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RE: URI for language identifiers

From: <Patrick.Stickler@nokia.com>
Date: Tue, 1 Apr 2003 09:36:17 +0300
Message-ID: <1057787253.IAA22192@phantom.w3.org>
To: <algermissen@acm.org>, <sandro@w3.org>
Cc: <dieter.koehler@philo.de>, <www-rdf-interest@w3.org>


> ... Given the RDF statement
> 
> http://www.w3.org/Consortium/ http://foo/director "Tim Berners Lee"
> 
> doesn't 'http://www.w3.org/Consortium/' refer to the W3C itself?


You couldn't know that from the statement itself, in isolation.

If the property http://foo/director had an rdfs:domain defined such as

   http://foo/directory rdfs:range ex:Organization .

then one could be able to infer that http://www.w3.org/Consortium denoted
the organization rather than the web page, since one could then infer that

   http://www.w3.org/Consortium rdf:type ex:Organization .

But simply *using* the URI in a statement that presumes it denotes the
organization (without actually being sure it does) is very bad practice,
and does not in any way change the intended meaning of the URI.

If in fact, the owner of that URI asserts that

   http://www.w3.org/Consortium rdf:type ex:WebPage .

then using it as the subject of http://foo/director would be an error
(presuming that web pages don't have directors, of course ;-)

> > (I made a proposal that RDF URI-Refs should sometimes be seen as
> > subject indicators [4], but it was not accepted.  After trying to
> > implement my proposal I'm not so fond of it myself.)
> 
> I think that proposal was quite good. IMHO the question if a URI
> identifies a 'page' or an abstract concept is NOT part of the
> semantics of that particular URI but depends on the linking
> context (the context in whitch the URI is used as a reference).
> 
> But I never managed to get that idea across I think...

The idea that the context of usage affects the denotation of a URI 
is one of the key points of incompatability between the TM model and that
of RDF.

In RDF, a given URIref is expected to have a consistent interpretation,
no matter what context it occurs in. No, that doesn't mean that that is
always case. Ambiguity and bugs are part of real life on the SW. But 
consistent global meaning is the goal, and SW agents by default should
be able to presume that whenever they encounter a given URIref, it 
always means the same thing.

TMs, on the other hand, allow for variability in the meaning of URIs,
and are in that way at odds with RDF and IMO not fully nor safely
reconcilable with RDF graphs.

It's a pity, since there are alot of great ideas in the TM model. I
particularly envy TM scoping mechanisms and eagerly look forward to
the time that RDF has an analogous, and standardized, scoping mechanism
for statements.

But I agree with Sandro that TM URIs are not necessarily compatable with
RDF and they should be used with great caution in an RDF graph.

Cheers,

Patrick

--
Patrick Stickler, Nokia/Finland, (+358 40) 801 9690, patrick.stickler@nokia.com
 
Received on Tuesday, 1 April 2003 01:36:24 GMT

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