機能要件Functional requirements

Learn in the textbookRequirements Definition and Design

DefinitionFunctional requirements (機能要件) define what the system does: the processes and functions it provides for the business.

ExplanationRequirements definition analyzes business workflows and usage to list the processing the system will take on. In a library lending system, for example, "record a loan by member number" and "list books past their return date" are functional requirements. The finer naming scheme for phases includes system requirements definition (システム要件定義), which covers the whole system, and software requirements definition (ソフトウェア要件定義), which covers the software inside it.

AnalogyIt is like the list of dishes on a restaurant menu. It fixes what the restaurant can serve, but says nothing yet about how to cook them.

Learn in the textbookBusiness Requirements Definition — Functional / Non-functional Requirements and Agreement

DefinitionFunctional requirements (機能要件) define what the system does (the data it accepts, the processing it performs, and the screens and reports it outputs) to meet the business requirements.

ExplanationProcessing such as registering an order or totaling the amount to bill at month-end counts as a functional requirement. In other words, it takes the part of the business the system handles and writes it down as what the system does.

AnalogyFor a vending machine, these are the jobs the machine itself does: taking money, dispensing the product, and returning change.