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.