W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > June 2001

Re: Model-specific identity for anon resources, and its representation: A new issue?

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 22 Jun 2001 22:03:02 -0500
Message-Id: <v04210100b75969659061@[205.160.76.176]>
To: Sergey Melnik <melnik@db.stanford.edu>
Cc: w3c-rdfcore-wg@w3.org
>Aaron Swartz wrote:
> >
> > On Thursday, June 14, 2001, at 06:31  AM,
> > jos.deroo.jd@belgium.agfa.com wrote:
> >
> > > We can imagine that anounymous terms are identified 'by their content'
> >
> > I certainly hope not. At least, this is not the way I use
> > anonymous terms. I imagine anonymous terms being equivalent to
> > stating "a term with these properties" not "all terms with these
> > properties". If two people in a room call out that they're
> > thinking of something gray...
> >
> >         :Person1 :thinkingOf [ :color :Gray ] .
> >         :Person2 :thinkingOf [ :color :Gray ] .
> >
> > ... we cannot conclude that they are both thinking of elephants,
> > or at least of the same thing. One may be thinking of the New
> > York Times and the other of his office building.
> >
> > I think you are smushing prematurely.
> >
> > And the current XML still doesn't have a way to say:
> >
> >         _:a :property _:b .
> >         _:b :property _:a .
> >
> > nor
> >
> >         :x :property _:a .
> >         :y :property _:a .
> >
> > If anonymous nodes are part of the abstract syntax (which we
> > seem to have implicitly agreed upon through our acceptance on
> > N-Triples), then this is an issue.
>
>
>I don't agree that anonymous nodes should be part of the abstract
>syntax, and would suggest to consider this issue when cleaning up the
>model. I'm convinced that (sufficiently) uniquely generated resources
>serve the purpose better than "anonymous" resources (for instance, in
>the example above you really might want to know whether Person1 and
>Person2 are referring to the same unknown gray thing). Explicit
>existentially qualified variables are IMO out of scope of our work.

Logically, names and top-level existentially quantified variables are 
effectively identical. If they are not effectively identical in RDF, 
the difference must depend on some aspect of RDF that goes beyond the 
usual model theory. No objection to that, but I would like to know 
what that aspect is so that we have some chance of capturing it in a 
formal semantics.

The issue over whether Person1 and Person2 are the same person is 
really not to do with anonymity as such, but with equality 
(identity). If the language has some way to say that two different 
names denote the same entity, ie some way to say a = b, then this 
issue is relevant and needs to be got clear. If it doesn't have any 
way to say that, however, then there really isnt any point in 
haggling over this matter. It will make no real difference to the 
language, since any interpretation that satisfies a set of RDF 
assertions could be extended to a similar one with a unique names 
assumption that also satisfies it.

Pat Hayes

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Received on Monday, 25 June 2001 10:42:46 EDT

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