Francois Bry wrote: > Dear All, > > The issue Jos has raised with his suggestion to include builtin > metapredicates like findall in the RIF condition language is, in my > opinion, that of grouping (and implicitely aggregation) in both SPARQL > and RIF. > > These are by no means sdimple issues, whatver examples might let think. > These are difficult semantics and evaluation issues, and also (often > neglected) language design issues. They are in my opinion as difficult > as nonmonotonic negation. yes, aggregates and grouping need some form of closing the world or scoping... for a good article defining the semantics of aggregates in LP style rules possibly involving even unstratified negation as failure and disjunctive rules, see: Wolfgang Faber, Nicola Leone, Gerald Pfeifer: Recursive Aggregates in Disjunctive Logic Programs: Semantics and Complexity. JELIA 2004: 200-212 (Remark for LP enthusiasts: This paper has a very elegant reformulation of the Gelfond-Lifschitz reduct for defining the stable model semantics generalized to programs with aggregates! ;-)) This is, to my knowledge, the most general semantics for aggregates in rules so far. axel > I feel a bit concerned that the RIF might include metapredicates like > findall in its condition language without these issues being properly > worked out - in RIF and SPARQL. > > Regards, > > Francois > > >>>>unifies ?ANSWER with a list that contains all the >>>>instantiations of ?SELECT satisfying the ?WHERE >>>>clause in the ?SCOPE of all asserted n3 formulae >>>>and their log:conclusion"""; >>>> a rdf:Property; >>>> rdfs:domain log:Formula; >>>> rdfs:range rdf:List. >>>> >>>>I mean useful for 2 reasons >>>>1/ it is a way to have a simple SPARQL condition >>>>2/ it is a way to have a SNAF condition when used as >>>> ?SCOPE e:findall (?SELECT ?WHERE rdf:nil). >>>> >>>>There is a test case result at >>>>http://eulersharp.sourceforge.net/2006/02swap/medicE.n3 >>>> >> >> > > > > > -- Dr. Axel Polleres email: axel@polleres.net url: http://www.polleres.net/Received on Tuesday, 19 September 2006 14:50:30 GMT
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