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RE: Expressiveness of RDF as Rule Conclusion Language (KIF or not to KIF)

From: Wagner, G.R. <G.R.Wagner@tm.tue.nl>
Date: Tue, 16 Oct 2001 16:04:05 +0200
Message-ID: <511BB18E82E9D11188230008C724064602D9DE22@tmex1.tm.tue.nl>
To: "'Pat Hayes'" <phayes@ai.uwf.edu>
Cc: "'www-rdf-rules@w3.org '" <www-rdf-rules@w3.org>
> >    [Gerd Wagner]
> >    Notice that we can associate a model-theoretic semantics with 
> >    rules in a natural way: an interpretation satisfies a rule 
> >    (is a model of it) if it satisfies its consequent whenever it 
> >    satisfies its antecedcent. 
> >    ... using the above definition of a model of a rule, we can 
> >    define that a rule set R entails a sentence F
> >    if all models of R satisfy F.

> >    [Pat Hayes] 
> >    However, that is not the way that the KIF authors are intending
> >    to use the term 'rule'
> >
> >But then they have a somewhat strange understanding of rules.
> 
> It evidently does not correspond to yours. It is, however, one that 
> has a long tradition in some academic circles, and to which the KIF 
> authors were referring.
> ...
> I do not have either the time nor the inclination to argue this case 
> with you, as there is really nothing useful to argue about. The point 
> at issue is that there is a sense of 'rule' which was being used by 
> the KIF authors that does not correspond to your understanding. That 
> does not mean that they were making a mistake, however.

You seem to suggest that he above model-theoretic characterisation 
of rules is just my private opinion, and that it is no problem (e.g. 
for KIF) to ignore it. This is not the case! Such a model-theoretic 
treatment of rules is kind of folkloristic and also used in logic 
text books.

> >You may intend them to be used in an
> >incomplete inference operation, but as I have argued above,
> >why would you want that we miss certain valid conclusions
> >that could be drawn if we just 'repair' the inference engine?
> 
> Maybe it was never broken. 

If you say "broken" then you should be able to tell me with 
respect to what semantics? Or do you identify the semantics 
with the particular inference engine chosen here?

> >So, apparently, KIF wants to stay at the "safe"
> >side (classical logic) while at the same time it wants to use
> >a negation that is more intuitive and cognitively adequate than
> >classical negation. But such a balancing act is not possible!
> 
> Seems easy enough to me. Use two negations, for example.

That's exactly what we have in (extended) logic programs.
But it's no longer classical logic!

-Gerd


---------------------------------------
Gerd Wagner  
http://tmitwww.tm.tue.nl/staff/gwagner/
Dep. Information & Technology 
Eindhoven University of Technology  
Email: G.Wagner@tm.tue.nl 
Phone: (+31 40) 247 26 17  
Fax: (+31 40) 247 26 12
Received on Tuesday, 16 October 2001 10:04:08 GMT

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