3.4 divide-and-Conquer approaCh 111
degrade the performance of the rule under a certain confidence level.
Therefore, the deletion of the condition will be finalized.
Now let’s consider the complexity of multiple conditions in a rule. If
the number of conditions in a rule is N, there are N ! possible combina-
tions of the conditions. If we carry out an exhaustive search on all possible
conjunctions of the conditions to determine whether to accept or reject
the temporary rule, it takes N ! number of tests for the single rule. For
a large database, the number of possible tests will become very huge. In
C4.5, Quinlan used a “greedy” approach to delete the conditions, which
produces reasonably accurate rules and is much faster than the exhaus- ...