePage>
        <rdf:Description rdf:about="http://purl.org/net/dajobe/">
        </rdf:Description>
      </ex:homePage>
      <ex:fullName>Dave Beckett</ex:fullName>
    </rdf:Description>
  </ex:editor>
  <dc:title>RDF/XML Syntax Specification (Revised)</dc:title>
</rdf:Description>

2.4 Empty Property Elements

When an arc in an RDF Graph points to an object node which has no further arcs, which appears in RDF/XML as an empty node element sequence such as the pair <rdf:Description rdf:about="..."> </rdf:Description>, this form can be shortened. This is done by using the RDF URI Reference of the object node as the value of an XML attribute rdf:resource on the containing property element and making the property element empty.

In this example, the property element ex:homePage contains an empty node element with the RDF URI Reference http://purl.org/net/dajobe/. This can be replaced with the empty property element form giving the result shown in Example 5:

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
  <ex:editor>
    <rdf:Description>
      <ex:homePage rdf:resource="http://purl.org/net/dajobe/"/>
      <ex:fullName>Dave Beckett</ex:fullName>
    </rdf:Description>
  </ex:editor>
  <dc:title>RDF/XML Syntax Specification (Revised)</dc:title>
</rdf:Description>

2.5 Property Attributes

When a property element's content is string literal, it may be possible to use it as an XML attribute on the containing node element. This can be done for multiple properties on the same node element only if the property element name is not repeated (required by XML - attribute names are unique on an XML element) and any in-scope xml:lang on the property element's string literal (if any) are the same (see Section 2.7) This abbreviation is known as a Property Attribute and can be applied to any node element or with the rdf:parseType="Resource" form (see Section 2.11).

This abbreviation can also be used when the property element is rdf:type and it has an rdf:resource attribute the value of which is interpreted as a RDF URI Reference object node.

In Example 5:, there are two property elements with string literal content, the dc:title and ex:fullName property elements. These can be replaced with property attributes giving the result shown in Example 6:

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"
                 dc:title="RDF/XML Syntax Specification (Revised)">
  <ex:editor>
    <rdf:Description ex:fullName="Dave Beckett">
      <ex:homePage rdf:resource="http://purl.org/net/dajobe/"/>
    </rdf:Description>
  </ex:editor>
</rdf:Description>

2.6 Completing the Document - Document Element and XML Declaration

To create a complete RDF/XML document, the serialization of the graph into XML must be contained inside an rdf:RDF XML element which becomes the top-level XML document element. Conventionally the rdf:RDF element is also used to declare the XML namespaces that are used, although that is not required. The XML specification also requires an XML declaration at the top of the document with the XML version and possibly the XML content encoding (this is optional but recommended).

This could be done for any of the complete graph examples from Example 3 onwards but taking the smallest Example 6 and adding the final components, gives the complete RDF/XML representation of the original Figure 1 graph in Example 7:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"
		   dc:title="RDF/XML Syntax Specification (Revised)">
    <ex:editor>
      <rdf:Description ex:fullName="Dave Beckett">
	<ex:homePage rdf:resource="http://purl.org/net/dajobe/" />
      </rdf:Description>
    </ex:editor>
  </rdf:Description>
</rdf:RDF>

2.7 Languages - xml:lang

RDF/XML permits the use of the xml:lang attribute as defined by 2.12 Language Identification of XML 1.0 [XML] to allow the identification of content language. This can be used on any node element or property element to indicate that the included content is in the given language. The most specific in-scope language present (if any) is applied to property element string literal content or property attribute values. The xml:lang="" form is used to indicate absence of language.

Some examples of marking content languages for RDF properties are shown in Example 8:

<?xml version="1.0" encoding="iso-8859-1"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/">
  <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar">
    <dc:title>RDF/XML Syntax Specification (Revised)</dc:title>
    <dc:title xml:lang="en">RDF/XML Syntax Specification (Revised)</dc:title>
    <dc:title xml:lang="en-US">RDF/XML Syntax Specification (Revised)</dc:title>
  </rdf:Description>

  <rdf:Description rdf:about="http://example.org/buchen/baum" xml:lang="de">
    <dc:title>Das Baum</dc:title>
    <dc:description>Das Buch ist außergewöhnlich</dc:description>
    <dc:title xml:lang="en">The Tree</dc:title>
  </rdf:Description>
</rdf:RDF>

2.8 XML Literals - rdf:parseType="Literal"

RDF allows XML Literals ([RDF-CONCEPTS] Section 3.2.2) to be given as the object node of arcs. These are written in RDF/XML as content of a property element (not a property attribute) and indicated using the rdf:parseType="Literal" attribute on the containing property element.

An example of writing an XML literal is given in Example 9 where there is a single RDF triple with the subject node RDF URI Reference http://example.org/item01, the arc label RDF URI Reference http://example.org/stuff/1.0/prop (from ex:prop) and the object node with XML Literal content beginning a:Box

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://example.org/item01">
    <ex:prop rdf:parseType="Literal"
             xmlns:a="http://example.org/a#"><a:Box required="true">
         <a:widget size="10" />
         <a:grommit id="23" /></a:Box>
    </ex:prop>
  </rdf:Description>
</rdf:RDF>

2.9 Typed Literals - rdf:datatype

RDF allows Typed Literals to be given as the object node of arcs. These consist of a literal string (with optional language) and a datatype RDF URI Reference. This is handled by using the same syntax for literal string nodes in the property element form (not property attribute) but with an additional rdf:datatype="datatypeURI" attribute on the property element. Any RDF URI Reference can be used in the attribute.

An example of an RDF Typed Literal is given in Example 10 where there is a single RDF triple with the subject node RDF URI Reference http://example.org/item01, the arc label RDF URI Reference http://example.org/stuff/1.0/size (from ex:size) and the object node with the Typed Literal ("123", http://www.w3.org/2001/XMLSchema#int, no language xml:lang="") intending to be interpreted as a W3C XML Schema datatype int.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://example.org/item01">
    <ex:size rdf:datatype="http://www.w3.org/2001/XMLSchema#int">123</ex:size>
  </rdf:Description>
</rdf:RDF>

2.10 Identifying Blank Nodes - rdf:nodeID

Blank Nodes in the RDF Graph are distinct but have no RDF URI Reference identifier. It is sometimes required that the same graph Blank Node is referred to in the RDF/XML in multiple places, such as at the subject and object of several RDF triples. In this case, a Blank Node Identifier can be given to the Blank Node for identifying it in the document. The scope of this identifier is a particular RDF/XML document. A Blank Node Identifier is used on a node element to replace rdf:about="RDF URI Reference" or on a property element to replace rdf:resource="RDF URI Reference" with rdf:nodeID="Blank Node Identifier" in both cases.

Taking Example 7 and explicitly giving a Blank Node Identifier of abc to the blank node in it gives the result shown in Example 11. The second rdf:Description property element is about the blank node.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"
		   dc:title="RDF/XML Syntax Specification (Revised)">
    <ex:editor rdf:nodeID="abc"/>
  </rdf:Description>

  <rdf:Description rdf:nodeID="abc"
                   ex:fullName="Dave Beckett">
    <ex:homePage rdf:resource="http://purl.org/net/dajobe/"/>
  </rdf:Description>
</rdf:RDF>

2.11 Omitting Blank Nodes - rdf:parseType="Resource"

Blank Nodes (no resource RDF URI Reference) in RDF Graphs can be written in a form that allows the <rdf:Description> </rdf:Description> pair to be omitted. This can be done by putting an attribute on the containing property element rdf:parseType="Resource" that turns the property element into a property and node element, which can itself have both property elements and property attributes.

Taking the earlier Example 7, the contents of the ex:editor property element could be alternatively done in this fashion to give the form shown in Example 12:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"
		   dc:title="RDF/XML Syntax Specification (Revised)">
    <ex:editor rdf:parseType="Resource">
      <ex:fullName>Dave Beckett</ex:fullName>
      <ex:homePage rdf:resource="http://purl.org/net/dajobe/"/>
    </ex:editor>
  </rdf:Description>
</rdf:RDF>

2.12 Omitting Blank Nodes - Property Attributes on an empty Property Element

If all of the property elements on a blank node element have string literal values with the same in-scope xml:lang value (if present) and each of these property elements appears at most once and there is at most one rdf:type property element with a RDF URI Reference object node, these can be abbreviated by moving them to be property attributes on the containing property element which is made an empty element.

Taking the earlier Example 5, the ex:editor property element contains a blank node element with two property elements ex:fullname and ex:homePage. ex:homePage is not suitable here since it does not have a string literal value, so it is being ignored. The abbreviated form moves ex:fullName property element to be a property attribute on the ex:editor property element and the blank node element becomes implicit. The result is shown in Example 13.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"
		   dc:title="RDF/XML Syntax Specification (Revised)">
    <ex:editor ex:fullName="Dave Beckett" />
    <!-- Note the ex:homePage property has been ignored for this example -->
  </rdf:Description>
</rdf:RDF>

2.13 Typed Node Elements

It is common for RDF Graphs to have rdf:type arcs from subject nodes. These are conventionally called Typed Nodes in the graph, or Typed Node Elements in the RDF/XML. RDF/XML allows this triple to be expressed more concisely. by replacing the rdf:Description node element name with the namespaced-element corresponding to the RDF URI Reference of the value of the type relationship. There may, of course, be multiple rdf:type arcs but only one can be used in this way, the others must remain as property elements or property attributes.

