Coupling and cohesion metrics for knowledge-based systems using frames and rules

Software systems and in particular also knowledge-based systems (KBS) become increasingly large and complex. In response to this challenge, software engineering has a long tradition of advocating modularity. This has also heavily influenced object-oriented development. For measuring certain important aspects of modularity, coupling and cohesion metrics have been developed. Metrics have also attracted considerable attention for object-oriented development. For KBS development, however, no such metrics are available yet. This article presents the core of the first metrics suite for KBS development, its coupling and cohesion metrics. These metrics measure modularity in terms of the relations induced between slots of frames through their common references in rules. We show the soundness of these metrics according to theory and report on their usefulness in practice. As a consequence, we propose using our metrics in order to improve KBS development, and developing other important metrics and assessing their theoretical soundness along these lines.