- From: Boris Motik <boris.motik@comlab.ox.ac.uk>
- Date: Tue, 2 Dec 2008 17:58:18 -0000
- To: <clu@tcs.inf.tu-dresden.de>
- Cc: "'Jeff Z. Pan'" <jeff.z.pan@abdn.ac.uk>, <public-owl-wg@w3.org>
Hello, Assume that you have the following ABox: (1) R(a, _:x1) (2) S(b, _:x1) (3) T(_:x3, _:x1) The global restrictions ensure that anonymous individuals occur in tree-shaped assertions, which is the case here. Now you can eliminate these assertions by replacing these three assertions with the following one: (4) \exists R.[(\exists S^-.{ b }) \sqcap (\exists T^-.\top)](a) The problem is, however, that assertions containing anonymous individuals can be arbitrarily oriented; hence, you might need inverse roles for rolling up. Since inverse roles are not available in OWL 2 EL, you can't make this encoding, which is why I thought one cannot handle the damn thing in OWL 2 EL. I'm open to suggestions if you have some other idea. Regards, Boris > -----Original Message----- > From: clu@tcs.inf.tu-dresden.de [mailto:clu@tcs.inf.tu-dresden.de] > Sent: 02 December 2008 17:03 > To: Boris Motik > Cc: 'Jeff Z. Pan'; public-owl-wg@w3.org > Subject: Re: Anonymous individuals (again!) > > 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 17:59:11 UTC