Investigating the Role of Use Cases in the Construction of Class Diagrams

Several approaches have been proposed for the transition from functional requirements to object-oriented design. In a use case-driven development process, the use cases are important input for the identification of classes and their methods. There is, however, no established, empirically validated technique for the transition from use cases to class diagrams. One recommended technique is to derive classes by analyzing the use cases. It has, nevertheless, been reported that this technique leads to problems, such as the developers missing requirements and mistaking requirements for design. An alternative technique is to identify classes from a textual requirements specification and subsequently apply the use case model to validate the resulting class diagram. This paper describes two controlled experiments conducted to investigate these two approaches to applying use case models in an object-oriented design process. The first experiment was conducted with 53 students as subjects. Half of the subjects used a professional modelling tool; the other half used pen and paper. The second experiment was conducted with 22 professional software developers as subjects, all of whom used one of several modelling tools. The first experiment showed that applying use cases to validate class diagrams constructed from textual requirements led to more complete class diagrams than did the derivation of classes from a use case model. In the second experiment, however, we found no such difference between the two techniques. In both experiments, deriving class diagrams from the use cases led to a better structure of the class diagrams. The results of the experiments therefore show that the technique chosen for the transition from use cases to class diagrams affects the quality of the class diagrams, but also that the effects of the techniques depend on the categories of developer applying it and on the tool with which the technique is applied.