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Technical change to the RDFS MT

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 18 Sep 2002 16:01:04 -0500
Message-Id: <p05111b06b9ae9691db82@[65.217.30.172]>
To: w3c-rdfcore-wg@w3.org

Guys,

Recent attempts (in collaboration with Peter and Ian) to reconcile 
the RDF(S) MT with the emerging OWL MT have suggested that it would 
be good to make a technical alteration to the semantic conditions for 
RDFS. I think that this change will make no appreciable difference to 
RDFS itself (ie it will give the same RDFS entailments), but am 
soliciting comments on this change from the WG before deciding to do 
it.

We can illustrate the point by considering rdfs:subClassOf. Right 
now, we say that

A rdfs:subClassOf B

is true in I  if ICEXT(I(A)) is a subset of ICEXT(I(B)). Which seems 
kind of obvious; but the idea is to change this to read " ... is true 
in I IFF  ... " , i.e. make the semantic conditions *necessary and 
sufficient* for the truth of the triple.

The reason this doesnt make any appreciable difference to RDFS is 
that RDFS has no notion of negation, so it doesnt really matter if it 
treats something as false when its really true, which would be 
possible in the current MT: that is, you could (currently) have two 
classes and one class extension be a subset of the other, and still 
count rdfs:SubClassOf as being false in that interpretation. That 
wouldnt matter since that interpretation wouldnt satisfy any 
antecedents that might trigger a wierd conclusion, since it just 
fails to make something true. But when we go to OWL, there is 
something like a negation (owl:complementOf), and so now this 
possible mismatch between what is actually correct in the 
interpretation and what triples the interpretation makes true 
suddenly starts to matter, both ways round.

Similar changes need to be made to the conditions for 
rdfs:subPropertyOf and the domain and range conditions, for similar 
reasons.

Unless anyone objects, I plan to make this change in the next (and 
hopefully close-to-final) version. So object now or forever hold your 
piece. (To emphasize, this change makes the MT *more* conventional 
rather than less, ie this is the standard way to do it)

Pat
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Received on Wednesday, 18 September 2002 17:01:07 EDT

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