Disciplines > Requirements > Concepts > Types of Requirements

More Information: Concepts: Requirements
Concepts: Requirements Management
Concepts: Traceability
White Paper: Applying Requirements Management with Use Cases

Traditionally, requirements are looked upon as statements of text fitting into one of the categories mentioned in Concepts: Requirements. Each requirement states "a condition or capability to which the system must conform".

To perform effective requirements management, we have learned that it helps to extend what we maintain as requirements beyond only the detailed "software requirements". We introduce the notion of requirements types to help separate the different levels of abstraction and purposes of our requirements. 

We may want to keep track of ambiguous "wishes", as well as formal requests, from our stakeholders to make sure we know how they are taken care of. The Vision document helps us keep track of key "user needs" and "features" of the system. The use-case model is an effective way of expressing detailed functional "software requirements", therefore use cases may need to be tracked and maintained as requirements, as well as perhaps individual statements within the use case properties which state "conditions or capabilities to which the system must conform". Supplementary Specifications may contain other "software requirements", such as design constraints or legal or regulatory requirements on our system. For a complete definition of the software requirements, use cases and Supplementary Specifications may be packaged together to define a Software Requirements Specification (SRS) for a particular "feature" or other subsystem grouping.

The larger and more intricate the system developed, the more expressions, or types of requirements appear and the greater the volume of requirements. "Business rules" and "vision" statements for a project trace to "user needs", "features" or other "product requirements". Use cases or other forms of modeling and other Supplementary Specifications drive design requirements, which may be further decomposed to functional and non-functional "software requirements" represented in analysis & design models and diagrams.

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