From: <jos.deroo@agfa.com>

Date: Thu, 25 Aug 2005 12:19:13 +0200

To: kifer@cs.sunysb.edu

Cc: public-rule-workshop-discuss@w3.org

Message-ID: <OF38699A27.DDB70733-ONC1257068.0037789E-C1257068.0038A99D@agfa.com>

Date: Thu, 25 Aug 2005 12:19:13 +0200

To: kifer@cs.sunysb.edu

Cc: public-rule-workshop-discuss@w3.org

Message-ID: <OF38699A27.DDB70733-ONC1257068.0037789E-C1257068.0038A99D@agfa.com>

>>>> [...] >> >> >> >>> Allow me to set things straight please. The inference rules >> >>> that are often (incorrectly) referred to as NAF ***always*** >> >>> have scope. I am not familiar with any notion of NAF that >> >>> doesn't refer to a scope. Typically the scope is IMPLICIT, >> >>> but it is ALWAYS WELL DEFINED. So, NAF is a form of SNAF >> >>> where the scope is defined implicitly, but always rigorously. >> >>> All Prolog systems that I am aware of are like that. >> >> >> >> Suppose that in my Prolog program I use lots of consult of >> >> resources on the web and also lots of assert and retract all >> >> conditioned by the state of the web, then how can you possibly >> >> say that that scope in which I'm deriving evidence while using >> >> negation as failure is ALWAYS WELL DEFINED?? >> > >> > At any moment when NAF is computed the set of rules and facts >> > is known to the inference engine. What is your problem? >> >> It is indeed known internally to the engine, no doubt. >> Would like to see that "ALWAYS WELL DEFINED" *outside* >> the engine to support "proof supporting a conclusion". > > First, what you are talking about is way ahead of what W3C > has in mind. Knowledge base dynamics is not even on the > horizon as far as the current discussion is concerned. > > Second, what do you mean by "well defined outside the engine"? > If your KB is dynamic then you can still provide explanations > to proofs (if this is what you meant), but such things become > more difficult, of course. Yes, this is what I meant; agree now with your "well-defined" I'm indeed not enough familiar with all literature and I will try to catch up as much as possible :) (I did Prolog in mid 80's and now again since last 5 years but have a gap between 90 and 00) > If you want to determine the state of a dynamic KB at a > particular point of execution ahead of time then it is > undecidable for reasonably expressive languages (recursion > is all you need for that). thanks -- Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/Received on Thursday, 25 August 2005 10:19:44 UTC

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