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Re: definition of domain

From: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
Date: Thu, 12 Oct 2000 16:14:29 +0200
Message-ID: <39E5C745.C0A3C209@bat710.univ-lyon1.fr>
To: Tom Van Eetvelde <tom.van_eetvelde@alcatel.be>
CC: ML RDF-interest <www-rdf-interest@w3c.org>
Tom Van Eetvelde wrote:
> Pierre-Antoine CHAMPIN wrote:
> > By the way, the example you propose :
> >
> > <rdfs:Class rdf:ID="Carnivore">
> >      <rdfs:subClassOf rdf:resource = "Animal"/>
> >      <s:eats rdf:resource="#Animal"/>
> > </rdfs:Class>
> >
> > is definitely wrong (IMHO) :
> > it would mean that the set of all carnivors (an abstract entity) eats itself !
> 
> Ho ho ho, hold your horses Pierre-Antoine! :-) 'Definitely wrong' is a matter of ontology! Indeed, carnivores can eat carnivores!

My mistake again :
I should have written :

  the set of all carnivors (an abstract entity) eats the set of animals

My remark was not applying to cannibalism :)
Only that there is a difference between 

  "carnivores eat animals" (as you wrote it above, with plural names)

and

  "Carnivore eats Animal" (with singular names, denoting sets of individals")

> I guess that you are afraid of the graphs: how do you know if you can propagate an arrow, attached to a
> subclass resource, to an instance of the class. This is easy: look at the definition of the arrow as
> resource. If you want to say something about the abstract entity 'carnivore' that you do not want to see
> reflected in every carnivore instance, then you have to define your arrow (property) having a domain equal
> to 'Class' or more specific: the class of which 'carnivore' is an instance. Another abstract entity in the
> model, but I believe that it is very rare to actually describe a class itself (as abstract entity) with
> properties not in the RDFS spec. So I don't see this as a burden.

Any schema built on top of RDFS, to extends its expression power (which is weak, as you mentioned) will define properties applying to classes or other properties.


I do not say what you propose is nonsense (sorry for the aggressive "definitely wrong" stuff ;-) but that it is not the best way to express it.
Sure some clever system may "guess" whether the property applies really to the class or to each instance of it, but this is a risky guess... and tends to make specifications misleading. IMHO again :)

Or do you consider classes more like prototypes ?

  Pierre-Antoine

-- 
Sometimes I think the surest sign that intelligent life exists elsewhere in the
universe is that none of it has tried to contact us.
(Bill Watterson -- Calvin & Hobbes)
Received on Thursday, 12 October 2000 10:15:51 GMT

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