A Formal Model of Use-Cases and Its Application in Generating A Hierarchical Class-Structure

Creating an object-oriented design from user requirements, given as a set of use-cases, means deriving a detailed class structure that can support an implementation of those requirements. We introduce here the Augmented Finite-State (AFS) model for a set of use-cases. An AFS model of a single usecase U incorporates the inputs, outputs, and operations for each interaction in U , including the ”internal” dataflows among those interactions. The AFS model for a set of use-cases U combines the AFS models of individual use-cases Uj ∈ U to account for common interactions among Uj ’s and the control-flows among Uj ’s. After we decompose the combined model into a unique set of disjoint Maximal Linear Segments (MLSs), we derive one class from each MLS and finally create the class-hierarchy based on the next-relationship among the MLSs. One advantage of our approach over those based on the concept-analysis is that the AFS model gives a simple controller for the call-sequences of the class-methods corresponding to each Uj . Keywords–Augmented finite-state model; class hierarchy; objectoriented design; refactoring; use-case model.