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

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?

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 11:45:57 UTC