This form is also commonly used in RDF/XML with the built-in classes in The RDF Namespace: rdf:Seq, rdf:Bag, rdf:Alt, rdf:Statement, rdf:Property and rdf:List.

For example, the RDF/XML in Example 14 could be written as shown in Example 15.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://example.org/thing">
    <rdf:type rdf:resource="http://example.org/stuff/1.0/Document"/>
    <dc:title>A marvelous thing</dc:title>
  </rdf:Description>
</rdf:RDF>

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <ex:Document rdf:about="http://example.org/thing">
    <dc:title>A marvelous thing</dc:title>
  </ex:Document>
</rdf:RDF>

2.14 Abbreviating URIs - rdf:ID and xml:base

RDF/XML allows further abbreviating RDF URI References in XML attributes in two ways. The XML Infoset provides a base URI attribute xml:base that sets the base URI for resolving relative RDF URI References, otherwise the base URI is that of the document. This applies to all RDF/XML attributes that deal with RDF URI References which are rdf:about, rdf:resource, rdf:ID, rdf:bagID and rdf:datatype.

The rdf:ID attribute on a node element (not property element, that has another meaning) can be used instead of rdf:about and gives a relative RDF URI Reference equivalent to # concatenated with the rdf:ID attribute value. So for example if rdf:ID="name", that would be equivalent to rdf:about="#name". This provides an additional check since the same name can only appear once in the scope of an xml:base value (or document, if none is given), so is useful for defining a set of distinct, related terms relative to the same RDF URI Reference.

Example 16 shows abbreviating the node RDF URI Reference of http://example.org/here/#snack using an xml:base of http://example.org/here/ and an rdf:ID on the rdf:Description node element. The object node of the ex:prop arc is an absolute RDF URI Reference resolved from the rdf:resource XML attribute content using the in-scope base URI to give the RDF URI Reference http://example.org/here/fruit/apple.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ex="http://example.org/stuff/1.0/"
         xml:base="http://example.org/here/">
  <rdf:Description rdf:ID="snack">
    <ex:prop rdf:resource="fruit/apple"/>
  </rdf:Description>
</rdf:RDF>

2.15 Container membership property elements - rdf:li and rdf:_n

RDF has a set of container membership properties and corresponding property elements that are mostly used with instances of the rdf:Seq, rdf:Bag and rdf:Alt classes which may be written as typed node elements. The list properties are rdf:_1, rdf:_2 etc. and can be written as property elements or property attributes as shown in Example 17. There is an rdf:li special property element that is equivalent to rdf:_1, rdf:_2 in order, explained in detail in section 7.4. The equivalent RDF/XML to Example 17 written in this form is shown in Example 18.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Seq rdf:about="http://example.org/favourite-fruit">
    <rdf:_1 rdf:resource="http://example.org/banana"/>
    <rdf:_2 rdf:resource="http://example.org/apple"/>
    <rdf:_3 rdf:resource="http://example.org/pear"/>
  </rdf:Seq>
</rdf:RDF>

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Seq rdf:about="http://example.org/favourite-fruit">
    <rdf:li rdf:resource="http://example.org/banana"/>
    <rdf:li rdf:resource="http://example.org/apple"/>
    <rdf:li rdf:resource="http://example.org/pear"/>
  </rdf:Seq>
</rdf:RDF>

2.16 Collections - rdf:parseType="Collection"

RDF/XML allows an rdf:parseType="Collection" attribute on a property element to let it contain multiple node elements. These contained node elements give the set of subject nodes of the collection. This syntax form corresponds to a set of triples about the collection of subject nodes, the exact triples generated are described in detail in Section 7.2.19 Production parseTypeCollectionPropertyElt.

Example 19 shows a collection of three nodes elements at the end of the ex:hasFruit property element using this form.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://example.org/basket">
    <ex:hasFruit rdf:parseType="Collection">
      <rdf:Description rdf:about="http://example.org/banana"/>
      <rdf:Description rdf:about="http://example.org/apple"/>
      <rdf:Description rdf:about="http://example.org/pear"/>
    </ex:hasFruit>
  </rdf:Description>
</rdf:RDF>

2.17 Reifying Statements - rdf:bagID and rdf:ID

The rdf:ID attribute can be used on a property element to reify the triple that it generates (See section 7.3 Reification Rules for the full details). The identifier for the triple should be constructed as a RDF URI Reference made from the relative URI Reference # concatenated with the rdf:ID attribute value, resolved against the in-scope base URI. So for example if rdf:ID="triple", that would be equivalent to the RDF URI Reference formed from relative URI Reference #triple against the base URI. Each (rdf:ID attribute value, base URI) pair has to be unique in an RDF/XML document and comes from the same set of values as the rdf:bagID attribute. See constraint-id.

Example 20 shows a rdf:ID being used to reify a triple made from the ex:prop property element giving the reified triple the RDF URI Reference http://example.org/triples/#triple1.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ex="http://example.org/stuff/1.0/"
         xml:base="http://example.org/triples/">
  <rdf:Description rdf:about="http://example.org/">
    <ex:prop rdf:ID="triple1">blah</ex:prop>
  </rdf:Description>
</rdf:RDF>

The rdf:bagID attribute can be used on a node element or empty property element with property attributes, to give an identifier for a rdf:Bag that lists the statements generated by the property elements or attributes. This allows statements to be made about that bag. The identifier is constructed as a relative RDF URI Reference of # concatenated with the rdf:bagID attribute value, resolved against the in-scope base URI to give an RDF URI Reference. So for example if rdf:bagID="bag", that would be equivalent to the RDF URI Reference formed from relative URI Reference #bag against the base URI. Each (rdf:bagID attribute value, base URI) has to be unique in the RDF/XML document and from the same set of names as rdf:ID. See constraint-id.

Example 21 shows a rdf:Bag with RDF URI Reference http://example.org/bags/#bag1 being made of the triples from inside the rdf:Description node element.

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ex="http://example.org/stuff/1.0/"
         xml:base="http://example.org/bags/">
  <rdf:Description rdf:about="http://example.org/" rdf:bagID="bag1">
    <ex:prop1>blah</ex:prop1>
    <ex:prop2 rdf:resource="http://example.org/elsewhere/"/>
  </rdf:Description>
</rdf:RDF>

2.18 More Information (Informative)

The RDF Core Working Group has developed an RDF Primer [RDF-PRIMER] that goes into detail introducing RDF and its applications.

For a longer introduction to the RDF/XML striped syntax with a historical perspective, see RDF: Understanding the Striped RDF/XML Syntax [STRIPEDRDF].

3 Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [KEYWORDS].

4 RDF MIME type, file extension and Macintosh file type

The Internet Media Type / MIME type for RDF is "application/rdf+xml" - see RFC 3032 (RFC-3023) section 8.18.

It is recommended that RDF files have the extension ".rdf" (all lowercase) on all platforms.

It is recommended that RDF files stored on Macintosh HFS file systems be given a file type of "rdf " (all lowercase, with a space character as the fourth letter).

5 Global Issues

5.1 The RDF Namespace

The RDF Namespace URI Reference is http://www.w3.org/1999/02/22-rdf-syntax-ns# and is typically used in XML with the prefix rdf although other prefix strings may be used. The namespace contains the following names only:

Syntax names - not concepts

RDF Description ID about bagID parseType resource li nodeID datatype

Class names

Seq Bag Alt Statement Property List

Property names

subject predicate object type value first rest _n
where n is an integer greater than zero.

Resource names

nil

Any other names are not defined and SHOULD generate a warning when encountered, but should otherwise behave normally.

Throughout this document the terminology rdf:name will be used to indicate name is from the RDF namespace and it has a RDF URI Reference of the concatenation of the ·RDF Namespace URI Reference· and name. For example, rdf:type has the RDF URI Reference http://www.w3.org/1999/02/22-rdf-syntax-ns#type

5.2 Identifiers

The RDF Graph (RDF Concepts and Abstract Syntax Section 3) defines three types of nodes and one type of arcs:

RDF URI Reference nodes and arcs

RDF URI References (RDF Concepts and Abstract Syntax Section 3.1) can be either given as XML attribute values interpreted as absolute RDF URI References, XML attribute values interpreted as relative URI References that are resolved to the in-scope base URI as described in section section 5.3 to give absolute RDF URI References, transformed from XML Namespace-qualified element and attributes names (QNames) or transformed from rdf:ID and rdf:bagID attribute values.

Within RDF/XML, XML QNames are transformed into RDF URI References by appending the XML local name to the namespace URI. For example, if the XML Namespace prefix foo has URI http://example.org/somewhere/ then the QName foo:bar would correspond to the URI http://example.org/somewhere/bar. Note that this restricts which RDF URI References can be made and the same URI can be given in multiple ways.

The rdf:ID and rdf:bagID values are transformed into an RDF URI References by appending the attribute value to the result of appending "#" to the in-scope base URI which is defined in Section 5.3 Base URIs

Literal nodes (always object nodes)

RDF Literals (RDF Concepts and Abstract Syntax 3.2) are either Plain Literals (ibid section 2.3.4), or Typed Literals (ibid section 2.3.4). The latter includes XML Literals (ibid section 3).

