非機能要件Non-functional requirements

Learn in the textbookRequirements Definition and Design

DefinitionNon-functional requirements (非機能要件) set the level and conditions at which functions are provided, such as response speed, resistance to outages, security, and ease of operation.

ExplanationLike functional requirements, non-functional requirements get their targets during requirements definition. Stating targets in a checkable form, such as numbers, makes it easier to judge later whether they were met.

AnalogyIt is like a restaurant promising to serve food within 10 minutes of the order. It sets the standard of service, not the kinds of dishes.

Memory hookThe "non-" does not deny the functions; it points to conditions other than the functions themselves. Read it as conditions attached once the functions are in place.

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

DefinitionNon-functional requirements (非機能要件) define the conditions a system must meet beyond its functions themselves (quality levels such as performance, reliability, and security, plus technical and operational conditions).

ExplanationHow many seconds a screen takes to respond, how long the system may be down in a year, and how data is protected all fall here. Even for the same function, the required level changes the equipment and cost needed.

AnalogyFor the same vending machine, these are the conditions beyond the jobs it does: how many seconds after a button press the product comes out, how many years it runs without breaking down, and how often it is inspected.