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Re: Rules WG -- draft charter -- NAF

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Thu, 13 Nov 2003 11:47:37 -0500 (EST)
Message-Id: <200311131647.hADGlbu28480@pantheon-po04.its.yale.edu>
To: www-rdf-rules@w3.org


   [Sandro Hawke]
   But... Well, at very least that's non-monotonic.
   ...

   So what can you do?  W3C SWAD (mostly TimBL) has been looking at this
   for a while, and Cwm implements two solutions via built-ins [2]:

       log:includes + log:notIncludes statements depend on whether some
       web-accessible RDF graph includes some subgraph.  This lets you
       say the game has no errors if http://foo.bar doesn't list any
       errors.

       log:definitiveDocument approaches this from the other side,
       letting you say http://foo.bar lists all "errors", by the very
       definition of "errors".   An exported SQL database with usual
       closed-world semantics can simply include that it's a
       log:definitiveDocument for all its predicates/columns, and the
       expected NAF-like behavior should ensue.

These are excellent ideas.  I just want to call attention to the fact
that you're saying:

  Solution X to a problem is nonmonotonic ("at least," meaning it may
  have even worse problems).  "What can you do?"  "Two solutions: "
  <good idea 1> <good idea 2>

But the two good ideas are _also_ nonmonotonic.  An addition to the
contents of the files being pointed at might cause an inference to go
from drawable to undrawable.  Pat Hayes has a phrase to describe the
situation, something like "locally nonmonotonic," or "locally closed
world." 

My point is that NAF and other forms of nonmonotonicity are
indispensable.  It's good to look for ways to control them, but bad
practice to use "nonmonotonic" as a general term of opprobrium,
because it leads the casual reader to assume that nonmonotonicity is
the root of the problem.

                                             -- Drew


-- 
                                             -- Drew McDermott
                                                Yale University CS Dept.
Received on Thursday, 13 November 2003 11:47:38 UTC

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