2. Manage Requirements

Requirements management is a systematic approach to eliciting, organizing, communicating, and managing the changing requirements of a software-intensive system or application.

The benefits of effective requirements management are numerous:

• Better control of complex projects. This includes greater understanding of the intended system behavior as well as prevention of requirements creep.
• Improved software quality and customer satisfaction. The fundamental measure of quality is whether a system does what it is supposed to do. With the Rational Unified Process, this can be more easily assessed because all stakeholders have a common understanding of what must be built and tested.
• Reduced project costs and delays. Fixing errors in requirements is very expensive. With effective requirements management, you can decrease these errors early in the development, thereby cutting project costs and preventing delays.
• Improved team communication. Requirements management facilitates the involvement of users early in the process, helping to ensure that the application meets their needs. Well-managed requirements build a common understanding of the project needs and commitments among the stakeholders: users, customers, management, designers, and testers. It is often difficult to look at a traditional object-oriented system model and tell how the system does what it is supposed to do. This difficulty stems from the lack of a consistent, visible thread through the system when it performs certain tasks. In the Rational Unified Process, use cases provide that thread by defining the behavior performed by a system.

Use cases are not required in object orientation, nor are they a compulsory vehicle in the Rational Unified Process. Where they are appropriate, however, they provide an important link between system requirements and other development artifacts, such as design and tests. Other object-oriented methods provide use-case-like representation but use different names for it, such as scenarios or threads.

The Rational Unified Process is a use-case-driven approach, which means that the use cases defined for the system can serve as the foundation for the rest of the development process. Use cases used for capturing requirements play a major role in several of the process workflows, especially design, test, user-interface design, and project management. They are also critical to business modeling.