Functional Requirement

Definition

Functional Requirement

any requirement that specifies a mandatory behavior

Classification

As illustrated in the preceding figure, Functional Requirement is part of the following inheritance hierarchy:

• Type: Abstract
• Superclass: Requirement
• Subclasses:
  • Textual requirement
  • Use Case Requirement
  • Use Case Path Requirement
  • Use Case Path Interaction Requirement
  • Use Case Path Postcondition Requirement
  • Change Case Requirement
  • Change Case Path Requirement
  • Misuse Case Requirement
  • Misuse Case Path Requirement

Responsibilities

The typical responsibilities of a functional requirement are to specify:

• A fundamental reason why something exists.
• An action that it must be able to take (i.e., a function that it must be able to perform).
• What it must do in order to complete some part of a business process.

Guidelines

The following guidelines have been found to be useful when producing functional requirements:

• Do not confuse functional requirements with constraints or other types of requirements.
• Functional requirements are often characterized by verbs, whereas quality requirements are often characterized by adjectives.
• A functional requirement is typically specified in the functional requirements section of the system requirements specification.