An empirical study of requirements model understanding: Use Case vs. Tropos models

Visual modelling languages are commonly used to support software requirements analysis and documentation. A variety of languages are available, based on different conceptual paradigms. They can be roughly divided into two main groups: goal-oriented approaches and scenario-based approaches. In the last ten years, numerous works developed case studies that illustrate the effectiveness and limitations of goal-oriented and scenario-based approaches. A few works even suggest coupling these approaches in order to capture requirements from different perspectives. However, experimental comparisons of these approaches have been rarely addressed. This paper presents the design and preliminary results of an empirical study that compares two state of the art requirements modelling methods: Use Cases, which is a scenario-based approach, and Tropos, which is a goal-oriented approach. The objective is to evaluate different levels of comprehension of requirements models expressed in both methods, as well as to estimate the time required to perform simple analysis tasks using both methods. Preliminary results show that Tropos models seem to be more comprehensible, although more time consuming, than Use Case models to novice requirements analysts.