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Re: Semantics of owl:imports

From: pat hayes <phayes@ai.uwf.edu>
Date: Sat, 9 Nov 2002 19:29:11 -0600
Message-Id: <p05111b02b9f364d900c0@[10.0.100.86]>
To: Jerome.Euzenat@inrialpes.fr (Jerome Euzenat)
Cc: www-webont-wg@w3.org

Hi Jerome

>Hello,
>
>First, I am not fanatical of interpreting owl:import as a triple 
>just like any other assertion. I think that this could be just like 
>owl:ontology (as in a recent P. Hayes mail), not in the graph but 
>replaced by its content (I understand that this cause problems 
>because if RDF does not understand this, then RDF and OWL 
>interpretations will diverge).
>
>This said, I am impressed by the logical jewellery that Pat is 
>deploying for accomodating this. For me it's breathtaking. I see 
>that this is a tricky game to arrange everything for RDF, RDFS and 
>OWL.
>
>I raise here an objection that I am not sure is valid (because I do 
>not master enough the semantics of RDF and OWL) but I am sure Pat 
>can quickly answer.
>
>The import are reintroduced as triple with a specially designed 
>semantics. In the short story:
>>Therefore, a document containing an I-import triple entails 
>>anything which is entailed by the imports closure of the document 
>>referred to be the object, in the usual sense of 'entails'.
>
>This looks like any one has abandonned the idea of 'reifying' 
>statements and applying negation of these?

Yes, reification is pretty much a dead idea, seems to me. I speak 
only for myself, of course.

>
>If not, what could be the negation of an import?

For the 'he-imports' case this would just be a simple negation. For 
the 'I-import' case, good question. Seems to me speaking intuitively 
that it ought to mean nothing at all, since to not import something 
is just not to 'do' anything to it, or not to take a stance about 
agreeing with it. Which means it ought to come out vacuously true. 
BUt thats what OUGHT to happen; I havnt checked through the details 
to see what actually happens.

>The problem that should be well known among non-compositionnal (non 
>verifunctionnal if I remember) constructs is if their negation 
>affects the importing action itself or its results

Im assuming the former, ie I dont think not-imports should be the 
same as imports-not

>(i.e., if the ontology does not import or if it imports the negation 
>of the imported statements). The negation of the sentence above 
>suggest that the document should entail the negation of what is 
>entailled by the import closure.

Well, yes, but only if you assume that there could be some 
surrounding negating expression, which isnt possible in RDF. If we 
could 'import in a context' then the definition of imports would have 
to get more subtle.

>
>Does it force to NOT entail the entailments of the import closure?

No. that wouldnt be practical. The most you could get would be that 
it was inconsistent with the imports closure, and I don't like even 
that.

>
>If not, then we have NOT(NOT(IMPORT(http://bla))) which is not the 
>same as IMPORT(http://bla). (Perfectly fine, but we've got to know 
>this).
>
>Another naïve remark: is it possible, in OWL/Full or RDFS to 
>subclass owl:Ontology

I hope not. This is why I said that owl:Ontology wasn't in the 
namespace, to avoid things like this.

Pat

>and to apply such rules as:
>
><owl:Class rdf:ID="theCrazyOne">
>	<rdfs:subClassOf rdf:resource="&owl;Ontology"/>
>	<rdfs:subClassOf>
>		<owl:complementOf/>
>			<owl:Restriction>
>				<owl:onProperty rdf:resource="&owl;imports"/>
>				<owl:hasValue rdf:resource="http://bla"/>
>			</owl:Restriction>
>		</owl:complementOf>
>	</rdfs:subClassOf>
></owl:Class>
>
>Sounds like the class of ontologies that do not import a particular 
>resource. This can be a perfectly meaningfull concept. But I am not 
>sure of its meaning that can is dependent of the answer to the 
>question above.
>
>Please forgive these unsufficiently informed interogations.
>--
>  Jérôme Euzenat                  __
>                                  /      /\
>  INRIA Rhône-Alpes,            _/  _   _   _ _    _
>                               /_) | ` / ) | \ \  /_)
>  655, avenue de l'Europe,    (___/___(_/_/  / /_(_________________
>  Montbonnot St Martin,       /        http://www.inrialpes.fr/exmo
>  38334 Saint-Ismier cedex,  /          Jerome.Euzenat@inrialpes.fr
>  France____________________/                Jerome.Euzenat@free.fr


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Received on Saturday, 9 November 2002 20:28:48 GMT

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