Classification rules represent knowledge in the form of logical if-else statements that assign a class to unlabeled examples. They are specified in terms of an antecedent and a consequent; these form a hypothesis stating that "if this happens, then that happens." A simple rule might state, "if the hard drive is making a clicking sound, then it is about to fail." The antecedent comprises certain combinations of feature values, while the consequent specifies the class value to assign when the rule's conditions are met.
Rule learners are often used in a manner similar to decision tree learners. Like decision trees, they can be used for applications that generate knowledge for future action, such as: