- From: <gstoil@image.ece.ntua.gr>
- Date: Thu, 8 Nov 2007 12:05:38 -0000
- 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 UTC