Semantics based Cohesion and Coupling Metrics for Evaluating Understandability of State Diagrams

State diagrams commonly used for describing dynamic behavior of systems or objects can have various forms that specify the same behavior. Highly understandable state diagrams are important for efficient and clear communication between developers. Measurement of understandability of state diagrams is the first step to obtain highly understandable ones. Unfortunately, there is little research on metrics for evaluating state diagram's understandability. In this paper, we propose cohesion and coupling metrics, named Average Cohesiveness Of States (ACOS) and Average number of Similar States Of States (ASSOS), to evaluate understandability of state diagrams. To validate effectiveness of the metrics, we compared understandability of three state diagrams of different representations but the same behavior for two systems. The experiments showed that ACOS and ASSOS can capture understandability more correctly than existing structure-based metrics.