Blank Node Identifiers

The Blank Nodes have distinct identity in the RDF Graph. When the graph is encoded in a syntax such as RDF/XML, these Blank Nodes may need temporary concrete identifiers which have restrictions on the syntax that can be used, but these are not required for the graph. Blank Node Identifiers are used in RDF/XML as values of the rdf:datatype attribute for such local identification of these nodes. See section 7.2.28 Production datatypeAttr.

5.3 Base URIs

RDF/XML supports XML Base [XML-BASE] which defines a ·base-uri· accessor for each ·root event· and ·element event·. Relative URI References are resolved into RDF URI References according to the algorithm specified in XML Base [XML-BASE] (and RFC 2396). These specifications do not specify an algorithm for resolving a fragment identifier alone, such as #foo, or the empty string "" into an RDF URI Reference. In RDF/XML, a fragment identifier is transformed into a RDF URI Reference by appending the fragment identifier to the in-scope base URI. The empty string is transformed into an RDF URI Reference by substituting the in-scope base URI.

An empty same document reference "" resolves against the URI part of the Base URI; any fragment part is ignored. See Uniform Resource Identifiers (URI) [URIS] section 4.2

5.4 Constraints

constraint-id

Each application of productions idAttr and bagIdAttr match an attribute. The pair formed by the ·string-value· accessor of the matched attribute and the ·base-uri· accessor of the matched attribute is unique within a single RDF/XML document.

The syntax of the names must match the rdf-id production

Test: Indicated by test014.rdf and test014.nt

6 Syntax Data Model

This document specifies the syntax of RDF/XML as a grammar on an alphabet of symbols. The symbols are called Events in the style of the [XPATH]  Information Set Mapping. A sequence of events is normally derived from an XML document, in which case they are in document order as defined below in Section 6.2 Information Set Mapping. This sequence of events formed are intended to be similar to the sequence of events produced by the [SAX2] XML API from the same XML document. Sequences of events may be checked against the grammar to determine whether they are or are not syntactically well formed RDF/XML.

The grammar productions may include actions which fire when the production is recognised. Taken together these actions define a transformation from any syntactically well formed RDF/XML sequence of events into an RDF Graph represented in the N-Triples language.

This model illustrates one way to create a representation of an RDF Graph from an RDF/XML document. It does not mandate any implementation method - any other method that results in a representation of the same RDF Graph may be used.

In particular:

• This specification does not require that N-Triples be used to represent an RDF Graph.
• This specification does not require the use of [XPATH] or [SAX2]
• This specification places no constraints on the order in which software transforming RDF/XML into a representation of a graph, constructs the representation of the graph.
• Software transforming RDF/XML into a representation of a graph MAY eliminate duplicate arcs.

The syntax does not support non-well-formed XML documents, nor documents that otherwise do not have an XML Information Set; for example, that do not conform to XML Namespaces [XML-NS].

The Infoset requires support for XML Base [XML-BASE]. RDF/XML uses the information item property [base URI], discussed in section 5.3

This specification requires an XML Information Set[INFOSET] which supports at least the following information items and properties for RDF/XML:

Document Information Item

[document element], [children], [base URI]

Element Information Item

[local name], [namespace name], [children], [attributes], [parent], [base URI]

Attribute Information Item

[local name], [namespace name], [normalized value]

Character Information Item

[character code]

There is no mapping of the following items to data model events:

Processing Instruction Information Item

Unexpanded Entity Reference Information Item

Comment Information Item

Document Type Declaration Information Item

Unparsed Entity Information Item

Notation Information Item

Namespace Information Item

Other information items and properties have no mapping to syntax data model events.

Information items contained inside XML elements matching the parseTypeLiteralPropertyElt production form XML Literals and do not follow this mapping. See the [RDF-CONCEPTS] section on XML Literals for further information.

This section is intended to satisfy the requirements for Conformance in the [INFOSET] specification. It specifies the information items and properties that are needed to implement this specification.

6.1 Events

There are six types of event defined in the following subsections. Most events are constructed from an Infoset information item (except for Identifier, Plain Literal and XML Literal). The effect of an event constructor is to create a new event with a unique identity, distinct from all other events. Events have accessor operations on them. and all have the string-value accessor that may be a static value or computed.

6.1.1 Root Event

Constructed from a Document Information Item and takes the following accessors and values.

document-element

Set to the value of document information item property document-element.

children

Set to the value of document information item property [children].

base-uri

Set to the value of document information item property [base URI].

language

Set to the empty string.

6.1.2 Element Event

Constructed from an Element Information Item and takes the following accessors and values:

local-name

Set to the value of element information item property [local name].

namespace-name

Set to the value of element information item property [namespace name].

children

Set to the value of element information item property [children].

base-uri

Set to the value of element information item property [base URI].

attributes

Set to the value of element information item property [attributes].

If the value contains an attribute event xml:lang (that is, the ·local-name· accessor of the attribute has value "lang" and the ·namespace-name· accessor of the attribute has value "http://www.w3.org/XML/1998/namespace"), it is removed from the list of attributes and the ·language· accessor is set to the string-value of the attribute.

All other attributes beginning with xml are then removed (that is, all attributes with ·namespace-name· accessors values beginning with "http://www.w3.org/XML/1998/namespace"). Note: the base URI is computed before any xml:base attribute is deleted.

URI

Set to the string value of the concatenation of the value of the namespace-name accessor and the value of the local-name accessor.

li-counter

Set to the integer value 1.

bag-li-counter

set to the integer value 1.

language

Set from the ·attributes· as described above. If no value is given from the attributes, the value is set to the value of the language accessor on the parent event (either a Root Event or an Element Event), which may be the empty string.

subject

Has no initial value. Takes a value that is an Identifier event. This is used on elements that deal with one node in the RDF Graph, this generally being the subject of a statement.

6.1.3 End Element Event

Has no accessors. Marks the end of the containing element in the sequence.

6.1.4 Attribute Event

Constructed from an Attribute Information Item and takes the following accessors and values:

local-name

Set to the value of attribute information item property [local name].

namespace-name

Set to the value of attribute information item property [namespace name].

string-value

set to the value of the attribute information item property [normalized value] as specified by [XML] (if an attribute whose normalized value is a zero-length string, then the string-value is also a zero-length string).

URI

If ·namespace-name· is present, set to a string value of the concatenation of the value of the ·namespace-name· accessor and the value of the ·local-name· accessor. Otherwise if ·local-name· is ID, bagID, about, resource, parseType or type, set to a string value of the concatenation of the ·RDF Namespace URI Reference· and the value of the ·local-name· accessor. Other non-namespaced ·local-name· accessor values are forbidden.

NOTE: This support for a limited set of non-namespaced names is REQUIRED and intended to allow RDF/XML documents specified in [RDF-MS] to remain valid; new documents SHOULD NOT use these unqualified attributes and applications MAY choose to warn when the unqualified form is seen in a document.

NOTE: The construction of RDF URI References from XML attributes can generate the same RDF URI References from different XML attributes. This can cause ambiguity in the grammar when matching attribute events (such as when rdf:about and about XML attributes are both present). Documents that have this are illegal. How this is forbidden will will be addressed and explained in more detail in the next version of this working draft.

6.1.5 Text Event

Constructed from a sequence of one or more consecutive Character Information Items. Has the single accessor:

string-value

Set to the value of the string made from concatenating the [character code] property of each of the character information items.

6.1.6 Identifier Event

A node for a typed identifier which has the following accessors:

identifier

Takes a string value.

identifier-type

Takes one of the two values "URI" or "bnodeID"

string-value

The value of this is calculated from the other accessors based on the ·identifier-type· value as follows.

When "URI", the value is the concatenation of "<", the value of the ·identifier· accessor and ">"

Otherwise ("bnodeID"), the value is the concatenation of "_:" and the value of the ·identifier· accessor.

These events are constructed by giving two values for the ·identifier· and ·identifier-type· accessors.

For further information on identifiers in the RDF Graph, see section 5.2.

6.1.7 Plain Literal Event

An event for a text literal which can have the following accessors:

literal-value

Takes a string value.

literal-language

Takes a string value.

literal-datatype

Takes an optional string value used as a URI.

string-value

The value is calculated from the other accessors as follows.

If ·literal-language· is the empty string then the value is the concatenation of """ (1 double quote), the value of the 2 ·literal-value· accessor and """ (1 double quote).

Otherwise the value is the concatenation of """ (1 double quote), the value of the ·literal-value· accessor ""@" (1 double quote and a '@'), and the value of the ·literal-language· accessor.

If ·literal-datatype· is not empty then append to the value calculated above "^^<" concatenated with the value of the ·literal-datatype· accessor concatenated with ">".

Note that the double-quoted ·literal-value· string must use the N-Triples string escapes for escaping certain characters such as ".

These events are constructed by giving values for the ·literal-value· and ·literal-language· accessors.

6.1.8 XML Literal Event

An event for an XML literal which can have the following accessors:

literal-value

Takes a string value.

literal-language

Takes a string value.

string-value

The value is calculated from the other accessors as follows.

If ·literal-language· is the empty string then the value is the concatenation of """ (1 double quote), the value of the ·literal-value· accessor and ""^^<http://www.w3.org/2000/01/rdf-schema#XMLLiteral>" (1 double quote).

Otherwise the value is the concatenation of """ (1 double quote), the value of the ·literal-value· accessor ""@" (1 double quote and a '@'), the value of the ·literal-language· accessor and "^^<http://www.w3.org/2000/01/rdf-schema#XMLLiteral>".

