Functional requirement

A functional requirement defines a function of a system or one of its components, where a function is a summary of the behavior linking a system inputs to its outputs, covering calculations, data manipulation, technical details and the specific behavior a system must exhibit. Functional requirements are typically phrased as the system must do something, while non-functional or quality requirements, phrased as the system shall be something, describe overall characteristics such as performance, security and reliability instead of specific actions. Functional requirements are detailed in a system design and drive its application architecture, while non-functional requirements are detailed in system architecture and drive its technical architecture. Functional requirements often originate from organizational or business rules discovered through discussions with users and stakeholders, and form the basis for use cases, from which analysts derive specific requirements based on observed user needs. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/