> I'm afraid that adding existentials to rule heads pushes the language > outside of Horn. In fact, we would nearly have full first-order logic How so? You can just get rid of it by Skolemizing it. This is a typical N3 Rule, saying that for every two things with a grandparent relation, there exists a third thing connected to those things by a parent relation: { ?x :grandparent ?y. } => # read "[ ... ]" as "something which has ..." { ?x :parent [ :parent ?y ] }. I would turn that into this BLD: ?x[parent->sk1(?x,?y)] :- ?x[grandparent->?y] sk1(?x,?y)[parent->?z] :- ?x[grandparent->?y] The results to all positive ground queries on these two rule bases would be the same, wouldn't they? -- SandroReceived on Friday, 23 May 2008 14:19:39 UTC
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