Note that the double-quoted literal-value string must use the N-Triples string escapes for escaping certain characters such as ".

These events are constructed by giving values for the ·literal-value· and ·literal-language· accessors.

6.2 Information Set Mapping

To transform the Infoset into the sequence of events in document order, each information item is transformed as described above to generate a tree of events with accessors and values. Each element event is then replaced as described below to turn the tree of events into a sequence in document order.

1. The original element event
2. The value of the children accessor recursively transformed, a possibly empty ordered list of events.
3. An end element event

6.3 Grammar Notation

The following notation is used for matching the sequence of events generated as described in Section 6 and describing the actions to perform for the matches. The RDF/XML grammar is defined here in terms of its data model events, using statements of the form:

number event-type event-content

action...

N-Triples

where the event-content is an expression, which may refer to other event-types (as defined in Section 6.1), using constructs of the form given in the following table. The number is used for reference purposes. The action may include generating new triples to the graph, written in N-Triples format.

7 RDF/XML Grammar

7.1 Grammar summary

7.2 Grammar Productions

7.2.1 Grammar start

If the RDF/XML is a standalone XML document (known by having been given the RDF MIME Type) then the grammar starts with Root Event  doc.

If the content is known to be RDF/XML by context, such as when RDF/XML is embedded inside other XML content, then the grammar can either start at Element Event  RDF (only when an element is legal at that point in the XML) or at production nodeElementList (only when element content is legal, since this is a list of elements). For such embedded RDF/XML, the ·base-uri· value on the outermost element must be initialized from the containing XML since no Root Event  will be available. Note that if such embedding occurs, the grammar may be entered several times but no state is expected to be preserved.

7.2.2 Production coreSyntaxTerms

A subset of the syntax terms from the RDF Namespace in section 5.1 which are are used in RDF/XML.

7.2.3 Production syntaxTerms

All the syntax terms from the RDF Namespace in section 5.1 which are used in the RDF/XML.

7.2.4 Production oldTerms

These are the names from the RDF Namespace that have been withdrawn from the language. See the resolutions of the rdfms-aboutEach-on-object and rdfms-abouteachprefix issues for further information.

7.2.5 Production nodeElementURIs

The RDF URI References that are allowed on node elements.

7.2.6 Production propertyElementURIs

The URIS that are allowed on property elements.

7.2.7 Production propertyAttributeURIs

The RDF URI References that are allowed on property attributes.

7.2.8 Production doc

7.2.9 Production RDF

7.2.10 Production nodeElementList

7.2.11 Production nodeElement

For node element e, the processing of some of the attributes has to be done before other work such as dealing with children events or other attributes. These can be processed in any order:

• If there is an attribute a with a.URI == rdf:ID, then e.subject := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI").
• If there is an attribute a with a.URI == rdf:nodeID, then e.subject := identifier(identifier:=a.string-value, identifier-type:="bnodeID").
• If there is an attribute a with a.URI == rdf:about then e.subject := identifier(identifier := a.string-value, identifier-type:="URI").

If e.subject is empty, generate a Blank Node Identifier i and n := identifier(identifier := i, identifier-type:="bnodeID"). Then e.subject := n.

The following can then be performed in any order:

• S1 If e.URI != rdf:Description then the following statement is added to the graph:

  e.subject.string-value <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <e.URI> .

• S2 If there is an attribute a in propertyAttr with a.URI == rdf:type then the following statement is added to the graph:

  e.subject.string-value <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <a.string-value> .

• S3 For each attribute a matching propertyAttr (and not rdf:type) then o := literal(literal-value := a.string-value, literal-language := e.language) and the following statement is added to the graph:

  e.subject.string-value <a.URI> o.string-value .

• S4 Handle the propertyEltList children events in document order.

If an attribute a with a.URI == rdf:bagID is present, n := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI") then in any order:

• S5 Add the following statement to the graph:

  n.string-value <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Bag> .

• For the generated statements above (excluding S5) in the following order

  1. S1
  2. Statements from S2 and S3 in any order
  3. Statements generated by the propertyEltList children by S4 in document order

  If the statement was generated by S4 from a propertyElt and has an existing identifier e.subject then s := e.subject. Otherwise generate a Blank Node Identifier i and s := identifier(identifier := i, identifier-type:="bnodeID")

  Then reify the statement with identifier event s using the reification rules in section 7.3 and apply the bag expansion rules in section 7.5 on event n to give a URI u. Then the following statement is added to the graph:

  n.string-value <u> s.string-value .

7.2.12 Production ws

7.2.13 Production propertyEltList

7.2.14 Production propertyElt

If element e has e.URI = rdf:li then apply the list expansion rules on element e.parent in section 7.4 to give a new URI u and e.URI := u.

NOTE: The action of this production must be done before the actions of any sub-matches (resourcePropertyElt ... emptyPropertyElt). Alternatively the result must be equivalent to as if it this action was performed first, such as performing as the first action of all of the sub-matches.

7.2.15 Production resourcePropertyElt

For element e, and the single contained nodeElement n the following statement is added to the graph:

If the rdf:ID attribute a is given, the above statement is reified with i := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI") using the reification rules in section 7.3 and e.subject := i

7.2.16 Production literalPropertyElt

For element e, and the text event t. If the rdf:datatype attribute d is given then o := literal(literal-value := t.string-value, literal-language := e.language, literal-datatype := a.string-value) otherwise o := literal(literal-value := t.string-value, literal-language := e.language) and the following statement is added to the graph:

If the rdf:ID attribute a is given, the above statement is reified with i := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI") using the reification rules in section 7.3 and e.subject := i.

7.2.17 Production parseTypeLiteralPropertyElt

For element e and the literal l, then o := xml(literal-value := l.string-value, literal-language := e.language) and the following statement is added to the graph:

If the rdf:ID attribute a is given, the above statement is reified with i := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI") using the reification rules in section 7.3 and e.subject := i.

The result of a literal from rdf:parseType="Literal" content is an XML Literal. See the [RDF-CONCEPTS] section on XML Literals for further information.

7.2.18 Production parseTypeResourcePropertyElt

For element e with possibly empty element content c.

generate a Blank Node Identifier i and n := identifier(identifier := i, identifier-type:="bnodeID").

Add the following statement to the graph:

If the rdf:ID attribute a is given, the statement above is reified with i := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI") using the reification rules in section 7.3 and e.subject := i.

If the element content c is not an empty, then use event n to create a new sequence of events as follows:

Then process the resulting sequence using production nodeElement.

7.2.19 Production parseTypeCollectionPropertyElt

For element event e with possibly empty nodeElementList l. Set s:=list().

For each element event f in l, generate a Blank Node Identifier i, n := identifier(identifier := i, identifier-type:="bnodeID") and append n to s to give a sequence of identifier events.

If s is not empty, n is the first event identifier in s and the following statement is added to the graph:

otherwise the following statement is added to the graph:

If the rdf:ID attribute a is given, the above statement is reified with i := identifier(identifier:=concat(e.base-uri, "#", a.string-value), identifier-type:="URI") using the reification rules in section 7.3.

If s is empty, no further work is performed.

For each identifier event n in s, the following statement is added to the graph:

For each identifier event n in s and the corresponding element event f in l, the following statement is added to the graph:

For each consecutive, overlapping pairs of identifier events (n, o) in s, the following statement is added to the graph:

If s is not empty, n is the last event identifier in s, the following statement is added to the graph:

7.2.20 Production parseTypeOtherPropertyElt

All rdf:parseType attribute values other than the strings "Resource", "Literal" or "Collection" are treated as if the value was "Literal". This production matches and acts as if production parseTypeLiteralPropertyElt was matched. No extra triples are generated for other rdf:parseType values.

7.2.21 Production emptyPropertyElt

• If there are no attributes or only the optional rdf:ID attribute i then o := literal(literal-value:="", literal-language := e.language) and the following statement is added to the graph:

  e.parent.subject.string-value <e.URI> o.string-value .

  and then if i is given, the above statement is reified with identifier(identifier:=concat(e.base-uri, "#", i.string-value), identifier-type:="URI") using the reification rules in section 7.3.

  Test: Indicated by test002.rdf and test002.nt

  Test: Indicated by test005.rdf and test005.nt

• Otherwise

  • If rdf:resource attribute i is present, then r := identifier(identifier := i.string-value, identifier-type:="URI")
  • If rdf:nodeID attribute i is present, then r := identifier(identifier := i.string-value, identifier-type:="bnodeID")
  • If neither, generate a Blank Node Identifier i and r := identifier(identifier := i, identifier-type:="bnodeID")

  If optional rdf:bagID attribute b is given, n := identifier(identifier:=concat(e.base-uri, "#", b.string-value), identifier-type:="URI")

  The following are done in any order:

  • Add the following statement to the graph:

    e.parent.subject.string-value <e.URI> r.string-value .

    and then if rdf:ID attribute i is given, the above statement is reified with identifier(identifier:=concat(e.base-uri, "#", i.string-value), identifier-type:="URI") using the reification rules in section 7.3.

  • For all propertyAttr attributes a (in any order)

    • If a.URI == rdf:type then the following statement is added to the graph:

      r.string-value <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <a.string-value> .

