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FURPS (Functionality, usability, reliability, performance, supportability) is a model for classifying software quality attributes (functional and non-functional requirements):

• Functionality - capability (size and generality of feature set), reusability (compatibility, interoperability, portability), security (safety and exploitability)
• Usability (UX) - human factors, aesthetics, consistency, documentation, responsiveness
• Reliability - availability (failure frequency (robustness/durability/resilience), failure extent and time-length (recoverability/survivability)), predictability (stability), accuracy (frequency/severity of error)
• Performance - speed, efficiency, resource consumption (power, ram, cache, etc.), throughput, capacity, scalability
• Supportability (serviceability, maintainability, sustainability, repair speed) - testability, flexibility (modifiability, configurability, adaptability, extensibility, modularity), installability, localizability

The model, developed at Hewlett-Packard was first publicly elaborated by Grady and Caswell. FURPS+ is now widely used in the software industry. The + was later added to the model after various campaigns at HP to extend the acronym to emphasize various attributes, such as Design Requirements, Implementation Requirements, Interface Requirements and Physical Requirements.^[1]

• Types of requirements
• Expanded list of types of requirements

• Watson, Mike (2006). Managing Smaller Projects: A Practical Approach. Multi-Media Publications Inc. pp. 117 ff. ISBN 978-1-895186-85-7.
• Kenett, Ron; Baker, Emanuel (1999). Software Process Quality: Management and Control. CRC Press. pp. 130 ff. ISBN 978-0-8247-1733-9.
• Nakajo, Takeshi; Sasabuchi, Katsuhiko; Akiyama, Tadashi (April 1989). "A Structured Approach to Software Defect Analysis" (PDF). Hewlett-Packard Journal. 40 (2). Palo Alto: Hewlett-Packard Co.: 50–56. Archived from the original (PDF) on 2023-03-13. Retrieved 2016-03-24.
• Fischer, William A. Jr.; Jost, James W. (April 1989). "Comparing structured and unstructured methodologies in firmware development" (PDF). Hewlett-Packard Journal. 40 (2). Palo Alto: Hewlett-Packard Co.: 80–85. Archived from the original (PDF) on 2023-03-13. Retrieved 2016-03-24.
• Grady, Robert; Caswell, Deborah (1987). Software Metrics: Establishing a Company-wide Program. Prentice Hall. pp. 159. ISBN 0-13-821844-7.
• Carter, Donald; Stilwell Baker, Barbara (1992). Concurrent Engineering, The Product Development Environment for the 1990s. Addision-Wesley. pp. 175. ISBN 0-201-56349-5.

• IBM on Furps+