What is the difference between functional and non-functional requirements?

Functional requirements and non-functional requirements serve distinct roles in system design, making the distinction critical for successful project outcomes. Functional requirements delineate specific behaviors and functionalities that a system must exhibit; they essentially outline what tasks the system should perform and dictate its capabilities in response to various inputs. For example, a functional requirement might state that a user must be able to log in or generate a report.

On the other hand, non-functional requirements refer to the criteria that dictate how the system operates rather than what it does. These requirements address the quality attributes, constraints, or standards to be adhered to, such as performance metrics, usability factors, reliability, scalability, and security considerations. For instance, a non-functional requirement might specify that the system must handle 1000 simultaneous users or that it should be accessible within a certain loading time.

Understanding this distinction is crucial for analysts and designers to create a system that not only meets the necessary functionality but also performs reliably and efficiently under specified conditions. This comprehensive approach to both types of requirements ensures that stakeholders' expectations are met and that the system is robust and user-friendly.