From: Dan Connolly <connolly@w3.org>

Date: Fri, 26 Aug 2005 17:51:31 -0500

To: Michael Kifer <kifer@cs.sunysb.edu>

Cc: doug.foxvog@deri.org, public-rule-workshop-discuss@w3.org

Message-Id: <1125096691.16011.157.camel@dirk>

Date: Fri, 26 Aug 2005 17:51:31 -0500

To: Michael Kifer <kifer@cs.sunysb.edu>

Cc: doug.foxvog@deri.org, public-rule-workshop-discuss@w3.org

Message-Id: <1125096691.16011.157.camel@dirk>

On Fri, 2005-08-26 at 12:57 -0400, Michael Kifer wrote: [...] > > If @ is merely a namespace identifier, it wouldn't be a reference to a > > set, merely a method of abbreviation. It seems unlikely to me that N3 > > fixes in stone any namespace as soon as an "@" sign is used to indicate > > it. Again, with the caveat that i don't know N3, it seems that Michael > > is correct, and adding the formula B does not "change what @allAboutCars > > denotes". > > No, I think Dan and I mean the same thing, Well, up to a point. But evidently F-Logic and N3 work differently in this regard. > but uses the words "set" and > "bunch" informally. I think Dan was confused as to what "inference" means > in nonmonotonic logics (judging by his remark that I was using two different > interpretations for the set of formulas A). I was confused about how F-Logic works. I'm still studying the @ construct in F-Logic, but it doesn't seem to be analagous to log:includes/log:notIncludes after all. Leaving N3 aside, perhaps I can show what I mean by monotonic SNAF using KIF, i.e. ordinary first-order logic plus quoting. Consider a relation on (quoted) formulas: (simply-entails F1 F2) where F1 and F2 are (quoted) KIF expressions that are analagous to RDF graphs/formulas, i.e. they look like (exists (b1 b2 b3 ...) (and (holds p1 s1 o1) (holds p2 s1 o2) ... ) ) or in the case of no existentials, just (and (holds p1 s1 o1) (holds p2 s1 o2) ... ) or in the case of just one conjunct, just (holds p1 s1 o1) and simply-entails is defined as per section 7.1 Simple Entailment Rules of RDF Semantics http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#dt-simple-entailment That is the formula F2 can be obtained from F1 by some combination of erasure... (simply-entails '(and (holds price book1 10) (holds title book1 "abc")) '(holds price book1 10) ) and existential introduction: (simply-entails '(holds location fred texas) '(exists (?somewhere) (holds location fred ?somewhere)) and variable renaming, and re-ordering the conjuncts in an and. I'm glossing over the fact that "location" isn't quite a URI for clarity. Strictly speaking, it would be something like http\:\/\/example\/vocab\#location . This simply-entails relation is clearly an ordinary computable relation, just like string matching or testing whether one number is a factor of another. (It's called "graph match" in any number of RDF implementations). Then consider simply-entails-c , the complement of simply-entails. It's also computable: compute simply-entails and negate it. Also, let (lookup SYMBOL) be some function that takes a (quoted) symbol and returns some formula expression. Now I can write my rule about car color defaults as: (=> (simply-entails-c (lookup 'car-specification) '(exists (?v) (holds auto-color car ?v)) ) (holds auto-color car black) ) The (lookup 'car-specification) term denotes some expression in each interpretation; either that expression does simply-entail '(exists (?v) (holds auto-color car ?v)) or it doesn't. To "add another statement" to the formula expression we get when we look up 'car-specification is to consider a different interpretation of the lookup function. Let A be (simply-entails-c (lookup 'car-specification) '(exists (?v) (holds auto-color car ?v)) and F be (holds auto-color car black) Then clearly we have Forall B A |= F implies A union B |= F right? -- Dan Connolly, W3C http://www.w3.org/People/Connolly/ D3C2 887B 0F92 6005 C541 0875 0F91 96DE 6E52 C29EReceived on Friday, 26 August 2005 22:51:37 GMT

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