    • Otherwise o := literal(literal-value := a.string-value, literal-language := e.language) and the following statement is added to the graph:

      r.string-value <a.URI> o.string-value .

    If Identifier event n was created, then for each statement above: generate a Blank Node Identifier i, s := identifier(identifier := i, identifier-type:="bnodeID"), reify the statement with identifier event i using the reification rules in section 7.3, apply the bag expansion rules in section 7.5 on event n to give URI u and add the following statement is added to the graph:

    n.string-value <u> s.string-value; .

    Test: Indicated by test013.rdf and test013.nt

    Test: Indicated by test014.rdf and test014.nt

  • If Identifier event n was created, add the following statement to the graph:

    n.string-value <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Bag> .

7.2.22 Production idAttr

Constraint:: constraint-id applies to the values of rdf:ID attributes

7.2.23 Production nodeIdAttr

7.2.24 Production aboutAttr

7.2.25 Production bagIdAttr

Constraint:: constraint-id applies to the values of rdf:bagID attributes

7.2.26 Production propertyAttr

7.2.27 Production resourceAttr

7.2.28 Production datatypeAttr

7.2.29 Production parseLiteral

7.2.30 Production parseResource

7.2.31 Production parseCollection

7.2.32 Production parseOther

7.2.33 Production URI-reference

7.2.34 Production literal

7.2.35 Production rdf-id

7.3 Reification Rules

For a statement with terms s, p and o corresponding to the N-Triples:

add the following statements to the graph using the given Identifier Event r:

7.4 List Expansion Rules

For the given element e, create a new RDF URI Reference u := concat("http://www.w3.org/1999/02/22-rdf-syntax-ns#_", e.li-counter), increment the e.li-counter property by 1 and return u.

7.5 Bag Expansion Rules

For the given element e, create a new RDF URI Reference u := concat("http://www.w3.org/1999/02/22-rdf-syntax-ns#_", e.bag-li-counter), increment the e.bag-li-counter property by 1 and return u.

8 Serializing an RDF Graph to RDF/XML

There are some RDF Graphs as defined in the RDF Concepts and Abstract Syntax Working Draft. that cannot be serialized in RDF/XML. These are those that:

Use property names that cannot be turned into XML namespace-qualified names.

An XML namespace-qualified name (QName) has restrictions on the legal characters such that not all property URIs can be expressed as these names. It is recommended that implementors of RDF serializers, in order to break a URI into a namespace name and a local name, split it after the last XML non-NCName character, ensuring that the first character of the name is a Letter or '_'. If the URI ends in a non-NCName character then throw a "this graph cannot be serialized in RDF/XML" exception or error.

Use inappropriate reserved names as properties

For example, a property with the same URI as any of the syntaxTerms production.

A more detailed discussion of the issues of serializing the RDF Graph to RDF/XML is given in [UNPARSING]. This describes using the original syntax without the subsequently added rdf:nodeID attribute that now allows all graphs with blank nodes to be serialized.

9 Using RDF/XML with HTML and XHTML

If RDF/XML is embedded inside HTML or XHTML this can add many new elements and attributes, many of which will not be in the appropriate DTD. This causes validation against the DTD to fail. The obvious solution of changing or extending the DTD is not practical for most uses. This problem has been analyzed extensively by Sean B. Palmer in RDF in HTML: Approaches[RDF-IN-XHTML] and it concludes that there is no single embedding method that satisfies all applications and remains simple.

The recommended approach is to not embed RDF/XML in HTML/XHTML but rather to use <link> element in the <head> element of the HTML/HTML to point at a separate RDF/XML document. This has been used for several years by the Dublin Core Metadata Initiative (DCMI) on its Web site.

To use this technique, the <link> element href should point at the URI of the RDF/XML content and the type attribute should be used with the value of "application/rdf+xml", the proposed MIME Type for RDF/XML, see Section 4

The value of the rel attribute may also be set to indicate the relationship; this is an application dependent value. The DCMI has used and recommended rel="meta" when linking in RFC 2731 - Encoding Dublin Core Metadata in HTML[RFC-2731] however rel="alternative" may also be appropriate. See HTML 4.01 link types and XHTML Modularization - LinkTypes for further information.

10 Acknowledgments (Informative)

The following people provided valuable contributions to the document:

• Dan Brickley, W3C/ILRT
• Jeremy Carroll, HP Labs Bristol
• Bijan Parsia, MIND Lab at University of Maryland at College Park

This document is a product of extended deliberations by the RDF Core working group, whose members have included: Art Barstow (W3C) Dave Beckett (ILRT), Dan Brickley (W3C/ILRT), Dan Connolly (W3C), Jeremy Carroll (Hewlett Packard), Ron Daniel (Interwoven Inc), Bill dehOra (InterX), Jos De Roo (AGFA), Jan Grant (ILRT), Graham Klyne (Clearswift and Nine by Nine), Frank Manola (MITRE Corporation), Brian McBride (Hewlett Packard), Eric Miller (W3C), Stephen Petschulat (IBM), Patrick Stickler (Nokia), Aaron Swartz (HWG), Mike Dean (BBN Technologies / Verizon), R. V. Guha (Alpiri Inc), Pat Hayes (IHMC), Sergey Melnik (Stanford University), Martyn Horner (Profium Ltd).

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: Nick Arnett (Verity), Tim Berners-Lee (W3C), Tim Bray (Textuality), Dan Brickley (ILRT / University of Bristol), Walter Chang (Adobe), Sailesh Chutani (Oracle), Dan Connolly (W3C), Ron Daniel (DATAFUSION), Charles Frankston (Microsoft), Patrick Gannon (CommerceNet), RV Guha (Epinions, previously of Netscape Communications), Tom Hill (Apple Computer), Arthur van Hoff (Marimba), Renato Iannella (DSTC), Sandeep Jain (Oracle), Kevin Jones, (InterMind), Emiko Kezuka (Digital Vision Laboratories), Joe Lapp (webMethods Inc.), Ora Lassila (Nokia Research Center), Andrew Layman (Microsoft), Ralph LeVan (OCLC), John McCarthy (Lawrence Berkeley National Laboratory), Chris McConnell (Microsoft), Murray Maloney (Grif), Michael Mealling (Network Solutions), Norbert Mikula (DataChannel), Eric Miller (OCLC), Jim Miller (W3C, emeritus), Frank Olken (Lawrence Berkeley National Laboratory), Jean Paoli (Microsoft), Sri Raghavan (Digital/Compaq), Lisa Rein (webMethods Inc.), Paul Resnick (University of Michigan), Bill Roberts (KnowledgeCite), Tsuyoshi Sakata (Digital Vision Laboratories), Bob Schloss (IBM), Leon Shklar (Pencom Web Works), David Singer (IBM), Wei (William) Song (SISU), Neel Sundaresan (IBM), Ralph Swick (W3C), Naohiko Uramoto (IBM), Charles Wicksteed (Reuters Ltd.), Misha Wolf (Reuters Ltd.), Lauren Wood (SoftQuad).

11 References

Normative References

[RDF-MS]

Resource Description Framework (RDF) Model and Syntax Specification, O. Lassila and R. Swick, Editors. World Wide Web Consortium. 22 February 1999. This version is http://www.w3.org/TR/1999/REC-rdf-syntax-19990222. The latest version of RDF M&S is available at http://www.w3.org/TR/REC-rdf-syntax.

[XML]

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

[XML-NS]

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

[INFOSET]

XML Information Set, J. Cowan and R. Tobin, Editors. World Wide Web Consortium. 24 October 2001. This version is http://www.w3.org/TR/2001/REC-xml-infoset-20011024. The latest version of XML Information set is available at http://www.w3.org/TR/xml-infoset.

[URIS]

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

[RDF-CONCEPTS]

RDF Concepts and Abstract Syntax, G. Klyne, J. Carroll, Editors, World Wide Web Consortium W3C Working Draft, work in progress, 8 November 2002. This version of the RDF Concepts and Abstract Syntax is http://www.w3.org/TR/2002/WD-rdf-concepts-20021108/. The latest version of the RDF Concepts and Abstract Syntax is at http://www.w3.org/TR/rdf-concepts/.

[RDF-TESTS]

RDF Test Cases, J. Grant and D. Beckett, Editors. Work in progress. World Wide Web Consortium, 29 April 2002. This version of the RDF Test Cases is http://www.w3.org/TR/2002/WD-rdf-testcases-20020429/. The latest version of the RDF Test Cases is at http://www.w3.org/TR/rdf-testcases.

[KEYWORDS]

RFC 2119 - Key words for use in RFCs to Indicate Requirement Levels, S. Bradner, IETF. March 1997. This document is http://www.ietf.org/rfc/rfc2119.txt.

[RFC-3023]

RFC 3032 - XML Media Types, M. Murata, S. St.Laurent, D.Kohn, IETF. January 2001. This document is http://www.ietf.org/rfc/rfc3023.txt.

[RDF-MIMETYPE-ID]

application/rdf+xml Media Type Registration, Internet-Draft draft-w3c-rdfcore-rdfxml-mediatype-01, A. Swartz, 23 August 2002.

[XML-BASE]

XML Base, J. Marsh, Editor, W3C Recommendation. World Wide Web Consortium, 27 June 2001. This version of XML Base is http://www.w3.org/TR/2001/REC-xmlbase-20010627/. The latest version of XML Base is at http://www.w3.org/TR/xmlbase/.

