W3C home > Mailing lists > Public > www-rdf-interest@w3.org > April 2003

RE: URIs : How to find the ontologies behind them

From: <Patrick.Stickler@nokia.com>
Date: Thu, 10 Apr 2003 09:40:56 +0300
Message-ID: <A03E60B17132A84F9B4BB5EEDE57957B5FBB7C@trebe006.europe.nokia.com>
To: <pfps@research.bell-labs.com>, <Eli@SemanticWorld.Org>
Cc: <www-rdf-interest@w3.org>

> > I'm primarily interested in the 'when the SW gets going' 
> case (it's about
> > time we get it going, no? ;).  You seem to be saying that a 
> best practice
> > would be to put the OWL describing the resource in the 
> place that the URI of
> > the resource refers to.
> Not necessarily in that exact place.  However, most RDF URI 
> references have
> fragment identifiers, so it would be possible for example to place
> information about http://foo.ex/bar#bax in a document located at
> http://foo.ex/bar.  

Sorry. Unfortunately, no.

RDF fragment IDs do not work in exactly the same way as XML ID's.

You can describe the resource http://foo.ex/bar#bax in a dozen
different RDF/XML instances, none of which are http://foo.ex/bar.
And in all cases, you need not use rdf:ID ever. So even if
http://foo.ex/bar#bax is defined by http://foo.ex/bar, that
doesn't guaruntee that rdf:ID="bax" occurs anywhere in that
RDF/XML instance.

And there is no assertion that http://foo.ex/bar#bax relates to
a particular XML *element* in an RDF/XML instance having an
rdf:ID="bax" even if the parser will map such an rdf:ID value
to a URI based on an xml:base separated by '#'. rdf:ID is
not defined as an XML ID attribute.

And in fact, though there should only be one occurrence of a given
rdf:ID value for an xml:base scope, one can have descriptions using
both rdf:ID and rdf:about about the very same resource in the same
RDF/XML instance.

One should not think of URIrefs as working in RDF the same way
as they do in an HTML browser. They don't.

Thus, just as one cannot reliably get to a namespace document
from a URI, one cannot get to a definitive RDF/XML instance from
a URIref.

*** TAKE NOTE: URIrefs are *fully opaque* in an RDF graph and SW
*** agents operating on RDF expressed knowledge should not attempt
*** to parse URIrefs to infer any relationships between the resource
*** denoted by the URIref and any other resource that might share
*** some intersection of some character sequence with the URIref. 

The SW deals with RDF graphs, not RDF/XML instances, so
one should not be concerned with aspects of the XML serialization 
when requesting knowledge from a knowledge base. And looking
at URI vs. URIref or URI vs. namespace relations (neither of 
which can be reliably utilized) is the wrong way to go.

The SW architecture should provide for a standardized means by
which, given a URIref, one can inquire from the web authority
of the URIref (presuming there is one) for a description of 
the resource denoted by the URIref.

One can also inquire from various registries or other sources
for non-web-authoritative descriptions of the resource, allowing
for one to syndicate various views and opinions of the resource.

URIQA will provide for both.

> ... I think that the
> relationship between ontologies and URI references is many to 
> many (and
> many to many in interesting ways).



Patrick Stickler, Nokia/Finland, (+358 40) 801 9690, patrick.stickler@nokia.com
Received on Thursday, 10 April 2003 02:41:02 UTC

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