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

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 --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayesReceived on Sunday, 8 April 2001 17:24:55 GMT

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