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From: jair-ed@ptolemy.arc.nasa.gov
Subject: New Article, Translating between Horn Representations ...
Message-ID: <1995Dec6.233849.28253@ptolemy-ethernet.arc.nasa.gov>
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Date: Wed, 6 Dec 1995 23:38:49 GMT
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JAIR is pleased to announce the publication of the following article:

Khardon, R. (1995)
  "Translating between Horn Representations and their Characteristic Models", 
   Volume 3, pages 349-372.
   PostScript: volume3/khardon95a.ps (284K)
	       compressed, volume3/khardon95a.ps.Z (114K)


   Abstract: Characteristic models are an alternative, model based,
   representation for Horn expressions. It has been shown that these two
   representations are incomparable and each has its advantages over the
   other. It is therefore natural to ask what is the cost of translating,
   back and forth, between these representations. Interestingly, the same
   translation questions arise in database theory, where it has
   applications to the design of relational databases. This paper studies
   the computational complexity of these problems.
   
   Our main result is that the two translation problems are equivalent under
   polynomial reductions, and that they are equivalent to the corresponding
   decision problem. Namely, translating is equivalent to deciding whether a
   given set of models is the set of characteristic models for a given Horn
   expression. 
   
   We also relate these problems to the hypergraph transversal problem, a
   well known problem which is related to other applications in AI and for
   which no polynomial time algorithm is known. It is shown that in general
   our translation problems are at least as hard as the hypergraph
   transversal problem, and in a special case they are equivalent to it. 

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