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Re: Some basic questions about OWL-Full

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 22 Oct 2007 15:23:17 -0500
Message-Id: <p06230908c342b53847b1@[192.168.1.2]>
To: "Michael Schneider" <schneid@fzi.de>
Cc: "Owl Dev" <public-owl-dev@w3.org>

>Hi!
>
>OWL-Full has ever been a complete mystery to me, and I admit that I have
>never really made an approach to explore it. But now that people have
>started to work on a new version of OWL, I think it is a good time for me to
>at least try to learn a few fundamental facts. So dear OWL-Full experts: I
>will put a few questions, all very basic, and all of them can be answered by
>just saying "yes" or "no". But I won't bite you if you also add a small
>explanation to each of your answers. :)
>
>(1) My first question is about syntactically correct OWL-Full ontologies. I
>always thought that simply "everything" is allowed in OWL-Full. So my
>question: Is every RDF graph an allowed OWL-Full ontology?

Yes. Of course, it might be self-contradictory in OWL-Full.

>
>(2) The rest of my questions all deal with semantics. I think I have heard
>somewhere that one can "change the semantics" of OWL-Full itself by stating
>axioms about OWL vocabulary, but I don't know if this is true, and not even
>what this exactly means. Ok, let's test this by creating a concrete example!
>I would have said that the following two statements lead to inconsistency
>even in OWL-Full:
>
>   :x owl:sameAs :y .
>   :x owl:differentFrom :y .

Indeed.

>
>But what if I add the following axiom:
>
>   EquivalentProperties(owl:sameAs owl:differentFrom)
>
>This should at least be syntactically ok in OWL-Full (see (1)).

It is syntactically OK, but it is logically contradictory.

>  But have I
>also managed to make this ontology semantically consistent with this trick?

No. OWL-Full does not allow you to 'cancel' any 
of the OWL semantic assumptions; it allows you to 
contradict them, so to speak, but then you have 
uttered an OWL contradiction.

>I don't believe so, but I am also not certain. And whatever answer is
>correct, I do not have an explanation for any of them.
>
>(3) A more general question: Is it true that whenever an OWL-DL ontology is
>inconsistent under OWL-DL semantics, then it is also inconsistent under
>OWL-Full semantics? Would sound reasonable to me, but I am not sure.

I am not sure, either, as the relationship 
between OWL-DL and OWL-Full was made rather 
complicated late in the process, and I am not 
sure of its exact status. Peter (PFPS) had the 
idea of arranging things so that for any graph 
that satisfied the DL syntactic restrictions, 
that Full and DL entailment would coincide. I was 
not sure that this would be possible, and I am 
still not sure whether this was in fact managed.

The issue is that something can be a Full 
interpretation (even a model) without its being a 
legal DL model: which would suggest that might be 
expressions which are DL-unsatisfiable yet Full 
satisfiable. What Peter was trying to do was 
ensure that this only happened when the 
expression was also DL-syntactically-illegal.

>
>(4) Looking at both questions (2) and (3) brings me to my last question. The
>ontology in question (2) is *not* an allowed OWL-DL ontology, of course, but
>it contains a sub-ontology which is syntactically allowed in OWL-DL: The
>first two statements above. So I ask if the following claim is true: "Given
>that an OWL-Full ontology contains an OWL-DL sub-ontology, which is
>inconsistent under OWL-DL semantics, then the complete OWL-Full ontology is
>inconsistent under OWL-Full semantics." Is this true or wrong?

That is correct, yes, as DL-entailment implies Full entailment.

>
>Ok, I think that this is enough for me for the moment to get a first feeling
>for OWL-Full.
>
>Cheers,
>Michael
>
>--
>Dipl.-Inform. Michael Schneider
>FZI Forschungszentrum Informatik Karlsruhe
>Abtl. Information Process Engineering (IPE)
>Tel  : +49-721-9654-726
>Fax  : +49-721-9654-727
>Email: Michael.Schneider@fzi.de
>Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555
>
>FZI Forschungszentrum Informatik an der Universität Karlsruhe
>Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
>Tel.: +49-721-9654-0, Fax: +49-721-9654-959
>Stiftung des bürgerlichen Rechts
>Az: 14-0563.1 Regierungspräsidium Karlsruhe
>Vorstand: Rüdiger Dillmann, Michael Flor, Jivka Ovtcharova, Rudi Studer
>Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus


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Received on Monday, 22 October 2007 20:23:36 GMT

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