Non-Functional Requirements (NFRs)
What Are Non-Functional Requirements?
Non-functional requirements (NFRs) define the quality attributes, system constraints, and operational characteristics of a system.
Unlike functional requirements, which specify what a system should do, non-functional requirements describe how well the system performs, behaves, or operates.
Key Categories of NFRs
- Performance – Speed, responsiveness, and throughput
e.g., "The system must process 1,000 transactions per second" - Scalability – Ability to handle increased load
e.g., "The system must support 10,000 concurrent users" - Reliability & Availability – System uptime and failure recovery
e.g., "99.99% uptime required" - Security – Protection from unauthorized access
e.g., "All user data must be encrypted" - Usability – User experience and ease of use
e.g., "Users should complete registration in less than 2 minutes" - Maintainability – Ease of system updates and bug fixes
e.g., "Code should have at least 80% test coverage" - Portability – Ability to run on different environments
e.g., "The application must be compatible with Windows, Linux, and macOS" - Compliance – Adherence to legal and regulatory requirements
e.g., "System must comply with GDPR"
Why Are NFRs Important?
- Ensure system stability, security, and performance.
- Affect user satisfaction and business success.
- Impact architecture and technology choices.
- Must be defined early to avoid costly rework.