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

From: tim finin <finin@cs.umbc.edu>
Date: Fri, 05 Oct 2001 10:33:26 -0400
Message-ID: <3BBDC4B6.66C1D0A@cs.umbc.edu>
To: www-rdf-rules@w3.org
CC: Drew McDermott <drew.mcdermott@yale.edu>
Drew McDermott wrote:
> ...
>  >  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. 
> ...
> Gerd provided a lot of useful examples as well, although perhaps he
> too faithfully obeyed the principle of latino gullibilum impressis.

I always liked the example that was given in the KIF documentation 
(KIF 3.0 Ref. Manual, http://logic.stanford.edu/kif/Hypertext/node37.html):

"The rationale for using monotonic rules in knowledge representation, 
instead of implications, is twofold. On the one hand, the ``directed'' 
character of rules can simplify the task of developing efficient inference 
procedures. On the other hand, in some cases, replacing <<= by <= would be 
semantically unacceptable. For instance, the rules

  (<<= (status-known ?x) (citizen ?x))
  (<<= (status-known ?x) (not (citizen ?x)))

allow us to infer (status-known Joe) only if one of the sentences 

  (citizen Joe),  (not (citizen Joe))

can be inferred. Replacing the rules by implications would make 
(status-known ?x) identically true."
Received on Friday, 5 October 2001 10:23:43 UTC

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