What are Non-Functional Requirements in System Design? | Examples, Definition

The Non-functional requirements (NFRs) are the criteria that describe aspects of a system's operation that are not directly related to its specific behaviors or features. Unlike functional requirements, which specify what the system should do, non-functional requirements define how the system should perform, its quality attributes, constraints, and other characteristics that affect its overall operation and usability. Non-functional requirements are essential for ensuring that the system meets performance, security, usability, and other quality standards.

Types of Non-Functional Requirements

1. Performance Requirements:
   • Response Time: Specifies the maximum time the system should take to respond to user requests.
   • Throughput: Defines the number of transactions or operations the system should handle within a specific timeframe.
   • Scalability: Specifies the system's ability to handle increased load by adding resources without significant performance degradation.
   • Concurrency: Specifies the number of users or processes the system can support simultaneously.
2. Reliability and Availability Requirements:
   • Reliability: Specifies the system's ability to perform its functions consistently and predictably over time without failure.
   • Availability: Defines the percentage of time the system should be operational and accessible to users.
   • Fault Tolerance: Specifies the system's ability to continue operating in the event of hardware or software failures.
3. Security Requirements:
   • Authentication: Specifies how users are verified and authenticated when accessing the system.
   • Authorization: Defines the access rights and permissions granted to users based on their roles and privileges.
   • Auditing and Logging: Specifies the system's ability to track and record user activities, changes, and security events for auditing and compliance purposes.
4. Usability Requirements:
   • Ease of Use: Specifies the system's intuitiveness, simplicity, and user-friendliness.
   • Accessibility: Defines the system's ability to be used by people with disabilities and conform to accessibility standards.
   • User Interface Design: Specifies the visual layout, navigation, and interaction design of the system's user interface.
5. Compatibility Requirements:
   • Interoperability: Specifies the system's ability to communicate and exchange data with other systems or components.
   • Platform Compatibility: Defines the platforms, operating systems, browsers, or devices the system should be compatible with.

Non-Functional Requirements Example

Let us consider a simple example of Non-Functional Requirements for a web-based e-commerce system

• The system should load the homepage within 3 seconds to provide a responsive user experience.
• The system should be available 99.9% of the time, excluding scheduled maintenance windows.
• User passwords must be stored securely using industry-standard encryption algorithms to prevent unauthorized access to user accounts.
• The system codebase should be well-documented and follow coding standards to facilitate future maintenance and enhancements.
• The system should be compatible with the latest versions of popular web browsers such as Google Chrome, Mozilla Firefox, and Microsoft Edge.

These non-functional requirements outline various aspects of the system's performance, reliability, security, usability, maintainability, and compatibility that are essential for ensuring the overall effectiveness and suitability of the e-commerce platform.