Guidelines: Important Decisions in Requirements

The following decisions should be made regarding the Requirements discipline's workflow:

Document the decisions in the Development Case, under the headings Disciplines, Requirements, Discipline.

Decide which artifacts to use and how to use each of them. The table below describes those artifacts you must have and those used in some cases. For more detailed information on how to tailor each artifact, and a discussion of the advantages and disadvantages of that specific artifact, read the section titled "Tailoring" for each artifact.

For each artifact, decide how the artifact should be used: Must have, Should have, Could have or Won't have. For more details, see Guidelines: Classifying Artifacts.

Artifact	Purpose	Tailoring (Optional, Recommended)
Use-Case Model (Actor,Use Case,Use-Case Package	Use cases are used to define functional requirements.	Recommended for most projects. Use cases are the recommended method for capturing functional requirements.
Use-Case Storyboard, Boundary Class	Projects with a large and complex user-interface should consider user-interface modeling and design.	Optional More informal prototyping and modeling may be sufficient on smaller development efforts.
Glossary	Ensures that everyone on the project is using a common vocabulary.	Recommended for most projects.
Requirements Attributes	A database of requirements attributes helps ensure that requirements are properly prioritized, tracked, and traced.	Optional However, on projects with relatively few requirements, a database of requirements attributes may not be strictly necessary.
Requirements Management Plan	Describes the information to be collected and control mechanisms to be used for measuring, reporting, and controlling changes to the product requirements. A separate document is needed if requirements management complexity or customer visibility warrants it.	Optional Projects with relatively few requirements may take a light-weight approach to requirements management which can be documented directly in the Software Development Plan. Other projects may select and follow a more rigorous approach, but produce little or no formal description. For example, the set of requirements attributes to be gathered may be implicitly documented by the configuration of the tools.
Software Requirements Specification	Used to collect the set of all requirements in a formal document provided to the customer.	Optional On less formal projects, a formal document may not be required.
Stakeholder Requests	Captures all requests made on the project, as well as how these requests have been addressed.	Recommended for most projects. In order to build a system that meets the needs of the stakeholders, it is important to solicit and review their requests. Many projects manage Stakeholder Requests as just a category of Change Requests. Other projects may capture Stakeholder Requests only informally.
Supplementary Specifications	Used to capture non-functional requirements.	Recommended for most projects.
User-Interface Prototype	Used to expose and test functionality and usability before the real development starts. It is an effective means of identifying missing requirements and requirements defects before too much time is wasted.	Recommended for most projects.
Vision	Captures very high-level requirements and design constraints, to give the reader an understanding of the system to be developed.	Recommended for most projects.

Tailor each artifact by performing the steps described in the Activity: Develop Development Case, under the heading "Tailor Artifacts per Discipline".

Decide Which Reports to Use

Decide How to Maintain Input Requirements

This section only applies if a formal contract, standard or specification document is imposing requirements to the requirements management effort. It is referred to as the "input requirements specification".

Decide whether the input requirements specification will be maintained or not. Will you go back and update the input requirements specification when you discover a requirement was bad, wrong or faulty? You must also decide how traces or references between the input requirement specification and the use cases will be maintained.

Most projects find that the number of requirements which are bad, faulty or wrong is so large, it doesn't make sense to maintain the original input requirements specification. Very few projects have customers willing to pay for the work of updating the input requirements specification with the new information revealed during use-case modeling.

Don't stress this topic too early. In the beginning of a project, people still believe in the initial requirements specification, however, after working through the problem area with a use case, most people have quite a different view of the initial requirements specification.

Decide How to Approve Use Cases

Decide how to approve the use cases. A lot of time can be saved by limiting the number of use cases that have to be formally reviewed by the customer. Perhaps it's acceptable for the customer to formally review only a subset of all use cases.

Secondary use cases are those use cases essential to the system but not to the task of the primary user; for example, use cases related to the administration and maintenance of the system, such as adding users to the system, changing their authority, and making backups. The system will not work without these use cases, although they're not of primary interest to the important users.

The strategy you use depends on your relationship with your customer. Do they trust that you can do the supporting use cases correctly without a formal approval process? Although this would save a considerable amount of time, will you reach the right quality of the use-case model?

Note: A solution to the problem may involve the customer in the Requirements effort. By involving customer representatives, they will be able to approve or give recommendations to other customers, and by involving the customer, the project gains credibility.