An evaluation of applying use cases to construct design versus validate design

Use case models capture and describe the functional requirements of a software system. A use case driven development process, where a use case model is the principal basis for constructing an object-oriented design, is recommended when applying UML. There are, however, some problems with use case driven development processes and alternative ways of applying a use case model have been proposed. One alternative is to apply the use case model in a responsibility-driven process as a means to validate the design model. We wish to study how a use case model best can be applied in an object-oriented development process and have conducted a pilot experiment with 26 students as subjects to compare a use case driven process against a responsibility-driven process in which a use case model is applied to validate the design model. Each subject was given detailed guidelines on one of the two processes, and used those to construct design models consisting of class and sequence diagrams. The resulting class diagrams were evaluated with regards to realism, that is, how well they satisfied the requirements, size and number of errors. The results show that the validation process produced more realistic class diagrams, but with a larger variation in the number of classes. This indicates that the use case driven process gave more, but not always more appropriate, guidance on how to construct a class diagram. The experiences from this pilot experiment were also used to improve the experimental design, and the design of a follow-up experiment is presented.