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From: creelman@dalcsug.UUCP (Paul Creelman)
Newsgroups: comp.ai.digest
Subject: Uncertainty and FUZZY LOGIC VS PROBABILITY
Message-ID: <8802291913.AA13911@dalcsug.UUCP>
Date: 29 Feb 88 19:13:18 GMT
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: Dalhousie University, Halifax, N.S., Canada
Lines: 41
Keywords: Uncertainty,probability
Approved: ailist@kl.sri.com


Subject: Uncertainty and FUZZY LOGIC VS PROBABILITY
Newsgroups: comp.ai.digest
Keywords: UNCERTAINTY, PROBABILITY

   There appears to be some discussion about uncertainty by Eric Neufeld
   and others. According to Spiegelhalter, the use of probability for
   representing uncertainty in expert systems is the wrong method. He says
   it  is inappropriate because uncertainty in knowledge does not match the
   chance mechanism of an observable event. It is unnecessary since no meaning
   must be attached to numbers, but instead the rank order of hypotheses is 
   often all that matters in an expert system. Furthermore probability is
   somewhat impractical since it requires too many estimates of prior
   probabilities, fails to distinguish ignorance from uncertainty, and
   fails to provide an explanation of conclusions. I must agree. Down with
   probability!
   Surely what is needed is a simplified version of Shafer's evidence theory
   which deals with all possible subsets of the possible variable values, the
   frame of discernment. A number is associated with each subset which measures
   the certainty that the actual variable value is in that subset. Suppose we
   coarsen the uncertainty measure by reducing the number of subsets specified.
   While providing a measure of certainty for all subsets of values may be
   impractical, a system that uses only a limited number of these subsets
   could be very useful. If only there was a way of consistently updating 
   certainty for such subsets! I wonder if additivity of the certainty measure
   is necessary. Perhaps a condition like c(B)> c(C) -> c(A+B) > c(A+C) where
   A B and C are disjoint subsets and + is set union. Of course, it is desirable
   to allow A B and C to have common elements as well. I hope this will 
   stimulate discussion. For references, see
   William Gale,ed.,Artificial Intelligence and Statistics, Addison-Wesley
   Publishing Company,1986.

   L.N.Kanal,J.F.Lemmer,eds.,Uncertainty in Artificial Intelligence,
   North-Holland,1986. 


   Paul Creelman
   student
   Dalhousie University


   ZZ