- From: Christian de Sainte Marie <csma@ilog.fr>
- Date: Tue, 30 Aug 2005 20:50:38 +0200
- To: Michael Kifer <kifer@cs.sunysb.edu>
- CC: Dan Connolly <connolly@w3.org>, public-rule-workshop-discuss@w3.org
Michael Kifer wrote: > > There was a set S (I am changing the name to avoid confusion with the above > symbol A): > > 2 rules, one with a SNAF > several facts > > There was a conclusion F, such that > > S |= F. > > Note: |= here is NOT due to modus ponens! > > There was also a set B of facts (just 1 fact), such that > > S + B |/=F Could it be that the misunderstanding comes from how you think of the CWA? (Forgive me if I misuse formal notation below: I hope that the intended meaning remains clear) If you think of CWA as an inference rule (like modus ponens), you get CWA: rule with SNAF and several facts |= some negated facts {~Fi} Modus Ponens: other rule and several facts + {~Fi} |= F So that, really, S |= {~Fi} + F Now, if you add {Fi} to S, you cannot infer {~Fi] anymore, and without them, you cannot infer F anymore: S + {Fi} |\= F Now, if you think of CWA as a property of the world (to be closed, I mean) for which SNAF is an indicator, then S really is: 2 rules, one with classical negation (you do not need SNAF anymore once you make everything explicit) several facts {~Fi} then, you have Modus Ponens: S |= F but you do not have S + {Fi} |\= F, because S + {Fi} is inconsistent. I do not claim that the second interpretation is correct: I just wonder whether this is not what Dan really had in mind when he challenged your addition of OO7car being yellow in S to prove nonmonotonicity? At least, I believe this is what I had in mind when I introduced the farfeluesque notion of "bounded monotonicity": in the same way like you need not take into account facts out of the scope of my SNAF if you need only reason within that closed world (and thus you do not need nonmonotonic inference), you can safely reason monotonically if you know that you stay within the bounds where your world is monotonic (yes, this look a lot like a definition of nonmonotonicity, but it is not, really: if I am born, do queries and draw inferences from a database and then die before any change affects that DB - within the bounds of that DB monotonicity -, then, for all practical purposes, that DB is monotonic, as far as I am concerned). Once again, I am not trying to say that bounded monotonicity makes sense or whatever. I am just wondering if we would not all agree that we need not care about nonmonotonicity as long as the interchange language provides a way to make clear the scope (of NAF, and of other nonmonotonicity-generating operations, if there are any and they are required): the applications that want to use the retrieved rules have to care about it, if they want to reason outside that scope. And, yes: I am perfectly aware that, maybe, none of this makes sense :-) Christian
Received on Tuesday, 30 August 2005 18:49:38 UTC