- From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
- Date: Mon, 9 Feb 2009 10:53:47 +0000
- To: Bijan Parsia <bparsia@cs.man.ac.uk>
- Cc: W3C OWL Working Group <public-owl-wg@w3.org>
On 30 Jan 2009, at 16:51, Bijan Parsia wrote: > > On 21 Jan 2009, at 19:31, Bijan Parsia wrote: > >> Done with: >> http://www.w3.org/2007/OWL/wiki/index.php? >> title=Syntax&oldid=17348 [Bijan Parsia] >> >> To: >> http://www.w3.org/2007/OWL/wiki/Syntax#Keys > > In working on the draft reply, I was wondering if my change was > enough, or if it should read: > > """A key axiom of the form HasKey( owl:Thing OPE ) is similar to > the axiom InverseFunctionalProperty( OPE ), the main differences > being that the former axiom is applicable only to individuals that > are explicitly named in an ontology, while the latter axiom is also > applicable to individuals whose existence is implied by existential > quantification. Furthermore, an inverse-functional property is > inverse-functional for all assertions using that property, whereas > keys can be scoped to assertions involving individuals of a certain > class."""" > > Add: """In this way, classes can represent distinct tables with the > same key name or different versions of the same table directly.""" OK for me -- and it may help people (like Jim) coming from DB backgrounds to understand the rationale. > > If this is ok, I'll add it. > > Also, I think this is misleading: > > """This makes key axioms equivalent to a variant of DL-safe rules > [DL-Safe]. Thus, key axioms will typically not affect class-based > inferences such as the computation of the subsumption hierarchy, > but they will play a role in answering queries about individuals. > This choice has been made in order to keep the language decidable.""" > > DL safe rules require DL safety to be decidable (to a first > approximation). Keys *do not*. We restrict keys for implementation > considerations. I agree -- the last sentence is simply wrong. We could simply delete this sentence: I don't think that we want or need to justify all design choices in this document, and it might be difficult to provide a short yet convincing justification for this one. Ian > > Cheers, > Bijan. > >
Received on Monday, 9 February 2009 10:54:23 UTC