A Lightweight Approach to Consistency of Scenarios and Class Models

Today, object-oriented requirements specifications typically combine a scenario (or use case) model and a class model for expressing functional requirements. With any such combination, the problem of consistency between these two models arises. In this paper, we present a lightweight approach to consistency between a scenario model and a class model. We assume semi-formal, loosely coupled models that are complementary: scenarios model the external system behavior; the class model specifies the internal, state-dependent functionality that cannot be expressed easily in a scenario (but is required to specify external behavior properly). We achieve consistency by minimizing overlap between the two models and by systematically cross-referencing corresponding information. We give a set of rules that can be used both for developing a consistent specification and for checking the consistency of a completed specification. Some rules can be checked automatically, the others are rules for manual inspection.