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RE: Anonymous individuals (again!)

From: Boris Motik <boris.motik@comlab.ox.ac.uk>
Date: Tue, 2 Dec 2008 16:13:06 -0000
To: "'Jeff Z. Pan'" <jeff.z.pan@abdn.ac.uk>
Cc: <public-owl-wg@w3.org>
Message-ID: <0BF23B78DABE4348B9FDF784384630CF@wolf>

Hello,

The general approach to handling anonymous individuals is that you should roll them up into a concept. Now, according to the
restrictions in the Syntax document, you might need inverse roles for that; OWL 2 EL doesn't have inverses, so there you go.

In OWL 2 QL, you can roll anonymous individuals into concepts. To decide satisfiability, you need to negate these concepts and put
them into the ontology; but then, existentials become universals, which you don't have in OWL 2 QL. There is another problem: if you
wanted to extend OWL 2 QL with functionality (which was deliberately left as a possibility), you must ensure that all individuals in
the ABox are interpreted under UNA if you want query answering to be first-order reducible. That's a problem for anonymous
individuals: they are not naturally interpreted under UNA, and, if you have such individuals distributed over imported ontologies,
you can't even axiomatize UNA yourself (because anonymous individuals are unique to the ontology they are contained in).

Regards,

	Boris

> -----Original Message-----
> From: Jeff Z. Pan [mailto:jeff.z.pan@abdn.ac.uk]
> Sent: 02 December 2008 15:16
> To: Boris Motik
> Cc: public-owl-wg@w3.org
> Subject: Re: Anonymous individuals (again!)
> 
> Hi Boris,
> 
> Thanks for the hard work. Are there any examples to illustrate why we
> can have anonymous individuals in OWL 2 RL but not the other two profiles?
> 
> Thanks,
> 
> Jeff
> 
> 
> 
> Boris Motik wrote:
> > Hello,
> >
> > The problems with anonymous individuals that I noticed in the Profiles made me look again at the
> global restrictions on anonymous
> > individuals in Section 11.2. I noticed a slight error in the global restrictions, which I've fixed.
> After fixing this error, I
> > realized that
> >
> > - the restriction on no anonymous individuals in OWL 2 EL and OWL 2 QL is strictly needed if we
> don't want to lose good
> > computational properties;
> >
> > - however, in OWL 2 RL this restriction isn't needed -- that is, even with anonymous individuals
> reasoning in OWL 2 RL can be
> > implemented in polynomial time.
> >
> > Consequently, I've removed the restriction on no anonymous individuals in OWL 2 RL from the
> Profiles document.
> >
> > I'm now done with all my changes to the spec -- we are ready to roll!
> >
> > Regards,
> >
> >       Boris
> >
> >
> >
> > The University of Aberdeen is a charity registered in Scotland, No SC013683.
> >
> >
> 
> 
> 
> The University of Aberdeen is a charity registered in Scotland, No SC013683.
Received on Tuesday, 2 December 2008 16:13:53 GMT

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