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RE: rdfs:isDefinedBy (Was Re: Representing DCMI semantics as RDF schemas versus Web pages)

From: Bill de hÓra <dehora@eircom.net>
Date: Wed, 5 Jun 2002 12:39:23 +0100
To: "'RDF Interest'" <www-rdf-interest@w3.org>
Message-ID: <000a01c20c85$a493d290$887ba8c0@mitchum>

Hash: SHA1

> -----Original Message-----
> From: www-rdf-interest-request@w3.org 
> [mailto:www-rdf-interest-request@w3.org] On Behalf Of Patrick
> Stickler 
> The key requirement here is to be able to access knowledge 
> about a resource based on the URI of the resource. I.e., I 
> encounter some term and need to find out what it means.
> Well, there is no way to get from the URI to the namespace 
> based on the URI itself -- both because URIs are opaque to 
> RDF semantics and also because the partition between 
> namespace prefix and local name is lost and not reliably
> retrievable.  
> So, sticking some RDF schema on a server under the namespace 
> URL won't work anyway.

No, it'll work, this is the web after all. It just won't be implied
by RDF. We can bang on about the semantics of XML namespaces with
respect to RDF, but  people will go out and get things to work in
an ad-hoc case by case fashion a la RDDL. 

> But there is *no* reliable way to get from a URI to a 
> namespace, and hence namespace document or schema.

That's just hopelessly narrow. The reliable way occurs if people
agree to do so by sharing software that does it. If that's
perceived to be more valuable that a consistent interpretation of
URI refs, do not expect people to sit on their hands waiting for
RDF to come up with a solution. 

> Until a global knowledge base exists, folks should expect to 
> have to hand-feed their systems with schemas as required. At 
> least insofar as bootstrapping knowledge is concerned.

See above.

> No thanks. I'd rather have all of my SW applications agree on 
> what a given URI mean, rather than different applications 
> assigning different meaning.

Well that's cast in stone by the MT as I understand it. URI ref
meanings are fixed in the sense that their interpretation is fixed.
Whether anyone pays a blind bit of heed to it is another matter.

> Well, there's no problem with RDF applications locating
> and assimilating additional knowledge based on existing 
> statements, in fact, that's where alot of the really 
> interesting stuff happens.
> It's a matter of *how* the resources containing that 
> information are identified and the architectural mechanisms
> employed.  
> The present "hack" of guessing the namespace of some term,
> and trying to dereference some resource stored at the
> namespace URI is inherently broken. It is not supported
> by the existing web archtecture, nor by the RDF MT,
> nor by any formal representation of namespaces or their 
> relationship to terms in the graph.
> Making it work is all smoke and mirrors. It's a house
> of cards design and we're in for trouble if folks
> fail to come to grips with the fact that it's broken
> and incomplete.

If people really want to do this, smoke and mirrors will win out,
make no mistake. I don't care to define broken as not being
supported by web architecture (no doubt the TAG will tell what that
is someday) or not being in the MT or XML namespaces. The hack as
you call it (and why exactly do I have to hack? surely that's the
interesting question) is going to be done one way or another, cf
RDDL. Ultimately, whether it's by a HTTP GET or a mapping config
file or a batch load of assertions doesn't matter.

Bill de hÓra

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Received on Wednesday, 5 June 2002 07:41:43 UTC

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