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RE: [OWLWG-COMMENT] Punning and the "properties for classes" use case

From: Michael Schneider <schneid@fzi.de>
Date: Mon, 5 Nov 2007 21:42:37 +0100
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A04A8F93@judith.fzi.de>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: <public-owl-dev@w3.org>

Hi, Peter!

Peter F. Patel-Schneider wrote:

>From: "Michael Schneider" <schneid@fzi.de>
>Subject: RE: [OWLWG-COMMENT] Punning and the "properties for 
>classes" use case 
>Date: Mon, 5 Nov 2007 10:24:32 +0100
>
>> Hi again, Peter!
>> 
>> I see that I still have several concrete problems in 
>understanding punning,
>> before I can answer your other mails. Here is the next question:
>> 
>> Peter F. Patel-Schneider wrote:
>> 
>> >Well, in OWL 1.1, it is true that 
>> >
>> >	Declaration(Individual(a))
>> >	Declaration(OWLClass(a))
>> >	Declaration(Individual(b))
>> >	Declaration(OWLClass(b))
>> >	SameIndividual(a b)
>> >
>> >does not entail
>> >
>> >	EquivalentClasses(a b)
>> 
>> My question is /not/ about this claim, 
>
>My mistake then.
>
>> but about RDF mapping. I want to
>> know: Given an OWL-1.1 ontology in functional style syntax, 
>in which punning
>> is used. How is such an ontology mapped to RDF? As an 
>example, let's take
>> the above six axioms:
>> 
>>   Declaration(Individual(a))
>>   Declaration(OWLClass(a))
>>   Declaration(Individual(b))
>>   Declaration(OWLClass(b))
>>   SameIndividual(a b)
>>   EquivalentClasses(a b)
>> 
>> How do these axioms get mapped to RDF? I can imagine two 
>different mappings:
>> 
>> A: Each URI ref in the functional syntax version gets 
>directly mapped to the
>> same URI ref in the resulting RDF graph:
>> 
>>   <a> owl11:declaredAs owl11:Individual .
>>   <a> owl11:declaredAs owl:Class .
>>   <b> owl11:declaredAs owl11:Individual .
>>   <b> owl11:declaredAs owl:Class .
>>   <a> owl:sameAs <b> .
>>   <a> owl:equivalentClass <b> .
>>   
>> B: The URI refs get explicitly separated:
>> 
>>   <a_Thing> owl11:declaredAs owl11:Individual .
>>   <a_Class> owl11:declaredAs owl:Class .
>>   <b_Thing> owl11:declaredAs owl11:Individual .
>>   <b_Class> owl11:declaredAs owl:Class .
>>   <a_Thing> owl:sameAs <b_Thing> .
>>   <a_Class> owl:equivalentClass <b_Class> .
>
>Well, looking at the RDF mapping document gets you the 
>(current) answer,
>which is A (roughly).   (There are also typing tripes generated.)
>
>> As far as I understand it: If punning allows to denote semantically
>> unrelated individuals and classes by the same URI ref in 
>functional syntax,
>> than mapping A would change the original semantics of the 
>ontology, while
>> this semantics would be preserved by mapping B. But otherwise, if an
>> individual and a class having the same name are intended to 
>be the same
>> entity, than mapping A would be a correct mapping, while B 
>would also allow
>> interpretations where the individual and the class are semantically
>> unrelated.
>
>No.  From the RDF mapping document:
>
>	OWL 1.1 ontologies serialized in RDF/XML are interpreted by
>	translating them into the functional-style syntax and applying
>	the OWL 1.1 semantics.
>
>So the OWL 1.1 meaning of the triples is defined in the OWL 1.1
>Semantics document, just as the semantics of an OWL DL ontology is
>defined by the direct model-theoretic semantics for OWL DL no matter
>what form it is written in.

Ok, this is pretty clear to understand, but it surprises and concerns me. As
far as I have understood the facts, in OWL-DL there hasn't been a conflict
between the direct model theoretic semantics, and the DL version of the RDF
compatible semantics. But now it looks different to me. Let's start from the
above ontology encoded in RDF in the form "A" (see above) together with the
two missing typing axioms you mention below. Now the mapping document says
that in order to learn the semantics of this ontology, I have to map the RDF
graph into functional style syntax, and then look up the OWL-1.1 semantics
from the semantics document. 

But how is an RDF compatible semantics possible in this case? An RDF
compatible semantics won't allow interpretations for which a class denoted
by "<u>" is semantically unrelated to an individual denoted also by "<u>",
right? But this is allowed by OWL-1.1 "direct" semantics, if I correctly
understand it. Or to make it more explicit: Is it correct or false that in
OWL-1.1 with punning, I am allowed to interprete some given URI ref <u> with
both

  (a) an /arbitrary/ individual from the universe
  (b) an /arbitrary/ class from the universe

?

In OWL-DL, this problem did not exist, because the RDF graphs of OWL-DL
ontologies never used URI refs both as individuals and classes. And for
OWL-Full, where such a duplicate usage was actually allowed, there was only
RDF compatible semantics, no direct semantics, so no conflict could arise.

So if punning allows interpreting the same URI refs by semantically
unrelated individuals and classes (i.e. arbitrarily chosen combinations of
individuals and classes): Dosn't this mean that an RDF compatible semantics
will not be possible for OWL-1.1?

Cheers,
Michael


>So even if the mapping was changed, the semantics would remain 
>the same.
>
>> So only one of these mappings should be allowed. But I 
>cannot find out from
>> the "RDF mapping" draft which mapping is correct. Probably, 
>I have only
>> overlooked the important bits in the draft?
>
>Well, you have to follow the RDF mapping a bit.  Consider
>
>	EquivalentClasses(a b)
>
>Its transformation generates the triple
>
>	T(a) owl:equivalentClass T(b)
>
>because a and b occur in the functional syntax as owlClassURI, their
>transformation, T(a) and T(b), generates the triples
>
>	a rdf:type owl:Class
>	b rdf:type owl:Class
>
>and T(a) is a and T(b) is b in the first triple.  A little examination
>of the mapping will show that there is no modification of URIs in the
>mapping.  (Yes, I agree that the mapping is quite hard to read.)
>
>> Cheers,
>> Michael
>
>peter
>

--
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 Monday, 5 November 2007 20:42:55 GMT

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