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RE: Proposal and Test cases (Re: skolems: visible differences?)

From: Michael Schneider <schneid@fzi.de>
Date: Thu, 17 Jan 2008 16:06:15 +0100
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A06C249D@judith.fzi.de>
To: "Bijan Parsia" <bparsia@cs.man.ac.uk>, "Jeremy Carroll" <jjc@hpl.hp.com>
Cc: "Web Ontology Language ((OWL)) Working Group WG" <public-owl-wg@w3.org>
Bijan Parsia answered to Jeremy Carroll:

>You mean Michael's? I thought it was based on his misunderstanding of  
>how bnodes work.

To be precise: It was a misunderstanding of how /skolems/ work.

>Basically, he thought they worked the way "_" does in prolog, when in  
>fact they work like "_SomeIdentifier", with the scope being graphs  
>rather than clauses.
>
>And I agree that if sameAs(_:y, _:y) were not necessarily true that  
>the user who is me would certainly be confuse :)

This example ontology shows my misunderstanding:

  DifferentIndividuals(_:y _:y)

Under existential bNode semantics, this ontology is *inconsistent*.

If skolems would work the way I /thought/ ("a fresh variable for each
occurrence"), than this ontology would be *consistent*, since the two
occurrences of '_:y' would then be allowed to be interpreted differently. 

Since it is known that skolems and existentials behave equivalently wrt
consistency of an ontology, this cannot be, hence I must be wrong.

Thanks, Bijan and Jeremy!

Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
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Received on Thursday, 17 January 2008 15:06:35 GMT

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