- From: Ivan Herman <ivan@w3.org>
- Date: Fri, 23 Jan 2009 11:42:39 +0100
- To: Boris Motik <boris.motik@comlab.ox.ac.uk>
- CC: 'W3C OWL Working Group' <public-owl-wg@w3.org>
- Message-ID: <49799F1F.7050509@w3.org>
Each new datatype has to be implemented somehow (interpretation of the lexical space rules, relationships to other, etc, etc). The implementation of any of those can be non-trivial. So we are just adding new and new non-trivial things. Ivan Boris Motik wrote: > Hello, > > I agree that the implementation of datatypes is nontrivial in OWL 2 RL. This, however, is already the case for the existing > datatypes. I really cannot see how the datatypes that we left out would make the implementation any harder. > > Regards, > > Boris > >> -----Original Message----- >> From: Ivan Herman [mailto:ivan@w3.org] >> Sent: 23 January 2009 08:51 >> To: Boris Motik >> Cc: 'W3C OWL Working Group' >> Subject: Re: A slight issue with datatypes in OWL 2 RL >> >> Boris, >> >> before we do this... let me just raise this issue: just because we _can_ >> does not meant that we necessarily _should_. >> >> In my view, one of the goals of RL is a possibility for an easy >> implementation, too. With my limited implementation experience the >> datatype handling of RL is by far the most complex part of an >> implementation. Sure, if one goes for a very efficient implementation >> then taking care of things like owl:sameAs becomes also more complex, >> but that is not 100% necessary for a compliant thing. Datatype handling >> is. (I actually did not even have the time to implement it, I just rely >> on the underlying RDF/Python environment and do whatever it can do. I >> can see many implementations doing just that.) Oracle has already >> indicated that they are not really in favour of an owl:rational >> inclusion in OWL RL, and I think their reaction reflects the same concerns. >> >> Based on this I actually do _not_ believe that this is just an editorial >> comment but would definitely warrant a new LC round because it would >> significantly add to the complexity of implementations. My personal >> interpretation (maybe wrong!) of that comment in the document is that >> some datatypes (like rational) may actually be dropped from the list and >> not add all other datatypes blindly... >> >> My 2 cents...:-) >> >> Ivan >> >> Boris Motik wrote: >>> Hello, >>> >>> Here is a Last Call comment about datatypes in OWL 2 RL. This issue was pointed out by Jos de >> Bruijn during the RIF integration >>> meeting, and I remembered it today after a private discussion about datatypes with Zhe. Thanks to >> both of them! >>> Currently, OWL 2 RL disallows certain datatypes on the grounds that reasoning with them would not >> be polynomial. Now we could >>> actually relax this restriction and allow all OWL 2 datatypes to occur in OWL 2 RL ontologies. >>> >>> This is actually an oversight of mine, caused by the following technical issue. OWL 2 EL and OWL 2 >> QL have existential quantifiers; >>> hence, you can state existence of concrete objects whose values is not known precisely. But then, >> if you allow combinations of >>> datatypes such that the intersection of possibly negated datatypes is finite, you really do get >> into problems: your reasoning >>> suddenly becomes NP-hard because you need to start guessing the appropriate value of existentially >> implied object. To prevent this >>> from occurring, I selected the set of allowed datatypes in OWL 2 EL such that each intersection of >> possibly negated datatypes is >>> either empty or infinite; then, I merely copied this set to all the profiles. >>> >>> As Jos rightly pointed out at the RIF integration meeting, however, OWL 2 RL *does not* have >> existential quantifiers; consequently, >>> the value of each concrete object is fully known. But then, there is no need to actually restrict >> the set of datatypes: to support a >>> datatype, you just need a procedure that recognizes whether some literal is in the range of a >> particular datatype (which is easy to >>> do for all of OWL 2 datatypes). >>> >>> >>> The fix to this comment would be to revise the datatypes section for OWL 2 RL and allow all OWL 2 >> datatypes to occur in OWL 2 RL >>> ontologies. Since we already have a note saying that the set of supported datatypes might change, I >> believe that this change would >>> not warrant another Last Call round. >>> >>> I'm really sorry about this oversight! >>> >>> Regards, >>> >>> Boris >>> >>> >> -- >> >> Ivan Herman, W3C Semantic Web Activity Lead >> Home: http://www.w3.org/People/Ivan/ >> mobile: +31-641044153 >> PGP Key: http://www.ivan-herman.net/pgpkey.html >> FOAF: http://www.ivan-herman.net/foaf.rdf > -- Ivan Herman, W3C Semantic Web Activity Lead Home: http://www.w3.org/People/Ivan/ mobile: +31-641044153 PGP Key: http://www.ivan-herman.net/pgpkey.html FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Friday, 23 January 2009 10:43:12 UTC