- From: Uli Sattler <sattler@cs.man.ac.uk>
- Date: Thu, 8 Nov 2007 11:27:01 +0000
- To: <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>
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 > 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 11:27:13 UTC