Types of Requirements

A requirement is:

1. A condition or capability needed by a stakeholder to solve a problem or achieve an objective.
2. A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed documents.
3. A documented representation of a condition or capability as in (1) or (2).

 Business Requirements - Are higher-level statements of the goals, objectives, or needs of the enterprise. They describe such things the reasons why a project is initiated, the things that the project will achieve, and the metrics which will be used to measure its success.

User Requirements - Are statements of the needs of a particular stakeholder or class of stakeholders. They describe the needs that a given stakeholder has and how that stakeholder will interact with a solution. User Requirements serve as a bridge between Business Requirements and the various classes of solution requirements.

Functional Requirements - Describe the behavior and information that the solution will manage. They describe capabilities the system will be able to perform in terms of behaviors or operations – a specific system action or response.

Quality of Service Requirements  - Capture conditions that do not directly relate to the  behavior or functionality of the solution, but rather describe environmental conditions under which the solution must remain effective or qualities that the systems must have. They are also known as non-functional or supplementary requirements.

Assumptions and constraints - Identify aspects of the problem domain that are not functional requirements of a solution, and will limit or impact the design of the solution.

Implementation requirements - Describe capabilities that the solution must have in order to facilitate transition from the current state of the enterprise to the desired future state, but that will not be needed once that transition is complete.