What Are Functional Requirements?
Functional requirements specify which functions your system (or system component) must have. In other words, they define what your custom software needs to do. If these requirements are not met, the software fails; it’s non-negotiable. Examples of the most common functional requirements are (1) use cases and (2) document descriptions.
Use cases can be numbered lists with text or diagrams that describe user actions. Each use case illustrates behavioral scenarios through one or more functional requirements. First, a set of use cases is selected — and then an analyst can derive the functional requirements that need to be implemented in order for each use case to be fulfilled. For example, a navigational use-case model for a conference management system is proposed in the diagram below. Each main functionality is associated with user roles: Here’s an example of a use case numbered list for a subway ticket machine: