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Re: RDF MT: rdfs interpretations of subClassOf and subPropertyOf

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 20 Nov 2002 11:09:07 -0600
Message-Id: <p05111b06ba01712b454c@[10.0.100.86]>
To: Jeen Broekstra <jeen.broekstra@aidministrator.nl>
Cc: www-rdf-comments <www-rdf-comments@w3.org>

>This came up during a discussion on www-rdf-interest, and while I am
>not quite sure I read the logic right, it seems there is an oddness in
>the interpretation rules for subClassOf and subPropertyOf in the new
>draft of the RDF MT, which I would like clarified.
>
>From Section 3.3:
>
>  <x,y> is in IEXT(I(rdfs:subClassOf)) if and only if x and y are in IC
>  and ICEXT(x) is a subset of ICEXT(y)
>
>Now suppose we have an RDF model which contains a single triple
>definining a class:
>
>  <_:MyClass> <rdf:type> <rdfs:Class>
>
>Would not the above condition imply that from this triple we can deduce:
>
>  <_:MyClass> <rdfs:subClassOf> <rdfs:Class>
>
>(since MyClass and rdfs:Class are both in IC and ICEXT(MyClass) is the
>  empty set).

How do you know that ICEXT(I(MyClass)) is empty? It could be 
anything, given only what you have said in the first triple.

In fact there is, I believe, no way to formally ensure that any RDFS 
class has an empty extension, since there is no negation in RDFS. 
(The possibility of datatype contradictions might have been one way, 
but I blocked that by making ill-typed literals denote some arbitrary 
non-literal value. At least, I hope I did ;-)

>Analogously for the interpretation of subPropertyOf.
>
>Am I doing something wrong here, or is this valid, or is it a bug in the
>MT?

I believe that you have assumed a closed-world property which is not 
supported by the MT.

But if I have missed something, please get back to me quickly.

Pat Hayes

>
>Best regards,
>
>Jeen
>--
>jeen.broekstra@aidministrator.nl
>aidministrator nederland bv - http://www.aidministrator.nl/
>julianaplein 14b, 3817 cs amersfoort, the netherlands
>tel. +31-(0)33-4659987, fax. +31-(0)33-4659987


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Received on Wednesday, 20 November 2002 12:09:11 GMT

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