Re: Adding more evidence


Subject: Re: Adding more evidence
From: Will Dwinnell (predictor@compuserve.com)
Date: Thu Jan 20 2000 - 01:42:23 MET


Kami ROUSSEAU wrote:
"For my M.Sc. in computer science, my subject is the development of an
expert system. I wanted to use fuzzy logic, but my director said that fuzzy
rules do not take added evidence into account. Here is the exemple that he
gave me:
(assume that the AND operator is defined as "maximum")
IF outsideIsGreen AND insideIsRed THEN objectIsWatermelon

Suppose we only have 1 fact:
a certain fruit's outside is 60% green.
we can conclude that the fruit is a watermelon with possibility 60%

Suppose we add the following evidence:
the fruit's inside is red at 40%.
after recomputing the truth value of the rule, we still get 60%.

My director says that the possibility should have increased, but it did not,
so fuzzy logic is not appropriate for this kind of reasoning.

What do you think of his argument?"

It assumes very simplistic (and strange) rules. A fuzzy system like this
involves both rules and facts. His rules are obviously of the form "IF
antecedent is X true, THEN conclusion is X true". Besides, fuzzy logic is
not limited to min/max operators. See Earl Cox's first book on fuzzy logic
for a slew of alternatives.

Will Dwinnell
predictor@compuserve.com

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