Earlier in the book we introduced the concepts of the use case and the actors that participate in them. We used them in Chapter 6 to model a business system and in Chapter 7 to help define the system boundaries for our case study. In this chapter, we take a more thorough look at the use-case method, to help you understand the motivation for using use cases and to learn how to apply them in a more rigorous manner.
However, it is not the purpose of the book to teach you everything there is to know about use cases. The purpose of this chapter is to provide a basic grounding in use cases so you can understand how to apply them throughout the requirements- intensive portion of the product development cycle. We'll apply use cases as the primary container for the software requirements we are so intent on managing. We'll use them again in Chapter 25 (to assure that the system design implements the use cases and the requirements we've agreed to) and in Chapter 26 (to provide a pattern to drive our test case development and testing activities).