In a rule induction method, an overbroad candidate rule is selected for categorizing a node to be categorized. The candidate rule is specialized by: (i) adding a rule node corresponding to a node level of structured training examples; (ii) including in a rule node a rule pertaining to an attribute of at least one node of the corresponding node level to produce a specialized candidate rule; and (iii) evaluating the specialized candidate rule respective to the structured training examples.