Types Of Requirements

Requirements are categorized in several ways. The following are common categorizations of requirements that relate to technical management.

- Customer Requirements
Statements of fact and assumptions that define the expectations of the system in terms of mission objectives, environment, constraints, and measures of effectiveness and suitability (MOE/MOS). The customers are those that perform the eight primary functions of systems engineering, with special emphasis on the operator as the key customer.
* Operational distribution or deployment: Where will the system be used?
* Mission profile or scenario: How will the system accomplish its mission objective?
* Performance and related parameters: What are the critical system parameters to accomplish the mission?
* Utilization environments: How are the various system components to be used?
* Effectiveness requirements: How effective or efficient must the system be in performing its mission?
* Operational life cycle: How long will the system be in use by the user?
* Environment: What environments will the system be expected to operate in an effective manner?

- Functional Requirements
Functional requirements explain what has to be done by identifying the necessary task, action or activity that must be accomplished. Functional requirements analysis will be used as the toplevel functions for functional analysis.

- Non-functional Requirements
Non-functional requirements are requirements that specify criteria that can be used to judge the operation of a system, rather than specific behaviors.

- Performance Requirements
The extent to which a mission or function must be executed; generally measured in terms of quantity, quality, coverage, timeliness or readiness. During requirements analysis, performance (how well does it have to be done) requirements will be interactively developed across all identified functions based on system life cycle factors; and characterized in terms of the degree of certainty in their estimate, the degree of criticality to system success, and their relationship to other requirements.

- Design Requirements
The “build to,” “code to,” and “buy to” requirements for products and “how to execute” requirements for processes expressed in technical data packages and technical manuals.

- Derived Requirements
Requirements that are implied or transformed from higher-level requirement. For example, a requirement for long range or high speed may result in a design requirement for low weight.

- Allocated Requirements
A requirement that is established by dividing or otherwise allocating a high-level requirement into multiple lower-level requirements. Example: A 100-pound item that consists of two subsystems might result in weight requirements of 70 pounds and 30 pounds for the two lower-level items.