What are functional and non-functional requirements in system design?

In system design, functional and non-functional requirements play crucial roles in outlining what a system is supposed to do and how it should perform, respectively. Understanding these requirements is essential for developing a system that meets the needs of its users and operates effectively under various conditions.

Functional Requirements

Functional requirements describe the specific behaviors or functionalities that a system must have. They define the actions the system must take or the features it needs to support in response to particular inputs or conditions. These requirements are directly related to what the system is supposed to do.

Examples of Functional Requirements:

1. User Authentication: Users must be able to log in to their accounts using a username and password.
2. Data Processing: The system must be able to process payments and generate receipts for transactions instantly.
3. Search Functionality: Users should be able to search for products using keywords, and the system should display all relevant results sorted by relevance.
4. Report Generation: The system must generate monthly sales reports that can be exported in CSV and PDF formats.
5. Notification System: Users should receive real-time notifications via email and SMS for transaction confirmations.

These requirements are usually captured in detailed descriptions of the software services, interfaces, and interactions with the user or other systems.

Non-Functional Requirements

Non-functional requirements specify how the system performs certain functions, emphasizing the quality and criteria the system should meet. These are not about specific behaviors but about the system's attributes and how it handles operations. They are crucial for ensuring the system's reliability, efficiency, and user satisfaction.

Examples of Non-Functional Requirements:

1. Performance: The web application should load within two seconds, and search results should be displayed within three seconds.
2. Scalability: The system must support up to 10,000 simultaneous users without degradation of performance.
3. Reliability: The system should have an uptime of 99.9%, with automatic failover to a backup server in less than one minute in the event of a primary server failure.
4. Usability: The interface should be user-friendly, with the ability to complete most tasks in no more than three clicks. Compliance with the Web Content Accessibility Guidelines (WCAG) is required for accessibility.
5. Security: All user data must be encrypted using AES-256 encryption, and the system must comply with GDPR and other relevant privacy regulations.
6. Maintainability: The system should be easy to update, with the capability to deploy new updates with minimal downtime. Code should be well-documented to facilitate maintenance.

Importance of Distinguishing Between These Requirements

Understanding the distinction between functional and non-functional requirements is essential for developers, stakeholders, and testers:

• Developers need this distinction to build and test the system correctly.
• Stakeholders need to ensure that the system will meet their business objectives and operational needs.
• Testers use these requirements as benchmarks for validating and verifying system features and performance.

Conclusion

In system design, both functional and non-functional requirements are foundational elements that guide the development process. Functional requirements focus on what the system does, while non-functional requirements focus on how the system performs its functions, ensuring it meets broader quality standards. Properly defining both types of requirements is crucial for developing a robust, user-friendly, and effective system.