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

Re: URI for language identifiers

From: Jan Algermissen <algermissen@acm.org>
Date: Tue, 01 Apr 2003 10:50:26 +0200
Message-ID: <3E8952D2.401B8DB4@acm.org>
To: Patrick.Stickler@nokia.com
CC: sandro@w3.org, dieter.koehler@philo.de, www-rdf-interest@w3.org


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.

Oh, but assuming that I understand the semantics of the foo namespace,
I could - yes?
Example: If the predicate is from Dublin Core, the subject is allways
the webpage, never an abstract concept.

I know, that is not RDF-ish thinking ;-)

> 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 ;-)

Huh...does that mean that 'proper' use or RDF does not allow me to use
addresses of existing web pages to refer to abstract concepts? That seems
like a severe limitation to me? Of what use is an identifier if I cannot
use for example HTTP GET to 'see/read' what it means?

Anyway, thanks Patrick, your reply is helping me a lot to understand
RDF (I think).
> > > (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. 

But this means disconnecting the idea of URIs from HTTP, right? URIs are
then only unambigous names and not 'Web Addresses; any more. I that true?

> No, that doesn't mean that that is
> always case. 

> Ambiguity and bugs are part of real life on the SW. 

<rant>Are you sure that is a solid foundation to stand on?</rant>

> 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,

No, in TM land, a URI allways is the address of 'the web page', a URI
*never* addresses an abstract concept.

Then in TMs URIs can be used as subject indicators, refering to
arbitrary subjects. A key concept is that when the URI of a subject indicator
is dereferenced and the retrieved information resource is rendered for human 
perception it should be clear what subject the URI indicates. 

> 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 couldn't you just make up a namespace that provides the predicates to
make scoping statements about 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

Jan Algermissen                           http://www.topicmapping.com
Consultant & Programmer	                  http://www.gooseworks.org
Received on Tuesday, 1 April 2003 03:48:29 UTC

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