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Chapter 11 Managing Knowledge 467

series of cases, and this knowledge base is continuously expanded and refined
by users. You’ll find case-based reasoning in diagnostic systems in medicine or
customer support where users can retrieve past cases whose characteristics are
similar to the new case. The system suggests a solution or diagnosis based on
the best-matching retrieved case.

FUZZY LOGIC SYSTEMS

Most people do not think in terms of traditional IF-THEN rules or precise num-
bers. Humans tend to categorize things imprecisely using rules for making
decisions that may have many shades of meaning. For example, a man or a
woman can be strong or intelligent. A company can be large, medium, or small in
size. Temperature can be hot, cold, cool, or warm. These categories represent a
range of values.
Fuzzy logic is a rule-based technology that can represent such imprecision
by creating rules that use approximate or subjective values. It can describe
a particular phenomenon or process linguistically and then represent that
description in a small number of flexible rules. Organizations can use fuzzy
logic to create software systems that capture tacit knowledge where there is
linguistic ambiguity.
Let’s look at the way fuzzy logic would represent various tempera-
tures in a computer application to control room temperature automatically.
The terms (known as membership functions) are imprecisely defined so
that, for example, in Figure 11.8, cool is between 45 degrees and 70 degrees,
although the temperature is most clearly cool between about 60 degrees
and 67 degrees. Note that cool is overlapped by cold or norm. To control the
room environment using this logic, the programmer would develop similarly
imprecise definitions for humidity and other factors, such as outdoor wind
and temperature. The rules might include one that says: “If the tempera-
ture is cool or cold and the humidity is low while the outdoor wind is high
and the outdoor temperature is low, raise the heat and humidity in the room.”

FIGURE 11.8 FUZZY LOGIC FOR TEMPERATURE CONTROL

The membership functions for the input called temperature are in the logic of the thermostat to control the room temperature. Membership
functions help translate linguistic expressions such as warm into numbers that the computer can manipulate.

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