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Re: [RDF+OWL] impossible to coreify OWL 2 RL combinations

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Tue, 31 Mar 2009 18:36:02 +0200
Message-ID: <49D24672.2060800@inf.unibz.it>
To: RIF WG <public-rif-wg@w3.org>
In the discussion in our meeting just now, besides the options I mentioned:

> So, either (a) we say that you effectively leave Core when going for OWL
> 2 RL or (b) we provide an embedding of an equality-free subset.
> I would be in favor of (a), because I do not want to define yet another
> OWL subset; I think the whole web of semantic Web languages is already
> complicated enough.

support was expressed for option (c) provide a general embedding in BLD,
but specify a subset of RIF-OWL combinations for which you stay in RIF
Core and for option (d) add an embedding of equality; this embedding
will depend on the predicate symbols used in the ruleset at hand.


Jos

Jos de Bruijn wrote:
> It is impossible to completely coreify the embedding of OWL 2 RL
> combinations, because there is equality in that language.  A nave
> axiomatization such as use of sameAs (as in [1]) is not sufficient,
> because in combinations one can use arbitrary predicates.
> 
> For example, if the ontology says:
> FunctionalProperty(p)
> ClassAssertion(C a)
> PropertyAssertion(p e a)
> PropertyAssertion(p e b)
> 
> With the nave sameAs axiomatization we can derive
> a[sameAs -> b] and b[rdf:type -> C]
> 
> However, if we add the RIF fact
> q(a)
> 
> we cannot derive q(b) unless we have a full-blown axiomatization of
> equality (which is doable because there are no function symbols in
> Core).  This would, however, clearly defeat the purpose of not having
> equality in Core.
> 
> So, either (a) we say that you effectively leave Core when going for OWL
> 2 RL or (b) we provide an embedding of an equality-free subset.
> I would be in favor of (a), because I do not want to define yet another
> OWL subset; I think the whole web of semantic Web languages is already
> complicated enough.
> 
> 
> Best, Jos
> 

-- 
+43 1 58801 18470        debruijn@inf.unibz.it

Jos de Bruijn,        http://www.debruijn.net/
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Received on Tuesday, 31 March 2009 16:36:53 GMT

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