1. A non-transitory computer-readable storage medium having instructions stored thereon, the instructions executable to cause a data processing apparatus to perform operations including: accessing a representation of a document category; accessing a set of documents, wherein each of the documents of the set is associated with a label indicating whether or not the document is associated with the document category; compiling a list of terms, wherein the list of terms includes distinct terms found in the documents of the set; computing information gain of each of the terms, wherein information gain is computed with regard to the document category; sorting the list by ordering the terms based on respective information gain; creating multiple association rules, wherein at least one of the association rules includes a logical conjunction of at least two terms of the list and one or more of the association rules includes at least one of the distinct terms; and performing an association rule analysis that includes performing the following operations with respect to each of the association rules: obtaining categorization results by using the association rule in categorizing each of the documents of the set with regard to the document category; recording the categorization results; and evaluating a precision of the association rule based on the respective categorization results.