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RE: ISSUE 131 (OWL R Unification): Different semantics on syntactic fragment

From: Michael Schneider <schneid@fzi.de>
Date: Tue, 12 Aug 2008 16:05:55 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A0AD96FF@judith.fzi.de>
To: "Ian Horrocks" <Ian.Horrocks@comlab.ox.ac.uk>
Cc: <public-owl-wg@w3.org>
I will answer this question:

Ian Horrocks wrote:

>Michael,

[...]

>As I understand it, your proposed "solution" to this problem is to
>retain OWL RL Full,

Yes.

>and make its semantics be defined by the rule set

Yes.

>(which, as a result of a very poor decision we made that the 2nd F2F,
>is implicitly the case in the existing spec). 

Indeed, that's how I understand the status quo (I disagree that this was a
poor decision).

>This means introducing a 3rd semantics for OWL: 

Without wanting to dive into this recurrent "this is counter intuitive"
argument again, I want to only say this: 

The W3C recommendations "Simple Entailment", RDF, RDFS and OWL 1 Full all
have pair wise different semantics, and all of them will have a different
semantics compared with OWL 2 Full. And that's also the case for pD*, and
all of Jena's rule based OWL sublanguages on the non-standards side. 

"Different semantics" means that for every two such languages there always
exists an RDF graph, which is interpreted differently by the two languages.
It's a distinguishing property of RDF based languages that they differ
w.r.t. their *semantics*. Unlike description logics, RDF based languages
cannot be distinguished by their respective syntax, because they always have
the same syntax: RDF. 

This might look inconvenient from a description logics perspective. But it
is natural from an RDF semantics perspective. And it's not uncommon for
certain other families of logics, either, btw. So, nothing "absurd" is going
on here with a "third semantics", at least not technically.

Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
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Email: Michael.Schneider@fzi.de
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Received on Tuesday, 12 August 2008 14:14:42 GMT

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