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Re: Technical change to the RDFS MT

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Thu, 19 Sep 2002 11:39:03 +0100
Message-Id: <>
To: pat hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org


I don't have any problem with the proposed change, but I'm a little puzzled 
by your explanation.

Looking at the words, I read "A rdfs:subClassOf B is true in I  if 
ICEXT(I(A)) is a subset of ICEXT(I(B))" to mean the second part implies the 
first.  Thus I don't recognize the possible concern that A's class 
extension being a subclass of B's class extension could allow A 
rdfs:subClassOf B to be false.


At 04:01 PM 9/18/02 -0500, pat hayes wrote:

>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)
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Graham Klyne
Received on Thursday, 19 September 2002 06:23:32 UTC

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