Database Reference
In-Depth Information
Combined Rule:
a rule for which the condition was the conjunction of all
conditions for rules in the set of most general rules.
Default Rule:
a rule with the antecedent
true
.
For all rules, the class was set to the class with the greatest number of in-
stances covered by the initial rule. All rules other than the default rule covered
exactly the same training cases. Hence all rules other than the default rule had
identical empirical support.
We present an example to illustrate these concepts. We utilize a two dimen-
sional instance space, defined by two attributes, A and B, and populated by
training examples belonging to two classes denoted by the shapes
.This
is illustrated in Fig. 1. Fig. 1(a) presents the hypothetical initial rule, derived
from some external source. Fig. 1(b) shows the most specific rule, the rule that
most tightly bounds the cases covered by the initial rule. Note that while we have
presented the initial rule as covering only cases of a single class, when developing
the rules at differing levels of generality we do not consider class information.
Fig. 1(c) and (d) shows the two most general rules that can be formed by deleting
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B
B
B
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4
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2468 0
A
2468 0
A
2468 0
A
a) Initial rule:
IF A ≤
6
∧
3
≤ B ≤
7
THEN •
b) Most specific rule:
IF
3
≤ A ≤
5
∧
4
≤ B ≤
6
THEN •
c) Most General Rule 1:
IF
4
≤ B ≤
6
THEN•
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B
B
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4
4
2
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2468 0
A
2468 0
A
d) Most General Rule 2:
IF A ≤
5
THEN •
e) Combined Rule:
IF A ≤
5
∧
4
≤ B ≤
6
THEN •
Fig. 1.
Types of rule generated
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