Logic Layering Issues for DAML Rules

From: Sandro Hawke (sandro@w3.org)
Date: 03/08/03

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    We've talked about the DAML Rules language, like RuleML, having at
    least one of its concrete syntaxes be RDF-Graph-based like OWL.  This
    raises concerns over logic layering; we need to handle universally
    quantified variables and some forms of negation.  (An aside: when
    people say "Horn rules" are they thinking only definite clauses, or
    full Horn clauses, with headless rules, giving us classical negation?
    My understanding is that's not as widely implemented, but since I'm
    tempermentally inclined towards a full FOL syntax, I view it as a step
    in the right direction.)
    There were various comments about this at SWArch [1] yesterday, and I
    think I heard Pat and Ian say they knew how to do it, and maybe even
    saw Peter nod, but I didn't hear how.  When I've suggested doing it by
    encoding the syntactic structures of the rules into RDF and then using
    a limitted truth predicate (as in KIF [2]) to indicate which such
    structures are intended to be asserted as rules, people start to look
    very concerned.  
    In any case, do we have a solution at hand, or is this going to be a
    major obstacle?
       -- sandro
    [1] http://www.w3.org/2001/sw/meetings/tech-200303/
    [2] As far as I can tell from the record, KIF had a strong
        Perlis-style truth predicate called 'true' [3] until it
        was deemed unnecessarily complicated to implement [4]
        and replaced by a two-level predicate, 'wtr' [5]. 
    [3] http://meta2.stanford.edu/kif/Hypertext/node35.html
    [4] http://logic.stanford.edu/kif/decisions.html
    [5] http://logic.stanford.edu/kif/dpans.html#10.3

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