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

RE: URI for language identifiers

From: Kal Ahmed <kal@techquila.com>
Date: 25 Apr 2003 09:45:39 +0100
To: Patrick.Stickler@nokia.com
Cc: algermissen@acm.org, sandro@w3.org, dieter.koehler@philo.de, www-rdf-interest@w3.org
Message-Id: <1051260339.1216.20.camel@piggy.ontopia.u-net.com>

On Tue, 2003-04-01 at 07:36, Patrick.Stickler@nokia.com wrote:
> > ... 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.

Surely then one *could* use the XTM-defined URI as a language identifier
by asserting that you are using it as such in a particular class of
predicate ? I'm not advocating that you do that in this case though...

The work of the OASIS Published Subjects TC is of importance both to the
RDF and TM communities. With PSIs that clearly *are* addresses of
resources whose purpose is to *describe* a subject, the relationship
between a PSI URI and the subject represented becomes much clearer.

> 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.

I think that subject indicating URIs can be used in an RDF graph safely
enough if one creates the necessary vocabulary to do so. Surely it would
be enough to create a predicate "psi:described-by" and then use a blank
node in the RDF graph ?

Similarly, for those URIs which are used purely as identifiers (as many
subject indicator URIs are in topic map land at the moment), a predicate
si:indicates should do the trick.

> 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.
Aye, but the nice thing about RDF is that if you are missing a bit of
machinery you can just invent a new predicate to plug the gap ;-)

> 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.

Used with caution, yes. But as your example at the top of this message
shows, that is true for any identifier over which you do not have
complete control (unless you are Humpty-Dumpty ;-)


Received on Friday, 25 April 2003 04:51:54 UTC

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