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comments on RIF-BLD and RIF-PRD

From: <rak@doc.ic.ac.uk>
Date: Thu, 9 Oct 2008 14:38:58 +0100 (BST)
To: public-rif-comments@w3.org
cc: rak@doc.ic.ac.uk
Message-ID: <alpine.DEB.2.00.0810091438580.1458@pintail.doc.ic.ac.uk>

I have skimmed several of the RIF documents and am disappointed, but not
surprised, to see how little has been done to relate and reconcile the Horn
clause and the production rule languages, RIF-BLD and RIF-PRD respectively.
In particular, both documents, as far as I can tell, ignore the fact that
one of the main practical uses of both Horn clauses and production rules is
to reduce goals to sub-goals.

The RIF-BLD document does not address the operational semantics of Horn
clauses, nor their intended use for knowledge representation. Nor does the
operational semantics of RIF-PRD deal with the use of production rules for
goal-reduction.

Arguably, in practice, there are three kinds of production rules: reactive
rules, which are event-condition-action rules; forward chaining logic rules,
which derive conclusions from conditions; and goal-reduction rules, which
simulate backward chaining while doing forward chaining. The operational
semantics of the RIF-PRD document caters for the first two kinds of rules,
but not the third. In particular, it restricts the relationship with RIF-BLD
to the second kind of rule, forward chaining with logic rules.

The general confusion in the AI literature about these matters is reflected
in confusion about the meaning of conditionals in the psychology of
reasoning literature. I discuss these confusions and propose a solution in a
recent paper, "Reasoning with Conditionals in Artificial Intelligence"
(http://www.doc.ic.ac.uk/~rak/papers/conditionals.pdf).

The proposed solution provides both a logical and operational semantics for
a framework that integrates logic programs and production rules. Although
the framework is presented as an extension of logic programming, it can also
be viewed operationally as a production rule system that uses logic programs
both to evaluate conditions of production rules and to reduce "actions" that
are goals to sub-goals.
Received on Thursday, 9 October 2008 14:14:54 GMT

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