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Re: semantics status of RDF(S)

From: pat hayes <phayes@ai.uwf.edu>
Date: Sun, 8 Apr 2001 14:20:46 -0500
Message-Id: <v04210100b6f59391e8ce@[204.214.21.213]>
To: jos.deroo.jd@belgium.agfa.com
Cc: aswartz@swartzfam.com, www-rdf-logic@w3.org
>[...]
> >Asserting a negation is more than simply not asserting the negated
> >proposition: it is DENYING it. So if RDF supported negation, then an
> >RDF processor should draw a conclusion from finding P and the
> >negation of P: it ought to notice that they are contradictory. The
> >central point, however, is that an RDF triple is supposed to assert
> >that a relation holds; and negation is not a relation. So if it is
> >encoded as an RDF relation, something needs to 'know' that this
> >particular usage isnt meant to be taken literally in RDF, but is
> >simply a usage of the RDF datamodel to encode something else. And
> >indeed RDF, like any other system of linked arcs which allows one to
> >build arbitrarily complex labelled graphs, can be used to encode (the
> >syntax of) other languages in this way. But that isnt using RDF to
> >express negation: it is using RDF datastructures to encode the syntax
> >of some other language which expresses negation.
>
>I'm used to think about ~p (negation of p) as p->false
>(the relation 'p implies false').
>So if we assert p->false (to be true) then p is false
>and if we found p->false to be false then p is true.

Correct.

>When using resolution one cannot have such p->false rules.

Incorrect. In fact, resolution REQUIRES the use of such clauses.

>So one cannot (as such) deny the fact that p is true.

Yes, one can. If one could not deny it, resolution could never find a 
contradiction.

>There is however an easier problem (maybe).
>On the proof level (where proof expressions live)
>we can discover that p has a no-proof-found value.
>Of course that is not the denial of p but that
>is not a problem for a proof expressions's life!
>All it has to express is evidence that can be
>syntactically checked to give semantic validity
>(and such expressions can contain p->false
>parts coming from negated premisses).

I have no idea what you are talking about in the above paragraph. Can 
you rephrase it? In particular, what is the 'proof level' ?

Pat Hayes

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Received on Sunday, 8 April 2001 17:24:55 GMT

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