Use Cases
Chapter 6
USE-CASE MODEL: WRITING REQUIREMENTS IN CONTEXT
The indispensable first step to getting the things you want out of life: decide what you want. —Ben Stein
Objectives
• • • • Identify and write use cases. Relate use cases to user goals and elementary business processes. Use the brief, casual, and fully dressed formats, in an essential style. Relate use case work to iterative development.
Introduction
This chapter is worth studying during a first read of the book because use cases are a widely used mechanism to discover and record requirements (especially functional); they influence many aspects of a project, including OOA/D. It is worth both knowing about and creating use cases. Writing use cases—stories of using a system—is an excellent technique to understand and describe requirements. This chapter explores key use case concepts and presents sample use cases for the NextGen application. The UP defines the Use-Case Model within the Requirements discipline. Essentially, this is the set of all use cases; it is a model of the system's functionality and environment.
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6 - USE-CASE MODEL: WRITING REQUIREMENTS IN CONTEXT
6.1
Goals and Stories
Customers and end users have goals (also known as needs in the UP) and want computer systems to help meet them, ranging from recording sales to estimating the flow of oil from future wells. There are several ways to capture these goals and system requirements; the better ones are simple and familiar because this makes it easier—especially for customers and end users—to contribute to their definition or evaluation. That lowers the risk of missing the mark. Use cases are a mechanism to help keep it simple and understandable for all stakeholders. Informally, they are stories of using a system to meet goals. Here is an example brief format use case: Process Sale: A customer arrives at a checkout with items to purchase. The cashier uses the POS system to record each purchased item. The system presents
USE-CASE MODEL: WRITING REQUIREMENTS IN CONTEXT
The indispensable first step to getting the things you want out of life: decide what you want. —Ben Stein
Objectives
• • • • Identify and write use cases. Relate use cases to user goals and elementary business processes. Use the brief, casual, and fully dressed formats, in an essential style. Relate use case work to iterative development.
Introduction
This chapter is worth studying during a first read of the book because use cases are a widely used mechanism to discover and record requirements (especially functional); they influence many aspects of a project, including OOA/D. It is worth both knowing about and creating use cases. Writing use cases—stories of using a system—is an excellent technique to understand and describe requirements. This chapter explores key use case concepts and presents sample use cases for the NextGen application. The UP defines the Use-Case Model within the Requirements discipline. Essentially, this is the set of all use cases; it is a model of the system's functionality and environment.
45
6 - USE-CASE MODEL: WRITING REQUIREMENTS IN CONTEXT
6.1
Goals and Stories
Customers and end users have goals (also known as needs in the UP) and want computer systems to help meet them, ranging from recording sales to estimating the flow of oil from future wells. There are several ways to capture these goals and system requirements; the better ones are simple and familiar because this makes it easier—especially for customers and end users—to contribute to their definition or evaluation. That lowers the risk of missing the mark. Use cases are a mechanism to help keep it simple and understandable for all stakeholders. Informally, they are stories of using a system to meet goals. Here is an example brief format use case: Process Sale: A customer arrives at a checkout with items to purchase. The cashier uses the POS system to record each purchased item. The system presents