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Re: Anonymous individuals (again!)

From: Carsten Lutz <clu@tcs.inf.tu-dresden.de>
Date: Tue, 02 Dec 2008 18:03:06 +0100
To: Boris Motik <boris.motik@comlab.ox.ac.uk>
Cc: "'Jeff Z. Pan'" <jeff.z.pan@abdn.ac.uk>, public-owl-wg@w3.org
Message-id: <49356A4A.1000008@tcs.inf.tu-dresden.de>

Hi Boris,

Boris Motik wrote:
> 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.

I am not sure I understand. I had assumed that anonymous individuals can easily
be dealt with using the universal role and existential restrictions, both of which
are present in OWL 2 EL. Can you explain what you mean with "rolling up"?

thanks,
		Carsten

> 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

>>> 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.
> 
> 


-- 
*  Carsten Lutz, FB Mathematik und Informatik, Universitaet Bremen   *
* Office phone:++49 421 21864431 mailto:clu@informatik.uni-bremen.de *
Received on Tuesday, 2 December 2008 17:03:47 GMT

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