Model Answer for Assignment 2
1
Step 1:
Find all the confident rules for a given minimum confidence. ( Given a
minimum confidence minconf, a rule is confident if conf(
x→c
)
≧ minconf, where
conf(
x→c
) is the confidence of rule
x→c
)
Step 2:
From association rules to a classifier
Let C denote the set of condent rules plus the default rule,
Ø
→
c, where c is the
majority class in relational table T. Let size(r) denote the number of values
in rule r, and let lhs(r) denote the lefthand side of r. We assume that the values in a
rule are ordered lexicographically. Similarly, rules can be ordered lexicographically.
For example, rule x,y
→
1 precedes rule y
→
0 lexicographically.
Binary relations:
Consider two rules r and r’ in C. We say that r is ranked higher than
r’ written as r
r’, if the following conditions hold: conf(r) > conf(r’); or if conf(r) =
conf(r’), but sup(r) > sup(r’); or if sup(r) = sup(r’), but size(r) < size(r’); or if size(r) =
size(r’), but r precedes r’ in the lexicographical order of rules. We say that r is more
general than r’ (or r’ is more special than r), written r
’, if lhs(r)
lhs(r’).
R
p
G
p
r
⊆
CF Principle:
If there are choices, the rule of the highest rank has the priority.
e can use the MCF principle to resolve the conflict in covering a case: the covering
edundant rules: Arule r in C is redundant if there is some rule r’ in C that is more
ith only nonredundant rules, we can show that lefthand sides of rules are distinct,
tep 3:
Pruning the Classifier
, the MCF principle implies that the highest ranked
d
DT:
Consider a nondefault rule r in C. The parent of r is the rule in C that is more
M
W
rule of a given case is the rule that matches the case and has the highest possible rank.
R
general and ranked higher than r, that is, r’
p
r and r’
p
r
G
R
W
and thus, that the generalization relationship is a lattice over lefthand sides of rules.
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 Fall '09
 AdaFu

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