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Re: range, domain: Conjunctive AND disjunctive semantics both supportable

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Mon, 2 Oct 2000 15:26:44 +0100 (BST)
To: Graham Klyne <GK@dial.pipex.com>
cc: Ian Horrocks <horrocks@cs.man.ac.uk>, rdf interest <www-rdf-interest@w3.org>
Message-ID: <Pine.GHP.4.21.0010021516540.15453-100000@mail.ilrt.bris.ac.uk>
On Mon, 2 Oct 2000, Graham Klyne wrote:

> Ian,
> 
> I think what you describe has exactly the same effect as Jan Grant's recent 
> suggestion:
> 
> >and loosely:
> >
> >P has a range of (a member of the union of A and B)
> >
> >         A --[rdfs:subclassOf]-> anon:C
> >         B --[rdfs:subclassOf]-> anon:C
> >         P --[rdfs:range]-> anon:C
> >
> >(give anon:C a real URI if you prefer).
> 
> except that Jan's approach doesn't depend on additional 
> application-specific awareness.  Or am I missing something?

As has been pointed out, my construction gives you exactly what the
proposed disjunctive interpretation gives you, ie. not a lot! - unless
your application allows you to make further constraints.

What I would like to see is a general mechanism for expressing more
complex constraints within RDF. Some of the proposals we've seen in this
debate (and prior to it) are such useful mechanisms. The next question
to ask is "do they all belong in RDFS?" or is there room for a rdfs,
rdfc(onstraint) and rdfl(ogic) layer?

My only concern (hence my use of the slightly perjorative word
"burden") is that while having a standard mechanism for expressing
general constraints can only be a good thing, I think mandating such a
mechanism at too low a level in the RDF family of specs needs to be
considered carefully. Many people have application-specific semantics
which are useful, but might not paint the only picture. The trick is to
(a) get a general consensus as to what the commonalities of the various
techniques are, and (b) look at (possibly) breaking out the semantics
into a few layers with more general to more specific application. That
way we can hopefully maximise the benefit from the not inconsiderable
intellectual effort that folks are putting into this!

Just MHO, of course :-)

jan

-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287163 Fax +44 (0)117 9287112 RFC822 jan.grant@bris.ac.uk
Whose kung-fu is the best?
Received on Monday, 2 October 2000 10:26:50 GMT

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