Informational References

[CHARMOD]

Character Model for the World Wide Web 1.0, M. Dürst, F. Yergeau, R. Ishida, M. Wolf, A. Freytag, T Texin, Editors, World Wide Web Consortium Working Draft, work in progress, 20 February 2002. This version of the Character Model is http://www.w3.org/TR/2002/WD-charmod-20020220/. The latest version of the Character Model is at http://www.w3.org/TR/charmod/.

[RDF-SEMANTICS]

RDF Model Theory, P. Hayes, Editor. Work in progress. World Wide Web Consortium, 14 February 2002. This version of the RDF Semantics is http://www.w3.org/TR/2002/WD-rdf-mt-20020214. The latest version of the RDF Semantics is at http://www.w3.org/TR/rdf-mt/.

[RDF-PRIMER]

RDF Primer, F. Manola, E. Miller, Editors, World Wide Web Consortium W3C Working Draft, work in progress, 26 April 2002. This version of the RDF Primer is http://www.w3.org/TR/2002/WD-rdf-primer-20020426/. The latest version of the RDF Primer is at http://www.w3.org/TR/rdf-primer/.

[RDF-VOCABULARY]

RDF Vocabulary Description Language 1.0: RDF Schema, D. Brickley, R.V. Guha, Editors, World Wide Web Consortium W3C Working Draft, work in progress, 30 April 2002. This version of the RDF Vocabulary Description Language is http://www.w3.org/TR/2002/WD-rdf-schema-20020430/. The latest version of the RDF Vocabulary Description Language is at http://www.w3.org/TR/rdf-schema/.

STRIPEDRDF

RDF: Understanding the Striped RDF/XML Syntax, D. Brickley, W3C, 2001. This document is http://www.w3.org/2001/10/stripes/.

XPATH

XML Path Language (XPath) Version 1.0, J. Clark and S. DeRose, Editors. World Wide Web Consortium, 16 November 1999. This version of XPath is http://www.w3.org/TR/1999/REC-xpath-19991116. The latest version of XPath is at http://www.w3.org/TR/xpath.

SAX2

SAX Simple API for XML, version 2, D. Megginson, SourceForge, 5 May 2000. This document is http://sax.sourceforge.net/.

RSS

RDF Site Summary (RSS) 1.0, G. Beged-Dov, D. Brickley, R. Dornfest, I. Davis, L. Dodds, J. Eisenzopf, D. Galbraith, R.V. Guha, K. MacLeod, E. Miller, A. Swartz, E. van der Vlist, 2000. This document is http://purl.org/rss/1.0/spec.

CC/PP

Composite Capability/Preference Profiles (CC/PP): Structure and Vocabularies, G. Klyne, F. Reynolds, C. Woodrow, H. Ohto, World Wide Web Consortium Working Draft, work in progress, 15 March 2001. This version is http://www.w3.org/TR/2001/WD-CCPP-struct-vocab-20010315/. The latest version of CC/PP structure and Vocabularies is available at http://www.w3.org/TR/CCPP-struct-vocab.

UNPARSING

Unparsing RDF/XML, J. J. Carroll, HP Labs Technical Report, HPL-2001-294, 2001. This document is available at http://www.hpl.hp.com/techreports/2001/HPL-2001-294.html.

RELAXNG

RELAX NG Specification, James Clark and MURATA Makoto, Editors, OASIS Committee Specification, 3 December 2001. This version of RELAX NG is http://www.oasis-open.org/committees/relax-ng/spec-20011203.html. The latest version of the RELAX NG Specification is at http://www.oasis-open.org/committees/relax-ng/spec.html.

RELAXNG-COMPACT

RELAX NG Compact, James Clark, Editor. OASIS Working Draft, 7 June 2002. This document is http://www.oasis-open.org/committees/relax-ng/compact-20020607.html.

XML Schema Part 0: Primer

XML Schema Part 0: Primer - W3C Recommendation, World Wide Web Consortium, 2 May 2001.

XML Schema Part 1: Structures

XML Schema Part 1: Structures - W3C Recommendation, World Wide Web Consortium, 2 May 2001.

XML Schema Part 2: Datatypes

XML Schema Part 2: Datatypes - W3C Recommendation, World Wide Web Consortium, 2 May 2001.

Schematron

Schematron, Rick Jelliffe, Academia Sinica Computing Centre, Taibei.

[RDF-IN-XHTML]

RDF in HTML: Approaches, Sean B. Palmer, 2002

[RFC-2731]

RFC 2731 - Encoding Dublin Core Metadata in HTML, John Kunze, DCMI, December 1999.

Appendix A: Issues affecting RDF/XML Syntax (Informative)

This section records local issues to be resolved and issues that were reported to the RDF Core Working Group related to the XML syntax and their disposition. This section is not the definitive list or description of the latter - see the RDF Core Working Group issues list. Decided issues may also have associated test cases which can be found in the RDF Test Cases W3C Working Draft.

A.1: Document Issues / Tasks (Informative)

None.

A.2: RDF Core Working Group Open Issues affecting RDF/XML Syntax (Informative)

None.

A.3: RDF Core Working Group Decided Issues affecting RDF/XML Syntax (Informative)

rdfms-syntax-incomplete

The RDF/XML syntax can't represent an an arbritary graph structure.

On 26th July 2002, the WG decided to re-open this issue and accept the proposal (as amended) to add an rdf:nodeID to the syntax for specifying blank nodes in triple subject and object positions.

On 26th October 2001, the WG decided that this issue was postponed for consideration by a future Working Group.

Action: Added constraint constraint-nodeID (later removed) and Production nodeIdAttr, and amended productions syntaxTerms, nodeElement and emptyPropertyElt to take rdf:nodeID.

rdf-namespace-change

Should the rdf: and/or rdfs: namespace URI refs be changed?

On 17th June 2002, the RDFCore WG resolved to modify the existing RDF and RDFS namespaces rather than create new ones and seek implementor feedback on this decision.

Action: None needed.

rdfms-seq-representation

The ordinal property representation of containers does not support recursive processing of containers in languages such as Prolog.

On 31st May 2002 the WG resolved:

• Approve Jos's test case as the basis for resolving this issue
• Add the new names [rdf:List, rdf:first, rdf:rest and rdf:nil] to the rdf namespace
• use rdf:parseType="Collection"
• typed nodes are permitted as collection members

Action: Added 7.2.19 Production parseTypeCollectionPropertyElt, 7.2.31 Production parseCollection and updated 7.2.14 Production propertyElt to use this.

rdf-ns-prefix-confusion

On 25th May 2001, the WG decided that ALL attributes must be namespace qualified. There is a description of the decision, including detail on the grammar productions affected and a collection of test cases

Action: Removal of original grammar productions 6.6, 6.7, 6.8, 6.9, 6.11, 6.18, 6.32, 6.33

rdfms-duplicate-member-props

may a container have duplicate containerMembership properties?

On 3rd May 2002, the WG resolved:

<rdf:Bag rdf:about="http://example.org/foo">
  <rdf:_1 rdf:resource="http://example.org/a" />
  <rdf:_1 rdf:resource="http://example.org/b" />
</rdf:Bag>

is syntactically legal RDF.

Action: None needed.

rdfms-abouteachprefix

On 1st June 2001, the WG decided that aboutEachPrefix would be removed from the RDF Model and Syntax Recommendation on the grounds that there is a lack of implementation experience, and it therefore should not be in the recommendation. A future version of RDF may consider support for this feature.

Action: Removal of original grammar production 6.8

rdf-containers-syntax-ambiguity
rdf-containers-syntax-vs-schema

On 29th June 2001, the WG decided that containers will match the typed node production in the grammar (production 6.13) and that the container specific productions (productions 6.25 to 6.31) and any references to them be removed from the grammar. rdf:li elements will be translated to rdf:_nnn elements when they are found matching either a propertyElt (production 6.12) or a a typedNode (production 6.13). The decision includes a set of test cases.

Action: Removal of original grammar productions 6.25, 6.26, 6.27, 6.28, 6.29, 6.30, 6.31

rdfms-empty-property-elements

On 8th June 2001 the WG decided how empty property elements should be interpreted. The decision is fully represented by the test cases.

Action: Inserted pointers to the the test cases into the grammar at the places where empty property elements are recognized.

rdfms-aboutEach-on-object

On 29th June 2001, the WG decided that rdf:aboutEach attributes are not allowed on an rdf:Description (or typed node) element which is the object of a statement.

Action: None needed - rdf:aboutEach removed from the language on 7th December 2001.

rdfms-syntax-desc-clarity

The language describing the syntax is unclear [in section 6]

On 26th October 2001, the WG decided that this issue is closed by the new approach to defining the syntax in this document.

Action: A main goal of this document is to make the syntax clearer and more precise. In particular the grammar section and the pointers to schemas for XML validation help address this.

rdfms-formal-grammar

A formal grammar for RDF.

On 26th October 2001, the WG decided that this issue is closed by the new approach to defining the syntax in this document.

Action: A main goal of this document is to make the syntax clearer and more precise. In particular the grammar section and the pointers to schemas for XML validation help address this.

rdfms-validating-embedded-rdf

On 9th November 2001, the RDFCore WG resolved to postpone the issue "for later consideration on the grounds that it is out of scope of its current charter to change the current RDF/XML syntax to the extent necessary to address it."

