RE: Proposal to resolve ISSUE-81

Hi, Alan!

>-----Original Message-----
>From: public-owl-wg-request@w3.org 
>[mailto:public-owl-wg-request@w3.org] On Behalf Of Alan Ruttenberg
>Sent: Sunday, March 23, 2008 3:48 PM
>To: Web Ontology Language ((OWL)) Working Group WG
>Subject: Proposal to resolve ISSUE-81
>
>
>To resolve this issue I propose that NegativeObjectPropertyAssertion  
>be transformed into the equivalent class assertion. In order to  
>support tools that wish to preserve the presentation of this axiom as  
>NegativeObjectPropertyAssertion we use the axiom annotation mechanism  
>with a new annotation property: syntaxHint.  syntaxHint would be  
>considered optional - not all tools need serialize using it, nor all  
>tool pay attention to it.
>
>So
>NegativeObjectPropertyAssertion(hasMother John Mary)
>
>Is translated in to
>
>ClassAssertion(
>   Annotation(syntaxHint NegativeObjectPropertyAssertion)
>   John ObjectAllValuesFrom(hasMother ObjectComplementOf(ObjectOneOf 
>(Mary))))

I will only talk here about having this as an RDF syntax for negative property assertions. I won't talk about the functional syntax.

I would not totally object to your proposal, but let me say that I have a personal preference for a more direct encoding.

Aside from the round-tripping issue (ignoring your "syntaxHint" annotation for the moment :-)), I can also see a slight semantic issue with the above encoding, in particular for /data/ property assertions. I feel that the following idea might be worth to be considered: Statements of the form

  NegativeDataPropertyAssertion(dp s o)

should be allowed, where 'dp' denotes a data property, and 'o' denotes an individual(!) instead of a datavalue. The reason is that I just want to state that the triple "s p o" does *not* exist, and for an 'o', which does *not* denote a datavalue, this is, of course, always a true assertion. 

This is probably a controversial idea. Whatever one's opinion is here, the approach given by the above encoding will *not* support this idea:

  * In Full, the object o will be coerced into a datavalue, which may lead to undesired semantical side effects in certain situations.

  * In DL, if 'o' is an individual, then this will produce an error, AFAICS. [FIXME: There is no individual/datavalue punning in 1.1-DL, since URIs cannot denote datavalues?] 

These effects can at least be technically avoided with a direct encoding such as the current one based on reification. One can, of course, opt to introduce these effects explictly in such a direct encoding. Anyway, one has then the /option/ to do so. So what my idea at least shows is that the above encoding of negative property assertions carries perhaps a bit more information than necessary.

But again, as for ISSUE-67, I prefer to avoid RDF reification (again for political reasons in the first place), and would instead opt to introduce a dedicated feature specific vocabulary:

  _:x rdf:type owl11:NegativeObjectPropertyAssertion 
  _:x owl11:propertyAssertionSubject s
  _:x owl11:propertyAssertionPredicate p
  _:x owl11:propertyAssertionObject o

And analog for 'owl11:NegativeDataPropertyAssertion' (I won't argue about names, though).

>-Alan
>
>meta: ISSUE-103

Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
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