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Re: ISSUE-3: REPORTED: Lack of anonymous individuals

From: <gstoil@image.ece.ntua.gr>
Date: Thu, 8 Nov 2007 12:05:38 -0000
Message-Id: <200711081205.lA8C5cMq014164@manolito.image.ece.ntua.gr>
To: Uli Sattler <sattler@cs.man.ac.uk>, gstoil@image.ece.ntua.gr
Cc: Boris Motik <boris.motik@comlab.ox.ac.uk>, public-owl-wg@w3.org, Carsten Lutz <clu@tcs.inf.tu-dresden.de>

gstoil@image.ece.ntua.gr said:

> 
> Uli Sattler <sattler@cs.man.ac.uk> said:
> 
> > 
> > 
> > On 8 Nov 2007, at 11:12, <gstoil@image.ece.ntua.gr> wrote:
> > 
> > >
> > > Boris Motik <boris.motik@comlab.ox.ac.uk> said:
> > >
> > >>
> > >> Hello,
> > >>
> > >> The OWL 1.1 Member Submission does not contain anonymous  
> > >> individuals for the
> > > reasons I explain below. These reasons are related to
> > >> ISSUE-46: Unnamed Individual Restrictions
> > > (http://www.w3.org/2007/OWL/tracker/issues/46). It might make sense  
> > > to discuss
> > > both issues
> > >> together.
> > >>
> > >> In short, we did not include the anonymous individuals into the  
> > >> Member
> > > Submission because they significantly affect computational
> > >> aspects of the logic (explained under item 1 below). Furthermore,  
> > >> anonymous
> > > individuals are usually used in practice with a weaker
> > >> semantics (explained under item 2 below). Therefore, we did not  
> > >> introduce
> > > anonymous individuals in the Member Submission and wanted
> > >> to discuss this in the working group.
> > >>
> > >>
> > >>
> > >> 1. Why can nontree-like "true" anonymous individuals be dangerous?
> > >>
> > >> Nontree-like "true" anonymous individuals in the ABox cause  
> > >> undecidability
> > > of ontology entailment, which is the basic inference
> > >> problem for OWL. An ABox containing anonymous individuals can  
> > >> actually be
> > > understood as a conjunctive query. It is well known that
> > >
> > > Hi Boris,
> > >
> > > Is it a conjunctive query or a union of conjunctive queries?
> > >
> > 
> > Hi Giorgos,
> > 
> > this dangerous stems from single conjunctive queries: see
> > 
> > http://www.inf.unibz.it/~calvanese/papers/calv-degi-lenz-PODS-98.pdf
> > or
> > http://www.springerlink.com/content/5g64t33487111134/fulltext.pdf
> > 
> 
> Hi Uli,
> 
> Thanks much for the refs. 
> 
> Hmmm, so this also means that the problem is even undecidable for some of the
> tractable fragments, like EL++, but probably not for EL, ELH and DL-Lite,
> maybe not also for RDFS and DLP, right?

A! also EL++ with the SROIQ restriction on RIAs should be OK, right?

> 
> Greetings,
> -gstoil
> 
> > 
> > > BTW, can you explain more how you can view anonymous individuals as  
> > > CQs?
> > >
> > 
> > simply because, if you allow them in an ontology, then you can reduce  
> > entailment of CQs to entailment between ontologies: simply view the  
> > CQ as an ontology with anonymous individuals!
> > 
> > The reason why skolem constants are more harmless is because they are  
> > simply names for domain elements like normal constants (but the  
> > "anonymous individuals as skolem constants" would free you from  
> > having to invent a proper name for them)  -- and, when you are trying  
> > to see whether an interpretation is a model of an ontology, you don't  
> > need to find an appropriate mapping!
> > 
> > Cheers, Uli
> > 
> > > Best,
> > > G. Stoilos
> > 
> > 
> > 
> 
> 
> 
> -- 
> 
> 
> 
> 



-- 
Received on Thursday, 8 November 2007 12:06:57 GMT

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