Action: None needed.

rdfms-rdf-names-use

On 30th November 2001, the WG decided that this issue was closed by the following resolution.

The use of rdf:RDF, rdf:ID, rdf:about, rdf:resource, rdf:bagID, rdf:parseType, rdf:aboutEach and rdf:li except as reserved names as specified in the grammar is an error. [Later rdf:aboutEach was removed from the language on 7th December 2001]

On 25th February 2002, the WG further resolved that:.

The WG reaffirmed its decision not to restrict names in the RDF namespaces which are not syntactic. The WG decided that an RDF processor SHOULD emit a warning when encountering names in the RDF namespace which are not defined, but should otherwise behave normally.

Action: Added note to section 5.1 RDF Namespace

rdfms-abouteach

processing rdf:aboutEach requires a processing of sub-property relations.

On 7th December 2001, the WG resolved to remove rdf:aboutEach from the language.

Action: Removed from the grammar.

rdfms-propElt-id-with-dr

On 7th December 2001, the WG decided to remove rdf:aboutEach from the language and consequently this issue was closed.

Action: None needed.

rdfms-difference-between-ID-and-about

What is the difference between using and ID attribute to 'create' a new resource and an about attribute to refer to it?

On 14th December 2001, the WG decided that this document resolves the issue.

Action: See section on Identifiers for details.

rdfms-qname-uri-mapping

On 11th January 2002, the WG resolved (revised) "to not change the algorithm for mapping qnames to uris and close this issue on the grounds":

1. Such a change would be a major change to the mapping of RDF/XML syntax to the model and would be beyond our charter.
2. It would cause the same RDF/XML to generate a different graph from existing versus revised implementations
3. Existing code may generate wrong (illegal) graphs for some RDF/XML.

Action: None needed.

rdfms-reification-required

On 11th January 2002, the WG resolved (revised) "that a parser is not required to create bags of reified statements for all rdf:Description elements, only those which are explicitly reified using an rdf:ID on a propertyElt or by an rdf:bagID on the rdf:Description.

Existing test cases such as rdf-ns-prefix-confusion test0001 (test0001.rdf, test0001.nt) demonstrate this resolution."

Action: None needed - matches the existing syntax description.

rdfms-replace-value

On 11th January 2002, the WG resolved (revised) "to not change the name of this property at this time on the grounds:

• insufficient reasons to make this change
• will cause existing uses to be illegal - such as examples in M&S.

and resolves to recast the issue as a need to clarify the semantics of rdf:value."

At the February 2002 face to face meeting, the RDFCore WG resolved:

• that rdf:value is a property defined in the RDF namespace
• that the model theory state that rdf:value is a property
• that no other model theory semantics is defined specifically for it
• the issue be closed.

Action: None needed.

mime-types-for-rdf-docs

On 18th January 2002, the WG authorized the removal of this issue from this document by the adding a new section with the wording proposed now included in the RDF MIME type section.

When the WG is ready (documents are stable), the MIME content-type registration for application/rdf+xml will proceed.

Action: Added RDF MIME type section.

rdfms-xml-base

On 18th January 2002, the WG decided that "xml:base be allowed, and honored, anywhere in an RDF document".

On 25th February 2002, the WG decided (1) that xml:base applies to RDF's use of document references (fragments)
(2) that xml:base hierarchical URIs without a path component shall have it set to /.
(3) the scope of xml:base attributes should be taken into account when checking for duplicate rdf:ID values

Action: Added details in Section 6 Data Model near introduction of Infoset and added new Section 5.3 Base URIs

rdfms-nested-bagIDs

What triples are generated for nested description elements with bagIDs?

On 25th February 2002, the WG decided that this issue was closed by the following resolution.

A bagID reifies the property attributes on the same element as the bagid, the type node and statements immediately arising from property elements that are immediate children of the element containing the bagId. In particular a property element whose statement is part of the bag, which has property attributes, those statements are not part of the bag.

Action: bagID algorithm added to nodeElement emptyPropertyElt.

rdfms-not-id-and-resource-attr

The propertyElt production 6.12 of the grammar does not allow both an ID attribute and a resource attribute to be specified.

On 25th February 2002, the WG decide that this issue was closed by making rdf:ID always specify the ID of the reified statement (parent node, property element, node).

Action: Updated 7.2.21 Production emptyPropertyElt and Relax NG schema to reflect decision.

rdfms-xmllang

Why isn't xml:lang information represented within the RDF data model?

On 25th February 2002, the WG decided that this issue was closed by the following resolution.

A literal consists of three components:

• A representation of the parseType, which is a single bit
• A language indicator which is a string as defined in XML
• A fully normalized UNICODE string.

Action: Added the language node term from the value of xml:lang attributes, added sections Plain Literal Node, and XML Literal Node and updated parseTypeOtherPropertyElt for parseType.

rdfms-xml-literal-namespaces

How should a parser process namespaces in a literal which is XML markup?

On 15th March 2002, the WG decided that this issue was closed by the following resolution.

• The exact form of the string value corresponding to any given XML Literal within RDF/XML is implementation dependent.
• the string value is well-balanced XML
• taking the exclusive canonicalization of both the original XML Literal in its containing document, and the string value of the literal produce the same character string. This will be used as the basis for test cases.
• The canonicalization above is without comments i.e. CONFORMANCE should be tested without comments; dropping comments was NOT mandatory.
• this issue is closed
• to raise a comment on the XQuery/XPath 2.0 data model that it does not adequately address the handling of namespace prefixes appearing in attribute values.

Action: Discussed in RDF Concepts and Abstract Syntax [RDF-CONCEPTS] Section 3 XML Literals and Section 5.1 Character normalization

rdf-charmod-literals

Does the treatment of literals conform to charmod ? [CHARMOD]

On 5th April 2002, the RDFCore WG resolved this issue by approving test cases white, black 1 and black 2 submitted for consideration. The grey test cases were not approved; instead the WG decided to add text to the syntax specification pointing out that literals beginning with a combining character may not be serializable in RDF/XML, depending on the outcome of [CHARMOD], and may cause interoperability problems.

Action: Notes added: 1, 2
Discussed in RDF Concepts and Abstract Syntax [RDF-CONCEPTS] Section 4.1 Character normalization

rdf-charmod-uris

Does the treatment of uri-references conform with charmod? [CHARMOD]

On 26th April 2002, the WG decided to:

Action: leave URI references as un-escaped Unicode

and approved test cases, later moved into the rdf-charmod-literals test cases area.

A.4: RDF Core Working Group Postponed Issues affecting RDF/XML Syntax (Informative)

rdfms-quoting

The syntax needs a more convenient way to express the reification of a statement.

On 26th October 2001, the WG decided that this issue was postponed for consideration by a future Working Group.

Action: None needed.

rdfms-qnames-cant-represent-all-uris

The RDF XML syntax cannot represent all possible Property URI's.

On 26th October 2001, the WG decided that this issue was postponed for consideration by a future Working Group.

Action: None needed.

rdfms-qnames-as-attrib-values

Suggestion that Qnames should be allowed as values for attributes such as rdf:about.

On 26th October 2001, the WG decided that this issue was postponed for consideration by a future Working Group.

Action: None needed.

B Syntax Schemas (Informative)

Two schema language authors submitted schemas for RDF/XML based on the revised grammar in the previous version of this draft. We include pointers to these schemas for information purposes and an example schema; they are not part of this specification.

B.1 RELAX NG Compact Schema (Informative)

This is an example schema in RELAX NG Compact (for ease of reading) but applications can also use the RELAX NG XML version. These formats are described in RELAX NG ([RELAXNG]) and RELAX NG Compact ([RELAXNG-COMPACT]).

#
# RELAX NG Compact Schema for RDF/XML Syntax
#
# This schema is for information only and NON-NORMATIVE
#
# It is based on one originally written by James Clark in
# http://lists.w3.org/Archives/Public/www-rdf-comments/2001JulSep/0248.html
# and updated with later changes.
#

namespace local = ""
namespace rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"


start = doc


# I cannot seem to do this in RNGC so they are expanded in-line

# coreSyntaxTerms = rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType | rdf:resource | rdf:nodeID | rdf:datatype
# syntaxTerms = coreSyntaxTerms | rdf:Description | rdf:li
# oldTerms    = rdf:aboutEach | rdf:aboutEachPrefix
# nodeElementURIs       = * - ( coreSyntaxTerms | rdf:li | oldTerms )
# propertyElementURIs   = * - ( coreSyntaxTerms | rdf:Description | oldTerms )
# propertyAttributeURIs = * - ( coreSyntaxTerms | rdf:Description | rdf:li | oldTerms )


doc = 
  RDF

RDF =
  element rdf:RDF { nodeElementList }

nodeElementList = 
  nodeElement*

  # Should be something like:
  #  ws* , (  nodeElement , ws* )*
  # but RELAXNG does this by default, ignoring whitespace separating tags.

nodeElement =
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:aboutEach | rdf:aboutEachPrefix ) {
      (idAttr | nodeIdAttr | aboutAttr )?, bagIdAttr?, propertyAttr*, propertyEltList
  }

  # It is not possible to say "and not things
  # beginning with _ in the rdf: namespace" in RELAX NG.

ws = 
  " "

  # Not used in this RELAX NG schema; but should be any legal XML
  # whitespace defined by http://www.w3.org/TR/2000/REC-xml-20001006#NT-S


propertyEltList = 
  propertyElt*

  # Should be something like:
  #  ws* , ( propertyElt , ws* )*
  # but RELAXNG does this by default, ignoring whitespace separating tags.

