3.4 divide-and-Conquer approaCh 99
The algorithm is fast and efficient, but not as accurate as a decision tree.
The accuracies of predicting classes for unseen instances using existing rules
can be improved through a global optimization step on the rule set by revis-
ing and replacing individual rules with the method introduced in RIPPER.
RIPPER slightly modifies the strategy used in REP and IREP to form
and prune individual rules. In addition, RIPPER adds an additional opti-
mization step to improve the prediction accuracy of the rule set by revising,
deleting, or replacing the pruned rules. During the optimization process, for
each rule produced from IREP, two alternative rules are constructed: (1) a
replacement rule and (2) a revision r