- From: Enrico Franconi <franconi@cs.man.ac.uk>
- Date: Fri, 11 May 2001 13:10:22 +0100
- To: www-rdf-logic@w3.org
On May 11, Sigfrid Lundberg, Lub NetLab writes: > I think that the problem here boils down to the wish to be able to > say things, and the wish to be able to infer things. I want to be > able to say that a sub-title is a subclassof title, and that there > should be no doubt whatsoever that all titles are not > sub-titles. Just some titles are. > > Some time ago, I was convinced by you (and other kind people on this > list) that we do need a not-strict-sub-class-of. The cost of making > certain inferences be would far too high if we didn't. So I accept > this... But I'm not comfortable with it; aren't we trading > inferability against expressiveness? Aren't we enhancing the former > at the price of the latter. To put this in another way: Could the > ability to say (i.e., in rdf/daml) that sub-titles "<" titles rather > than just that sub-titles "<=" titles make a more solid ground for > inference. I mean, some statements could actually be more > precise... I'd reckon that we need both. If you have a propositionally closed representation language, then having a not-strict-sub-class-of allows you to have the strict-sub-class-of as well. So there is NO trading inferability against expressiveness. This is how you could represent your example: Introduce first a freshly new primitive class "non-sub-title". Add the following axioms: sub-title is-a-not-strict-sub-class-of title. title is-a-not-strict-sub-class-of (sub-title or non-sub-title). non-sub-title is-a-not-strict-sub-class-of ((not sub-title) and title). This implies: sub-title is-a-strict-sub-class-of title cheers -- e. Enrico Franconi - franconi@cs.man.ac.uk University of Manchester - http://www.cs.man.ac.uk/~franconi/ Department of Computer Science - Phone: +44 (161) 275 6170 Manchester M13 9PL, UK - Fax: +44 (161) 275 6204
Received on Friday, 11 May 2001 08:10:35 UTC