- From: pat hayes <phayes@ai.uwf.edu>
- Date: Fri, 25 Oct 2002 11:48:24 -0500
- To: Ian Horrocks <horrocks@cs.man.ac.uk>
- Cc: www-webont-wg@w3.org
>On October 24, pat hayes writes: >> >> >There may be pragmatic/implementation reasons to go for implies >> >semantics in all cases: >> > >> >- it can only lighten the burden on implementors as there will be >> >fewer kinds of logical entailment to worry about. >> > >> >- the cost isn't very great as implied functionality, transitivity >> >etc. due to strange constraints on possible models doesn't seem like >> >it would be of great interest. >> > >> >- it would satisfy Pat's complaint that logically entailed range and >> >domain restrictions are positively harmful. >> >> But it would fail to satisfy the RDFS requirement that subClassOf and >> subPropertyOf are transitive. We could of course just add this as an >> ad-hoc semantic requirement, but that seems very tacky. > >I'm not sure what your point is here. Are you concerned as to whether >subClassOf and subPropertyOf are implicitly instances of >owl:TransitiveProperty? I do not believe that this would not be a >valid Fast OWL inference (or at least not a question one could ask). No, its purely an RDFS matter. The RDFS spec requires that the RDFS semantics impose the condition that rdfs:subClassOf and rdfs:subPropertyOf are transitive. Of course you cannot SAY this in RDFS, but it is nevertheless required. The 'IF' semantics does not guarantee that the subClass/Property relations are transitive, as Peter noticed a while back. This would indeed presumably mean that rdfs:subClassOf rdf:type owl:TransitiveProperty . would be valid in OWL. (Even fast OWL. right?). > >> Given the option between all IF and all IFF, I think the all-IFF >> option is more coherent. But I would prefer a more tailored solution, >> as you know. > >I prefer all IF for the reasons I have mentioned, in particular the >possible extra burden on implementors. E.g., it isn't clear that these >entailments can be reduced to satisfiability and still stay within OWL >Lite (it might be possible, but not via the reductions we have >mentioned up to now as these rely on nominals), so these entailments >might make it harder to implement a complete OWL Lite reasoner. Hmmm. But these are definitely required for RDFS, so this may be an issue for OWL Lite to look at more seriously. I don't think that it would be kosher for OWL lite to assume that part of the meaning of any RDFS term was, as it were, removed in OWL. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Friday, 25 October 2002 12:48:27 UTC