- From: Gary Hallmark <gary.hallmark@oracle.com>
- Date: Wed, 27 Jun 2007 15:24:45 -0700
- To: public-rif-wg@w3.org
Axel Polleres wrote: > As for adding (locally) stratified negation to horn, I can say that > ignoring rules with stratified negation would simply give you > incomplete models, but all > inferred atoms would still be sound. > If I understood correctly, Sandro was with his nnotion of "impact" > talking about different treatments of "fallback", e.g. something like > (this probably only applies to deductive rules though): > > a) ignoring X will lead to sound inferences only but inferences > might be incomplete > b) ignoring Y will lead preserve completeness but unsound inferences > might arise > c) ignoring z will neither preserve soundness nor completeness > > etc. > while the latter two are probvably pointless, I could well imagine use > cases for a) e.g. when doing query answering over a rule base > I might be happy to get sound answers but not requiring all answers > > example: > > p(a) <- p(b). > p(b). > q(c). > r(d). > > p(X) <- not q(X). > > When I now ask for > p(X). > > I'd get p(a) and p(b) in all cases even if I ignore the last rule. > p(c) would only get inferred when having the last rule. actually you'll get p(a) twice rather than p(c). But I see your point. My points are 1. you need quite a bit of detail in the fallback mechanism to know that not handling "not" must fallback to ignoring the containing *rule*. Just ignoring the *term* containing "not" would be very bad. 2. this fallback doesn't work in the presence of some extensions (like classical negation) and would be ill-advised (though technically sound, I guess) in the presence of "world-closing" extensions like aggregation -- Oracle <http://www.oracle.com> Gary Hallmark | Architect | +1.503.525.8043 Oracle Server Technologies 1211 SW 5th Avenue, Suite 800 Portland, OR 97204
Received on Wednesday, 27 June 2007 22:25:08 UTC