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Created: March 26, 2002.
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W3C Updates RDF/XML Syntax Specification.

The W3C RDF Core Working Group has published a working draft for RDF/XML Syntax Specification (Revised). The revised draft supersedes the previous W3C RDF Model & Syntax specification published 1999-02-22. The new WD is issued in response to "the need for a number of fixes, clarifications, and improvements to the specification of RDF's abstract graph and XML syntax. Implementations of the earlier syntax and comparison of the resulting RDF graphs had shown that there was ambiguity; implementations generated different graphs and certain syntax forms were not widely implemented." The new RDF/XML syntax has been updated "to be specified in terms of the XML Information Set with new support for XML Base. For each part of the syntax, it defines the mapping rules for generating the RDF graph as defined in the RDF Model Theory. This is done using the N-Triples graph serializing test format which enables more precise recording of the mapping in a machine processable and testable form. These tests are gathered and published in the RDF Test Cases... the document re-represents the original EBNF grammar in terms of the XML Information Set items which moves from the rather low-level details, 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."

Bibliographic information: RDF/XML Syntax Specification (Revised). W3C Working Draft 25-March-2002. Version URL: Latest version URL: Previous version URL: Edited by Dave Beckett (University of Bristol).

From Dave Beckett's posting: the main changes in this version are:

  • The document handles the majority of the syntax in RDF M&S and the graph generation rules are considered mostly complete.
  • The completion of the rules for generating the graph for rdf:bagID
  • Rules for handling xml:lang with literals added.
  • Rules for handling XML Literals (not yet complete) from rdf:parseType="Literal".
  • The addition of XML Base support.
  • An updated introduction with new examples.

Appendix B presents (non-normative) Syntax Schemas for RDF/XML, including (1) Non-XML Relax NG schema (by James Clark), (2) Schematron schema (by Rick Jellife), and (3) W3C XML Schema (editors). These schemas are not an official part of the specification.

Mapping from the XML syntax to the RDF graph: "The mapping to the RDF graph is done by emitting statements in the form defined in the N-Triples section of RDF Test Cases Working Draft which creates an RDF graph, that has semantics defined by RDF Model Theory Working Draft. The document illustrates one way to create the N-Triples from the XML -- any other method that results in the same N-Triples (RDF graph) may be used. In particular: (1) The N-Triples may be generated in any order; (2) Duplicates may be eliminated at any point; (3) There is no requirement to support N-Triples in any way..."

Syntax summary: "The RDF Model Theory provides a formal description of RDF. This can be thought of as a graph consisting of nodes and arcs. The nodes can be labeled with URIs, literals or are blank and denote resources. The arcs connect the nodes and are all labeled with URIs. This graph is more precisely called a directed edge-labeled graph; each edge is an arc with a direction (an arrow) connecting two nodes. These edges can be described as triples of subject node, at the blunt end of the arrow/arc, property arc and an object node at the sharp end of the arrow/arc. The property arc can also be also interpreted as either a relationship between two resources or as defining an attribute value (object node) for some resource subject node. . In order to encode the graph in XML, the nodes and arcs are turned into XML elements, attributes, element content and attribute values. The URI labels for properties and object nodes are written in XML via XML Namespaces which gives a namespace URI for a short prefix along with namespace-qualified elements and attributes names called local names. The (namespace URI, local name) pair are chosen such that concatenating them forms the original node URI. The URIs labeling subject and object nodes are stored in XML attribute values. The nodes labeled by string literals (which are always object nodes) become element text content or attribute values..."

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