I. Introduction
Among many alternative means for knowledge representation, rules seem to be one of the most common forms for expressing various types of knowledge for a number of reasons [1]. It has been argued that other knowledge representation schemes can be transformed into logic (rule)-based schemes [2]–[4]. As such, knowledge-based systems (e.g., rule-based expert systems), usually constructed from human knowledge in forms of if–then rules, have become the most visible and fastest growing branch of artificial intelligence (AI) [1].