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Re: Expressiveness of RDF as Rule Conclusion Language (was Re: W hat is an RDF Query? )

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Fri, 5 Oct 2001 09:57:46 -0400 (EDT)
Message-Id: <200110051357.f95DvkG12075@pantheon-po02.its.yale.edu>
To: www-rdf-rules@w3.org

   [Sandro Hawke]
   Can we work in both directions at the same time?   I imagine both
   inference rules and implications being useful, perhaps in somewhat
   different application spaces.

   I don't exactly understand the difference, myself.  I appreciated
   Gerd's comment above, because it validated by own confusion over which
   way to understand a logic program.  I think n3 logic [1] [2] shows the
   same confusion.  The syntax and terminology ("log:implies") suggest
   implication, but its usage in forward chaining by the implementation
   (cwm) sounds like inference rules.  (cwm actually will infer new rules
   and use them.  What does that sound like?)

   Can someone give me a test case which shows where the difference is?

The simplest case is this one: If P->Q is an implication, then it
enables you to infer not-P from not-Q.  If it is an inference rule, it
allows you to infer Q from P, period.  

As Gerd pointed out, this raises the issue of whether the language
includes negation.  If it doesn't, then the usual equivalence of
'P->Q' and '(not P) or Q' goes away, and I'm not sure what implication
means any more.

Gerd provided a lot of useful examples as well, although perhaps he
too faithfully obeyed the principle of latino gullibilum impressis.

                                             -- Drew McDermott
Received on Friday, 5 October 2001 09:57:50 GMT

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