Identify Functional Requirements (Process Notes 3.2)

When the use case is large and/or complex and/or unfamiliar, it is difficult to make the leap directly from the use case to the requirements. A scenario provides a steppingstone to the functional requirements in this situation.

From the point of view of the actor(s), write the scenario by listing the steps that the product must go through to do the work of the use case. For each scenario step, find the functional requirements by breaking the step into testable one-sentence statements. Ask what the product has to do to complete the work of this step. The following questions are helpful in this regard:

• What data must be received by the product?

• What data must be produced by the product?

• What data must be recorded by the product?

• What checks must be made by the product?

• What decisions must be made by the product?

• What calculations must be made by the product?

Each of the above questions might produce a number of functional requirements. For each requirement:

• Write a description using the form "The product shall . . ." followed by the action that the product must take.

• Give the requirement a unique number.

• Attach the use case number to the requirement.

• Record the source (preferably names of people) of the requirement.

• Record the requirement rationale. Why is this requirement important to the business?

Chapter 7 focuses on functional requirements.