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.
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/.
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:
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.
Editors Note:
This section has substantially changed in this version of the working
draft and although the substance is not expected to change, it is
likely that it will go substantial editorial revision.
The Working Group particularly invites feedback on this section.
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.
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:
This corresponds to the Node/Arc stripes:
- Node with RDF URI Reference
http://www.w3.org/TR/rdf-syntax-grammar
- Arc labeled with RDF URI Reference
http://example.org/terms/editor
- Node with no RDF URI Reference
- Arc labeled with RDF URI Reference
http://example.org/terms/homePage
- 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.
<rdf:Description>
<ex:editor>
<rdf:Description>
<ex:homePage>
<rdf:Description>
</rdf:Description>
</ex:homePage>
</rdf:Description>
</ex:editor>
</rdf:Description>
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:
