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

Date: Fri, 26 Aug 2005 14:10:13 -0400

To: jos.deroo@agfa.com

Cc: Dan Connolly <connolly@w3.org>, public-rule-workshop-discuss@w3.org, public-rule-workshop-discuss-request@w3.org

Message-Id: <20050826181013.C9750CB5D3@kiferserv.kiferhome.com>

Date: Fri, 26 Aug 2005 14:10:13 -0400

To: jos.deroo@agfa.com

Cc: Dan Connolly <connolly@w3.org>, public-rule-workshop-discuss@w3.org, public-rule-workshop-discuss-request@w3.org

Message-Id: <20050826181013.C9750CB5D3@kiferserv.kiferhome.com>

jos.deroo@agfa.com wrote: > > >>> Michael Kifer wrote: > >>> Dan Connolly wrote: > >>>> On Aug 24, 2005, at 8:11 PM, Michael Kifer wrote: > >>>>> [...] > >>>>> No, you got me wrong. I do believe that nonmonotonicity is > >>>>> important, but you already have it in the form of SNAF. > >>>> > >>>> I'm having trouble understanding that. I see it shows up in > >>>> several of your recent messages, e.g. > >>>> > >>>> "SNAF is nonmonotonic." > >>>> http://lists.w3.org/Archives/Public/public-rule-workshop-discuss/2005Aug/0029.html > >>>> > >>>> My understanding is that SNAF is monotonic. > >>>> > >>>> Earlier[1] we discussed this example rule... > >>>> > >>>> { :car.auto:specification log:notIncludes {:car auto:color []}} > >>>> => {:car auto:color auto:black}. > >>>> > >>>> That rule is monotonic; if the antecedent is true, the > >>>> consequent remains true regardless of how many other > >>>> things are also true. > >>> > >>> Hi Dan, > >>> Welcome to the discussion! Yes, it is very important to > >>> get to the bottom of it so that everybody will start > >>> speaking the same language. > >>> > >>> No, the above rule is nonmonotonic. If you add a color > >>> specification to that car then :car.auto:specification > >>> will now include a color specification and log:notIncludes > >>> will become false. Therefore > >>> :car auto:color auto:black > >>> will no longer be derived. > >> > >> I'm aware of following sentence from > >> http://www.w3.org/2000/10/swap/doc/Reach > >> > >> [[ > >> Also, if we start to just loosely talk about defaults in > >> the sense of "if you don't already know a color", then > >> different agents will end up drawing different conclusions > >> from the same data, which is not a good foundation for a > >> scalable web. > >> ]] > >> > >> and believe that > >> > >> <uri-of-document> log:semantics ?F. > >> ?F log:notIncludes {set-of-triples}. > >> > >> is a robust approach and is monotonic > >> (you cannot add things to ?F) > > > > Jos, > > > > Monotonicity or nonmonotonicity is a property of a logical > > language, not of a particular set of formulas. > > Okay > > > Furthermore, in your example, ?F is just a variable whose > > quantification you neglected to specify. > > Well, I should have said that the triples > > <uri-of-document> log:semantics ?F. > ?F log:notIncludes {set-of-triples}. > > were in the premise of a N3 rule and then ?F is a > universally quantified variable with the scope of > that rule. OK. You wrote them as if they were facts, so I was confused. > > A proper thing to do here would be to write something like: > > > > <uri-of-document> log:semantics t. > > t log:notIncludes {set-of-triples}. > > > > where t is a term that represents (reifies) the set of > > formulas that are encoded in uri-of-document. Now, t is > > a term, not a formula, so your statement about "adding > > things to ?F" is irrelevant as far as monotonicity > > of the language is concerned. > > Well, this is indeed where we seem to have a disconnect.. > I meant that for the set triples represented by ?F (and > which are real triples in my machine) there is no way to > add triples to that set; you can of course add triples to > the document at <uri-of-document> on the web but then, > formula A in your (**) has a different interpretation. No, this is where you get confused. See my earlier message adding to Dieter's tutorial on nonmonotonicity: http://lists.w3.org/Archives/Public/public-rule-workshop-discuss/2005Aug/0082.html The set of formulas A stays the same. The formulas that would be added to the document at <uri-of-document> form the set B. So, initially, "the document at <uri-of-document>" consists of the set A, and you get one set of inferences from there. Then "the document at <uri-of-document>" is changed to consist of the set of formulas A union B, and now you get a different set of inferences. I went again through Dan's example in the above message and explained once more why SNAF is nonmonotonic. Your query ?- <uri-of-document> log:semantics ?F and ?F log:notIncludes {set-of-triples}. is handled exactly the same (actually simpler) than Dan's car example. --michaelReceived on Friday, 26 August 2005 18:10:24 UTC

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