- From: Wagner, G.R. <G.R.Wagner@tm.tue.nl>
- Date: Thu, 11 Oct 2001 14:17:01 +0200
- To: "'tim finin'" <finin@cs.umbc.edu>
- Cc: www-rdf-rules@w3.org
> I always liked the example that was given in the KIF documentation > (KIF 3.0 Ref. Manual, > http://logic.stanford.edu/kif/Hypertext/node37.html): > > ... On the other hand, in some cases, replacing <<= by <= would be > semantically unacceptable. For instance, the rules > > (<<= (status-known ?x) (citizen ?x)) > (<<= (status-known ?x) (not (citizen ?x))) > > allow us to infer (status-known Joe) only if one of the sentences > > (citizen Joe), (not (citizen Joe)) > > can be inferred. Replacing the rules by implications would make > (status-known ?x) identically true." But according to classical (2-valued) logic, there is no difference here between the rules and the corresponding implications. The sentence (status-known Joe) could also be inferred from the two rules alone, since every classical (i.e. total and coherent) model of the two rules would satisfy it, simply because it would either satisfy (citizen Joe) or (not (citizen Joe)), and in both cases, as it satisfies both rules, it would also have to satisfy (status-known Joe). So, the author of this text on KIF seems to make a mistake here. In fact, he unintentionally describes the behavior of rules in extended logic programs where "not" corresponds to the strong (monotonic) negation of partial logic, where models are partial and the "tertium non datur" (= law of the excluded middle) does not hold. -Gerd --------------------------------------- Gerd Wagner http://tmitwww.tm.tue.nl/staff/gwagner/ Dep. Information & Technology Eindhoven University of Technology Email: G.Wagner@tm.tue.nl Phone: (+31 40) 247 26 17 Fax: (+31 40) 247 26 12
Received on Thursday, 11 October 2001 08:17:05 UTC