Non-functional requirements, also known as quality attributes or system properties, specify the characteristics and constraints that define the overall behavior, performance, and user experience of a software system. Unlike functional requirements that describe specific features and functionalities, non-functional requirements focus on the system's attributes, qualities, and constraints. Here are some common categories of non-functional requirements:
1. Performance: Specifies how the system should behave in terms of response time, throughput, scalability, and resource utilization. Examples include:
- Response time should be less than 200 milliseconds for a given operation.
- The system should handle a minimum of 1000 concurrent users.
- The system should process a minimum of 1000 requests per second.
2. Security: Describes the measures and constraints related to the protection of the system, data, and users' privacy. Examples include:
- User authentication and authorization mechanisms should be implemented.
- Access to sensitive data should be restricted to authorized users.
- The system should be protected against common security threats, such as cross-site scripting (XSS) or SQL injection.
3. Reliability: Defines the system's ability to perform its functions consistently and without failure over a specified period. Examples include:
- The system should have an uptime of 99.9%.
- The system should be able to recover from failures within 5 minutes.
- The system should handle 100,000 transactions without data loss.
4. Availability: Specifies the system's accessibility and uptime requirements, including maintenance windows and backup strategies. Examples include:
- The system should be available 24/7, except for scheduled maintenance windows.
- The system should provide a failover mechanism for high availability.
- Backup and restore procedures should be performed daily.
5. Usability: Refers to the ease of use and user experience of the system. It includes factors like user interface design, accessibility, and user assistance. Examples include:
- The system should have an intuitive and user-friendly interface.
- The system should be accessible to users with disabilities.
- Help documentation and tutorials should be provided to assist users.
6. Scalability: Describes the system's ability to handle increased workload and adapt to changing demands by adding resources. Examples include:
- The system should be able to scale horizontally to accommodate additional users.
- The system should be able to handle a ten-fold increase in data volume without performance degradation.
- The system should support load balancing to distribute requests across multiple servers.
7. Maintainability: Specifies the ease with which the system can be modified, updated, repaired, or extended. Examples include:
- The system's code should follow coding standards and best practices.
- Changes to the system should be easily deployable without impacting existing functionality.
- The system should have comprehensive documentation to aid in maintenance and troubleshooting.
8. Compliance: Refers to adherence to legal, regulatory, and industry-specific requirements and standards. Examples include:
- The system should comply with relevant data protection regulations, such as GDPR or HIPAA.
- The system should meet industry-specific security standards, such as PCI DSS for payment processing.
- The system should follow accessibility guidelines, such as WCAG 2.0 for web accessibility.
These are just a few examples of non-functional requirements. The specific non-functional requirements for a software system depend on its nature, context, and stakeholder needs. It's important to identify and define non-functional requirements early in the software development process to ensure that the system meets the desired quality attributes.