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Re: Summary and some analysis: New Semantics Initiative

From: patrick hayes <phayes@ai.uwf.edu>
Date: Fri, 14 Jun 2002 22:02:20 -0500
Message-Id: <p05111a1cb9305c9c86b4@[65.217.30.123]>
To: Dan Connolly <connolly@w3.org>
Cc: w3c-rdfcore-wg@w3.org

>On Fri, 2002-06-14 at 10:37, R.V.Guha wrote:
>>  As for not using the rule of the excluded middle, etc. --- This is a
>>  much bigger issue than axiomatic approaches vs model theoretic
>>  approaches. The current model theories, from webont & rdf, do assume
>>  the law of the excluded middle.
>
>WebOnt does, yes. But RDF's model theory doesn't have negation
>at all... but... hmm... I suppose it does say that every
>triple (and every graph) is either true or false in
>every interpretation. Hmmm... I wish you hadn't pointed
>that out; I wasn't worried about it before now. ;-)

OK, let me suggest that you worry less. As you say, RDF has no 
negation. OK, so take a 2-valued interpretation, and re-interpret it 
so that 'false' means something else, eg 'not known to be true' or 
'false or undefined' or whatever takes your fancy as long as it 
definitely does not overlap with 'true'. Since entailment refers to 
satisfaction, which refers to truth, and there is no negation, what 
we call the 'not-true' value for propositions isn't really germane to 
the MT at all. You could interpret RDF intuitionistically or like LCF 
(truthvalues are true and undefined)  and it would have exactly the 
same entailments.

Of course, this doesn't extend to anything that has even a smidgeon 
of negation in it, such as DAML or OWL. But if you stay strictly in 
RDF, nobody can force you to exclude your middle.

Pat
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Received on Friday, 14 June 2002 23:02:20 EDT

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