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Re: Antwort: Re: Fwd: logics of RDF

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Fri, 15 Feb 2002 03:41:45 -0500
Message-Id: <p05101440b89278c92eff@[192.168.0.6]>
To: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>
Cc: webont <www-webont-wg@w3.org>
>"Peter F. Patel-Schneider" wrote:
>>
>>  Unfortunately, RDFS has precisely the class that prevents layering,
>>  rdfs:Class.  Modifying RDFS to a layered theory might help, but this would
>>  be a significant modification of RDFS, as much of the justification for
>>  RDFS is precisely that it has classes like rdfs:Class.
>
>I think your last sentence exactly points at the heart of at least 
>one of our problems with RDF: 
>
>"much of the justification for RDFS is precisely that it has classes 
>like rdfs:Class."
>
>I wonder if that is really true.

No, I think this is nonsense. If you delete the last two words I 
would agree with it.

>Yes, it is important for RDFS that we can form classes of classes 
>(and this feature is actively), but it is really necessary that 
>rdfs:Class is an instance of >*itself*< (ie breaking the layered 
>theory?)

I don't think it is centrally important. However it is kind of cute, 
and I don't think it in fact is a problem either semantically or 
syntactically.

>
>I would suggest that most (if not: all) of the usage of rdfs:Class 
>would still work within a layered theory.

Quite likely

>(This is certainly the case in our own tools and
>
>Question: would anyone care to confirm or deny that people do not rely on
>           rdfs:Class being member of itself
>          (in particular the RDF experts in this group)
>

Only to the extent that it answers what is otherwise a puzzling 
question, viz. what IS rdfs:Class a member of? (Do you want to 
suggest that RDF should have ramified types?)

>Question: is it really true that this would be all that much of a 
>change to RDF?
>           Syntactically? (My guess is no)

It would complicate the statement of the syntax, as far as I can see 
to no useful purpose.

>           Semantically?  (more so, but the model theory is still up for grabs)

It would have no effect on the model theory at all; the MT would be 
word-for-word identical.

>
>I would suggest that getting RDFS to accept a layered theory would 
>solve many of our problems with building OWL on top of RDFS.

I don't think so. I think it is completely irrelevant to those problems.

>Frank.
>    ----

Pat

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Received on Friday, 15 February 2002 03:41:47 GMT

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