- From: Bijan Parsia <bparsia@cs.man.ac.uk>
- Date: Mon, 5 Mar 2007 15:28:31 +0000
- To: Matt Williams <matthew.williams@cancer.org.uk>
- Cc: Semantic Web <semantic-web@w3.org>
On 5 Mar 2007, at 15:13, Matt Williams wrote: > Dear Bijan, > > Thanks a lot - very helpful, as usual. > > The approach with nominals is interesting - I'll have a play and > see what happens. > > I guess what I missed from my first question is that if: > > \exists hasRole.\top > > is a valid class expression It is. > (which I think it is) then: > > ¬(\exists hasRole.\top) > should be valid. It is too. But this says the same thing as: \forall hasRole \neg\top or \forall hasRole \bot Which means if I am an instance of this class I hasRole to *nothing*, that is, I have no such roles at all. This is a bit different that "bob doesn't love mary". I.e., in order to say "bob doesn't love mary" you have to say that bob doesn't love *anyone*. Poor bob! > But since adding \top to the formula doesn't seem to add anything, > could one write ¬(\exists hasRole) as a shorthand? I think the > answer is no, but I'm not clear why. The shorthand is fine if it implies the above. Indeed, think of unqualified number restrictions which could be equivalently written via qualified number restrictions and top. It might help to do the standard translation into FOL which will show you exactly how the variables are working. Cheers, Bijan.
Received on Monday, 5 March 2007 15:28:30 UTC