Chapter 20. Software Requirements-A More Rigorous Look | Managing Software Requirements[c] A Use Case Approach

Chapter 20. Software Requirements ”A More Rigorous Look

Key Points

A complete set of requirements can be determined by defining the inputs, outputs, functions, and attributes of the system plus the attributes of the system environment.
Requirements should exclude project- related information, such as schedules, project plans, budgets , and tests, as well as design information.
The requirements/design process is iterative; requirements lead to the selection of certain design options, which in turn may initiate new requirements.
Design constraints are restrictions on the design of the system or on the process by which a system is developed.

In the prior team skills, the features we defined and the use-case model we developed for the system were purposely left at a high level of abstraction for the following reasons.

We can better understand the main characteristics of the system by focusing on its features and key use cases and how they fulfill user needs.
We can assess the system for its completeness, its consistency, and its fit within its environment.
We can use this information to determine feasibility and to manage the scope of the system before making significant resource investments.

In addition, staying at a high level of abstraction kept us from making overly constraining requirements decisions too early, that is, before the people closest to the system implementation have their opportunity to add their perspective and value to the system definition. In Team Skill 5, Refining the System Definition, our discussions transition to elaborating the system features in detail sufficient to ensure that the design and coding activities result in a system that fully conforms to the user needs. In so doing, we drive to the next level of specificity and detail, and we create a richer, deeper requirements model for the system to be built. Of course, we also create more information to be managed, and we will have to be better organized to handle this additional detail.