Quality of service requirements are a subset of which types of requirements?

Quality of service requirements belong to non-functional requirements because they specify the criteria that can be used to judge the operation of a system rather than the specific behaviors or functionalities it provides. Non-functional requirements encompass a wide range of aspects, including performance, usability, reliability, and security, which are vital to the overall user experience and system performance but do not concern what the system does specifically.

Quality of service focuses on how well a system performs its functions, covering aspects such as response time, availability, and scalability. These characteristics are essential for ensuring that the system meets user expectations and operational standards, making them a critical part of non-functional requirements. By understanding that quality of service is a subset of non-functional requirements, one recognizes the importance of these criteria in the overall system design and evaluation process.