Evaluating the effect of composite states on the understandability of UML statechart diagrams

Abstract

UML statechart diagrams have become an important technique for describing the dynamic behavior of a software system. They are also a significant element of OO design, especially in code generation frameworks such as Model Driven Architecture (MDA). In previous works we have defined a set of metrics for evaluating structural properties of UML statechart diagrams and have validated them as early understandability indicators, through a family of controlled experiments. Those experiments have also revealed that the number of composite states had, apparently, no influence on the understandability of the diagrams. This fact seemed a bit suspicious to us and we decided to go a step further. So in this work we present a controlled experiment and a replication, focusing on the effect of composite states on the understandability of UML statechart diagrams. The results of the experiment confirm, to some extent, our intuition that the use of composite states improves the understandability of the diagrams, so long as the subjects of the experiment have had some previous experience in using them. There are educational implications here, as our results justify giving extra emphasis to the use of composite states in UML statechart diagrams in Software Engineering courses. © Springer-Verlag Berlin Heidelberg 2005.