requirement

A requirement is a statement describing a condition or capability that must be met or possessed by a system, product, service, or process to satisfy a stakeholder need or constraint. Requirements express what the system should do (functional) or how the system should behave non-functionally (non-functional), and may address performance, reliability, security, usability, or regulatory compliance. Requirements can be categorized as stakeholder requirements (high-level goals of users or sponsors), system requirements (more concrete, for architects and developers), and design constraints (limits on technology, standards, or interfaces).

The discipline of requirements engineering covers identifying, documenting, validating, and managing these requirements throughout a project's life cycle. Key activities include elicitation (gathering needs from stakeholders), analysis and refinement (resolving conflicts and specifying must-haves), specification (writing clear, testable statements, often in a requirements specification document), verification and validation (checking that requirements are correct and that the project delivers them), and traceability (linking requirements to design elements and tests) to control scope changes.

Quality characteristics include clarity, consistency, completeness, verifiability, feasibility, and traceability. Common issues include ambiguity, conflicting requirements, incomplete coverage, and scope creep. Examples: functional: "The system shall allow users to reset passwords via email." Non-functional: "Response time shall be under 2 seconds under typical load." In practice, standards and methodologies guide how requirements are written and validated, and successful projects rely on well-managed, testable requirements aligned with stakeholder needs.