1 Introduction

When modelling OO software with UML (Object Management Group, 1999) the 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 use case diagrams, statechart diagrams, activity diagrams, sequence diagrams and collaboration diagrams.

In software engineering, it is widely recognised that the structural properties of conceptual models, i.e. those models obtained at early phases of the development have a great influence on the quality of the software product that is finally implemented. For this reason, as Chapter 4 reveals, several proposals of metrics exists for structural diagrams, such as proposals of metrics that can be applied to measure the size, structural complexity, coupling, etc. of UML class diagrams. The behavioural diagrams have been slightly disregarded in the software measurement field. Since the late 90's, some proposals of metrics for use cases diagrams have appeared (see Chapter 3). However, there is little reference to metrics for behavioural diagrams such as UML statechart diagrams, sequence diagrams, activity diagrams and collaboration diagrams in the existing literature (see Sec. 2).

Despite this situation, several authors such as Poels and Dedene (2000b) and Brito e Abreu et al. (2000; 2002) among others, pointed out that the definition of metrics for diagrams that capture dynamics aspects of OO software is an interesting topic for investigation. This fact...