- From: Enrico Franconi <franconi@inf.unibz.it>
- Date: Thu, 12 Jan 2006 11:56:38 +0100
- To: Jos de Bruijn <jos.debruijn@deri.org>
- Cc: public-rif-wg@w3.org
On 12 Jan 2006, at 11:46, Jos de Bruijn wrote: >>> Wrt. the existential information: the semantics of LP rules is >>> based on >>> Herbrand models, which means (among other things) that every >>> individual >>> in the universe is represented with a name in the language. This >>> makes >>> it impossible to truly capture existential information. >> >> I disagree. For example, In Rosati's approach non-distinguished >> varibales (i.e., existentials) are not restricted to the herbrand >> universe. BTW all the use cases in Managing Incomplete Information >> <http://www.w3.org/2005/rules/wg/wiki/ >> Managing_incomplete_information> would be correctly handled by >> Rosati's approach. > > Rosati uses the standard names assumption, which excludes considering > unnamed individuals, thus, certain kinds of existential knowledge > cannot > be captured in his approach. As in none LP based approaches. > If you have a name for the individual, then you can certainly deal > with > it in the logic program. > However, if we would take the following example: > > take the following first-order sentence: > \exists x. p(x) > > and the following rule: > > r <- p(x) > > One cannot conclude r, because there is no name a such that p(a). In Eiter, the above rule would not derive r, and in Rosati it couldn't even be written since it is not DL-safe. You could automatically make it DL-safe, and then you wouldn't derive r either. However, unlike Eiter, and unlike pure LP based approaches, in his recent work Rosati does allow for several kind of classical existentials. For example, the use cases involving OWL-Lite in <http://www.w3.org/2005/rules/wg/wiki/ Managing_incomplete_information> would be captured correctly by Rosati but not by Eiter. cheers --e.
Received on Thursday, 12 January 2006 10:57:00 UTC