Use Cases and Feedback in Functional Requirements Analysis

Feedback exists in almost every stage of a software process and can improve the quality of the product generated from each stage. Use cases model is one important product of functional requirements analysis, so it should be updated continuously through feedback. This paper proposes a formal, three-level use cases model which consists of function use case level, system use case level and business use case level. A function use case is formalized with Hoare Logic, a system use case is composed of a set of function use cases according to three composition rules, and a business use case is formalized with a Petri Net. After the use cases model is proposed, how feedback in functional requirements analysis has effect on the model is well discussed. And changes of a function use case and a system use case are formally defined.