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From: ken@aiai.ed.ac.uk (Ken Johnson)
Newsgroups: comp.ai
Subject: Re: What is "fuzzy logic"?
Message-ID: <4412@skye.ed.ac.uk>
Date: 2 Apr 91 10:05:03 GMT
References: <13842@ccncsu.ColoState.EDU> <1991Mar29.195535.16601@watdragon.waterloo.edu> <2278@lee.SEAS.UCLA.EDU> <1991Apr1.205421.8079@athena.cs.uga.edu>
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In article <1991Apr1.205421.8079@athena.cs.uga.edu>
mcovingt@athena.cs.uga.edu (Michael A.  Covington) writes:

>In fuzzy logic, truth values range from 0 to 1. 

In some versions, truth varies from -1 to +1, with -1 meaning `certainly
false', +1 meaning `certainly true' and 0 meaning `don't know'.  E.g. 
``It is raining now in Los Angeles'' has a truth value of 0 (for me)
because I have no evidence one way or the other, but ``It is raining now
in Edinburgh'' has a truth value of -1 because I can see the sun
shining. 

The version implemented in the `Fril' language goes a step further, and
a truth value is indicated as a range.  E.g.  the truth value of some
statement might be written as (0.5 0.7) meaning that its certainty lies
somewhere between 0.5 and 0.7 inclusive. 

A probability can also be attached to a rule as a probability of
implication.  ``It is raining --> the sidewalk is wet'' has a certainty
of +1 since the sidewalk always gets wet when it rains, but ``It is
raining --> Louise is wet'' has a certainty of around 0.2 as Louise
doesn't usually go out in the rain. 



Ken Johnson, AIAI             This is the Earth. No-one gets out of here alive
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