Non Functional Requirements
System quality attributes and constraints beyond specific behaviors
Non Functional Requirements specify how a system performs rather than what it does, defining quality attributes, constraints, and system properties. While functional requirements describe specific behaviors and features, non-functional requirements address performance, security, usability, reliability, and other quality characteristics. Common categories include performance requirements like response time and throughput, scalability requirements for handling growth, security requirements protecting data and access, usability requirements for ease of use, reliability and availability targets, maintainability for future changes, compatibility with other systems, regulatory and compliance needs, and operational requirements. For example, pages must load within two seconds, system must handle ten thousand concurrent users, data must be encrypted at rest and in transit, or application must be accessible meeting WCAG standards. Non-functional requirements significantly impact user satisfaction, often more than specific features. Slow performance frustrates users regardless of functionality. Poor security creates risk and erodes trust. Non-functional requirements also affect technical architecture, technology choices, development effort, and ongoing costs. They're often harder to test than functional requirements, requiring specialized testing approaches like load testing, security audits, and usability studies. Best practices include defining non-functional requirements early as they shape architecture, making them specific and measurable, prioritizing them by importance, allocating appropriate resources, testing them systematically, and monitoring them in production. Common mistakes include treating non-functional requirements as afterthoughts, making them vague and untestable, assuming they'll be handled without explicit requirements, or neglecting some categories entirely. Product managers must ensure non-functional requirements receive appropriate attention, balancing functional development with quality attributes, advocating for investments in performance, security, and usability, and making tradeoffs explicit when conflicts arise. Strong non-functional requirements create products that not only work but work well.
Understand Non Functional Requirements in product development. Learn how quality attributes like performance and security shape product success.