propertyElt = 
  resourcePropertyElt | 
  literalPropertyElt | 
  parseTypeLiteralPropertyElt |
  parseTypeResourcePropertyElt |
  parseTypeCollectionPropertyElt |
  parseTypeOtherPropertyElt |
  emptyPropertyElt

resourcePropertyElt = 
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      idAttr?, nodeElement
  }

literalPropertyElt =
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      idAttr?, text 
  }

parseTypeLiteralPropertyElt = 
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      idAttr?, parseLiteral, literal 
  }

parseTypeResourcePropertyElt = 
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      idAttr?, parseResource, propertyEltList
  }

parseTypeCollectionPropertyElt = 
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      idAttr?, parseCollection, nodeElementList
  }

parseTypeOtherPropertyElt = 
  element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      idAttr?, parseOther, any
  }

emptyPropertyElt =
   element * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                 rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                 rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
       idAttr?, (resourceAttr | nodeIdAttr)?, bagIdAttr?, propertyAttr* 
   }

idAttr = 
  attribute rdf:ID { 
      IDsymbol 
  }

nodeIdAttr = 
  attribute rdf:nodeID { 
      IDsymbol 
  }

aboutAttr = 
  attribute rdf:about { 
      URI-reference 
  }

bagIdAttr = 
  attribute rdf:bagID {
      IDsymbol
  }

propertyAttr = 
  attribute * - ( rdf:RDF | rdf:ID | rdf:about | rdf:bagID | rdf:parseType |
                  rdf:resource | rdf:nodeID | rdf:datatype | rdf:li |
                  rdf:Description | rdf:aboutEach | rdf:aboutEachPrefix ) {
      string
  }

resourceAttr = 
  attribute rdf:resource {
      URI-reference 
  }

datatypeAttr = 
  attribute rdf:datatype {
      URI-reference 
  }

parseLiteral = 
  attribute rdf:parseType {
      "Literal" 
  }

parseResource = 
  attribute rdf:parseType {
      "Resource"
  }

parseResource = 
  attribute rdf:parseType {
      "Collection"
  }

parseOther = 
  attribute rdf:parseType {
      text
  }

URI-reference = 
  string

literal =
  any

IDsymbol = 
  xsd:NMTOKEN

any =
  mixed { element * { attribute * { text }*, any }* }

B.2 Other Syntax Schemas (Informative)

Two schema language authors submitted schemas for RDF/XML based on the new grammar in previous versions of this draft. The pointers to these schemas are included here for information purposes only; they are not part of this specification.

• Relax NG Compact schema by James Clark - see [RELAXNG] and section B.1
• Schematron schema by Rick Jellife - see [Schematron]
• XML Schema by the editor of this spec (not working yet) - see [XML Schema Part 0: Primer], [XML Schema Part 1: Structures] and [XML Schema Part 2: Datatypes].

C Changes (Informative)

Changes since the 25 March 2002 working draft

(Newest at top)

• Added warning in B.1 RELAX NG compact schema - this schema is untested
• Added note to Section 2 that in case of conflict, grammar sections rule
• Added oldTerms to forbid aboutEach, aboutEachPrefix
• RDF Model Theory now RDF Semantics
• Terminology consistency - URIs now RDF URI References, Blank Nodes and Blank Node Identifiers, Plain Literals, Nodes are RDF URI References etc, Arcs are labeled with RDF URI References, XML Literals, all linking [RDF-CONCEPTS]
• Many rewordings in new Section 2 and elsewhere after WG review comments
• Added Section 2 sub-sections to table of contents
• Cut down Section 8 Serializing an RDF Graph to RDF/XML now that rdf:nodeID allows many more graphs to be serialized.
• Update for N-Triples syntax for datatype literals: "foo"@en^^<datatypeURI>
• Massive update to Section 2 - An XML syntax for RDF - added examples to cover hopefully all of RDF/XML
• Added lots of pointers to RDF Concepts and Abstract Syntax working draft
• Added rdf:datatype to the syntax
• Issue rdfms-duplicate-member-props closed - no action needed.
• Issue rdfms-seq-representation closed
  Added rdf:parseType="Collection" to the syntax.
  Added parseTypeCollectionPropertyElt, parseCollection to grammar and updated propertyElt.
• Issue rdf-namespace-change closed - no action needed.
• Reordered the document structure. 3 to 6, 3.1 to 6.1, 3.2 to 6.2, 3.3 to 4, 3.4 to 5.1, 3.5 to 5.2, 3.6 to 5.4, 3.7 to 5.3, 4 --, 4.1 to 3, 4.2 to 6.3, 5 to 7, 5.0 to 7.1, 5.1..5.25 to 7.2.x, 5.26 to 7.3, 5.27 to 7.4, 5.28 to 7.5, 5.29 to 7.6, X to 8, 6 to 9, 7 to 10, 8 to 11
• Issue rdfms-syntax-incomplete (reopened, updated)
  Added rdf:nodeID attribute and constraint-nodeID (later removed).
  Updated nodeElement, emptyPropertyElt grammar terms.
  Added nodeIdAttr.
• Issue faq-html-compliance closed
  Added Section 9 Using RDF/XML with HTML and XHTML
• Section 6.3 Notation
  Split into general, matching and action notations.
  Renamed start_element to start-element and end_element to end-element.
  Changed notation of equality to == and assignment to :=
• Many rewordings and changes after extensive feedback from Bijan Parsia.
• Issue rdfms-seq-representation closed
  Section 5.1 RDF Namespace - Added rdf:List, rdf:first, rdf:rest, rdf:nil
• Renamed Nodes throughout with Events.
• Updated after comments by Brickley, 2002-03-24 Replaced model with graph throughout.
  Section 8 Serializing Updated to reword the introduction and added a note that information is lost when blank nodes are labeled with URI-refs.
• Update after comments by Patel-Schneider, 2002-05-21 outlined in response 1 and response 2.
  nodeElement - moved "if e.subject is empty" point to after rdf:ID and rdf:about processing.
  Section 5.4 Constraints - added and moved the rdf:ID and rdf:bagID constraints there linked from the old location in the grammar.
  Section 2 Updates on abbreviation of properties into XML attributes
• Section 6 Serializing Changed "not used" to "no mapping" for other infoitem types.
• Changed data model 'property'/'properties' to 'accessor'/'accessors'
• Issue rdf-charmod-literals closed
  Added note 1 and node 2 near literal event descriptions.
• Section 6 Serializing Ensure spliting a URI results in a legal XML name; it must start with a letter or _ following XML's Name production.
• Section 6.1.7, Section 6.1.8: Added note 1, note 2 warning about literals beginning with combining chars
• Issue rdfms-xmllang closed.
  Added the language node term from the value of xml:lang attributes.
  Added sections Plain Literal Node, and XML Literal Node and updated parseTypeOtherPropertyElt for rdf:parseType.

Changes since the 18 December 2001 working draft

(Newest at top)

• Updated status and abstract for this WD
• Updated table of contents to include substructure of section 7
• Require that URIs MUST NOT be generated for blank identifiers
• Specify syntax/non-syntax parts of RDF namespace
• Use RDF Graph rather than RDF Model throughout
• Sections Plain Literal Node, and XML Literal Node that N-Triple string escape rules are required when generating N-Triple strings
• Remove xml* attributes that are not used (we use xml:lang, Infoset uses xml:base)
• Added references to RDF Primer [RDF-PRIMER] working draft
• Section 2: Added more examples to illustrate some (not all) syntax abbreviations
• Added xml:lang support by adding a new element property, using it throughout to generate literal() or xml() literals
• Added a grammar summary section (experimental)
• Added an explicit constraint on rdf:ID and rdf:bagID values, and with respect to the base URI
• Updated notation for A:=B assignment, string literal and xml literals
• Removed note on propertyElt about potential future parseTypes values
• Correct the illegal rdf:* names on node and property elements
• List all infoitems indicating ones that are not used; and note that all infoitems must be preserved inside parseTypeLiteral
• In rdf-id production, kept rdf:ID as XML Nmtoken
• Added style from XSD for term definition and reference
• Introduction gained pictures taken from draft primer
• Added Nodes for all SAX-like nodes
• Added rdf:bagID rules in nodeElement and emptyPropertyElt
• Added Section 5.3 Base URIs for XML Base support, updated other sections and added to references
• emptyPropertyElt: Allow rdf:ID and rdf:resource together; updated Relax NG schema to match
• Section 5.1: Noted unknown rdf: names generate a warning
• Section 5.3: Made parseType only take "Resource", "Literal" and other values are always the same as "Literal"
• Added Section 4 RDF MIME Type to note proposed mime type
• Updated issues list to record closed and postponed issues
• Removed original grammar (Appendix C), updated grammar (Appendix D) sections

Changes since the 06 September 2001 working draft

• Most of the document is new
• Original document grammar sections moved to appendices
• Expressed in more detail the use of the XML Infoset as used here in a SAX-like manner
• Grammar updated to remove rdf:aboutEach - see rdfms-abouteach for details.
• Added the mapping to the RDF Model as expressed by N-Triples
• Added the non-normative RELAX NG schema
• Added Issue sections
• Added serialization section
• Added introduction to the RDF/XML syntax