Defining and Validating Metrics for UML Statechart Diagrams

Maintainability is an increasingly relevant quality aspect in the development of object oriented software systems (OOSS). It is generally accepted that OOSS maintainability is highly dependent on the decisions made early in the development life cycle. Conceptual modelling is an important task of this early development. So that the maintainability of conceptual models have a great influence on the maintainability of the OOSS which is finally implemented. For assessing the conceptual models maintainability it is useful to have quantitative and objective measurement instruments. Conceptual modelling focus on either static aspects or dynamics aspects of the OOSS. Using the Unified Modelling Language (UML) static aspects at conceptual level are mainly represented in structural diagrams such as class diagrams, whilst dynamic aspects are represented in behavioural diagrams such as statechart diagrams, activity diagrams, sequence diagrams and collaboration diagrams. There exists several works related to metrics for structural diagrams such as class diagrams. However, behavioural diagrams have been little studied This fact leaded us to define measures for UML statechart diagrams. The main goal of this paper is to show how we defined those measures in a methodological way, in order to guarantee their validity. We used the DISTANCE framework, based on measurement theory, to define and theoretically validate the measures. In order to gather empirical evidence that the proposed measures could be early maintainability indicators of UML statechart diagrams, we carried out a controlled experiment. The aim of the experiment was to investigate the relationship between the complexity of UML statechart diagrams and their understandability (one maintainability subcharacteristic).