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Re: Reconciliation of concerns, re islands and dataset semantics?

From: Ivan Herman <ivan@w3.org>
Date: Thu, 1 Mar 2012 13:41:43 +0100
Cc: Pat Hayes <phayes@ihmc.us>, W3C RDF WG <public-rdf-wg@w3.org>
Message-Id: <3C423B02-5494-4401-950C-AD2E40274599@w3.org>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>

On Mar 1, 2012, at 13:31 , Antoine Zimmermann wrote:
[snip]
>> 
>> If (:a owl:sameAs :b) and (:a owl:differentFrom :b) appeared in the
>> same graph, then an OWL reasoner, using the definition of the
>> predicates, would deduce that there is a inconsistence. I mean: the
>> triples themselves are just fine, it is up to a reasoner to find the
>> problem.
>> 
>> If they are in different graphs, then the inconsistence would not
>> occur, because we only care about the models in separate graphs,
>> independently from one another.
> 
> Hmm, this seems to contradict what you said above. If URIs are interpreted identically in all graphs with overlapping vocabularies, how can :a be interpreted as the same thing as :b and at the same time as something different then :b? Either you have an inconsistency, or you interpret the URIs differently in the two graphs.
> 

"Same thing" does not exist in RDF semantics, afaik. The only thing that exist are triples and other triples that can be deduced thereof. In my understanding, it is perfectly fine to put, into the same graph, the triples

(:a owl:sameAs :b)
(:a owl:differentFrom :b)

and an interpretation 'I' can map :a and :b onto *different* elements in the target set (or, even, they have to do that?). It is only when an OWL reasoner looks at these triples that it will shout because the semantic condition for an OWL-interpretation are violated if that happens due to the special semantics of sameAs and differentFrom.

If we have

G1 {(:a owl:sameAs :b)}
G2 {(:a owl:differentFrom :b)}

The OWL reasoner will look only at I|G1 and I|G2, respectively, and in those constrained environment no inconsistency occurs.


>> [...]
>> 
>>> 
>>> Now, if you want to do temporal reasoning, provenance, trust, it's
>>> more complicated. But the fierceful rejection by Pat on the mere
>>> idea of a multi-interpretation semantics has deviated the
>>> discussion away from these issues.
>> 
>> And I do not think this working group should deal with temporal
>> reasoning, provenance, or trust. Just giving the basis in terms of
>> that semantics is what should be done.
> 
> I do not mean the WG should provide a standard for temporal reasoning etc. I just mean that we have to analyse these use cases in light of the various options we have for defining a semantics of datasets/quads/multiple-graph structure.

Ok.

Ivan

----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
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Received on Thursday, 1 March 2012 12:41:56 GMT

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