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Saturday, March 22, 2008

W3C Last Call Working Draft: Cool URIs for the Semantic Web

W3C announced that members of the Semantic Web Education and Outreach
(SWEO) Interest Group have published the Last Call Working Draft for
"Cool URIs for the Semantic Web." The document is intended to become
a W3C Interest Group Note giving a tutorial explaining decisions of
the TAG for newcomers to Semantic Web technologies. It was initially
based on the DFKI Technical Memo TM-07-01 and was subsequently published
as a W3C Working Draft in December 2007; it was reviewed by the Technical
Architecture Group (TAG) and the Semantic Web Deployment Group (SWD).
The document is a practical guide for implementers of the RDF
specification. The title is inspired by Tim Berners-Lee's article "Cool
URIs don't change". It explains two approaches for RDF data hosted on
HTTP servers. Intended audiences are Web and ontology developers who
have to decide how to model their RDF URIs for use with HTTP. Applications
using non-HTTP URIs are not covered. The document is an informative guide
covering selected aspects of previously published, detailed technical
specifications. The Resource Description Framework (RDF) allows users
to describe both Web documents and concepts from the real world -- people,
organisations, topics, things -- in a computer-processable way. Publishing
such descriptions on the Web creates the Semantic Web. URIs (Uniform
Resource Identifiers) are very important, providing both the core of
the framework itself and the link between RDF and the Web. This document
presents guidelines for their effective use. It discusses two strategies,
called 303 URIs and hash URIs. It gives pointers to several Web sites
that use these solutions, and briefly discusses why several other
proposals have problems. It is important to understand that using URIs,
it is possible to identify both a thing (which exists outside of the web)
and a web document describing the thing. For example the person Alice
is described on her homepage. Bob may not like the look of the homepage,
but fancy the person Alice. So two URIs are needed, one for Alice, one
for the homepage or a RDF document describing Alice. The question is
where to draw the line between the case where either is possible and the
case where only descriptions are available. According to W3C guidelines
in "Architecture of the World Wide Web, Volume One," we have an Web
document (there called information resource) if all its essential
characteristics can be conveyed in a message. Examples are a Web page,
an image or a product catalog. The URI identifies both the entity and
indirectly the message that conveys the characteristics. In HTTP, a
status 200 response code should be sent when a Web document has been
accessed, a different setup is needed when publishing URIs that are
meant to identify entities.

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