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Re: ISSUE-94 (n-ary constucts and RDF): Problem with roundtripping when going from functional-style syntax into RDF and back

From: Ivan Herman <ivan@w3.org>
Date: Thu, 17 Jan 2008 11:22:44 +0100
Message-ID: <478F2C74.80003@w3.org>
To: Boris Motik <boris.motik@comlab.ox.ac.uk>
CC: 'OWL Working Group WG' <public-owl-wg@w3.org>


Boris Motik wrote:
> Hello,
> 
> You are right in noting that 
> 
> EquivalentClasses( c_1 ... c_n )
> 
> does not introduce a new entity, at least not in the structural specification. It is also true that
> 
> _:x rdf:type owl11:AllEquivalentClasses
> _:x owl11:members T(SEQ c_1 ... c_n)
> 
> does introduce a new resource. This is, however, necessary because we do not have relations of arbitrary arity in RDF; hence, the
> only thing you can do is to reify the relation.
> 
> You should thing of the individual _:x as just being a "syntactic quirk". We don't want to say anything about it; we are just using
> it to encode an n-ary relation. This individual has exactly the same functionality as the blank nodes used to encode elements in an
> RDF list: you also have to introduce them in order to represent the list; however, you don't want to really do anything with them
> other than encode some n-ary syntax.
> 
> 
> Note also that this already occurs in OWL 1.0's owl:AllDifferent encoding of the DifferentIndividuals construct. Hence, the
> introduction of these new individuals for, say, EquivalentClasses does not introduce a precedent into the specification.
> 

Fair enough. (The OWL1.0 spec also looks a bit strange for the same 
reason, but, well, that is history...)

> I hope that this helps.
>

Yes, it does. Thanks

Ivan


> Regards,
> 
> 	Boris
> 
>> -----Original Message-----
>> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org] On Behalf Of Ivan Herman
>> Sent: 17 January 2008 09:47
>> To: OWL Working Group WG
>> Subject: Re: ISSUE-94 (n-ary constucts and RDF): Problem with roundtripping when going from
>> functional-style syntax into RDF and back
>>
>> Boris,
>>
>> I need a clarification.
>>
>> OWL Working Group Issue Tracker wrote:
>>> 4. Proposed solution
>>> --------------------
>>>
>>> The general approach to handling this issue would be along the lines of AllDifferent from OWL 1.0.
>> Consider again axiom (1). If n is equal to 2, then, to be compatible with OWL 1.0, we might translate
>> the axiom into (2). If n is different from 2, however, we would translate it into the following RDF
>> triples:
>>> (8) _:x rdf:type owl11:AllEquivalentClasses
>>> (9) _:x owl11:members T(SEQ c_1 ... c_n)
>>
>> My understanding is that
>>
>> EquivalentClasses( c_1 ... c_n )
>>
>> does not define any new entity, but makes a statement about existing
>> ones. However
>>
>> _:x rdf:type owl11:AllEquivalentClasses
>> _:x owl11:members T(SEQ c_1 ... c_n)
>>
>> introduces a new resource (_:x) and makes statement on that new
>> resource. Are these two really the same?
>>
>> I may have missed something, though
>>
>> Ivan
>>
>>
>>> There was some objection to the vocabulary bloat. However, most users are unlikely to deal with RDF
>> directly anyway: they will use editors for their ontologies, and these editors can hide the
>> underlying complexity.
>>>
>>> Regards,
>>>
>>> 	Boris
>>>
>>>
>>>
>>>
>> --
>>
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>> FOAF: http://www.ivan-herman.net/foaf.rdf
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf


Received on Thursday, 17 January 2008 10:22:51 GMT

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