From: Drew McDermott <drew.mcdermott@yale.edu>

Date: Fri, 12 Oct 2001 09:29:57 -0400 (EDT)

Message-Id: <200110121329.f9CDTvG27705@pantheon-po02.its.yale.edu>

To: www-rdf-rules@w3.org

Date: Fri, 12 Oct 2001 09:29:57 -0400 (EDT)

Message-Id: <200110121329.f9CDTvG27705@pantheon-po02.its.yale.edu>

To: www-rdf-rules@w3.org

[Gerd Wagner] Notice that we can associate a model-theoretic semantics with rules in a natural way: an interpretation I satisfies a rule (is a model of it) if it satisfies its consequent whenever it satisfies its antecedcent. > >The sentence (status-known Joe) could also be inferred from the > >two rules alone, > [Pat Hayes] > From the two implications, but not from the rules. In fact, strictly > speaking, nothing can be inferred *from* a rule, only *by* a rule. Yes, we can infer from a rule set: using the above definition of a model of a rule, we can define that a rule set R entails a sentence F if all models of R satisfy F (in logic programming we say that R entails F if all stable models of R satisfy F). You're assuming that a what a rule set entails by your definition is equivalent to what is inferrable. That is, you're assuming that the theory + rules is complete. But the sort of rule in question here gives rise to incompleteness for precisely the reasons you describe: '(status-known Joe)' is true in all models, but can't be inferred. This may be an argument against your proposed model-theoretic semantics for rules. -- Drew McDermottReceived on Friday, 12 October 2001 09:30:00 UTC

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