Functional vs Non-Functional Requirements

Few days ago I talked briefly about what Functional and Non-Functional Requirements are.

Today I want to give more details about them, what types we might have and examples.

Functional Requirements:

Are product features or functions that developers must implement to enable users to accomplish their tasks. They describe system behavior under specific conditions.

1) User Authentication and Authorization:

Functions related to user identification and access control.

Example: "The system shall require users to authenticate with a username and password before accessing any user-specific features. Users must have different access levels based on their roles (e.g., admin, regular user)."

2) Data Management:

Functions related to the creation, retrieval, update, and deletion of data.

Example: "The system shall allow users to create, edit, and delete their own profiles. Changes to user profiles must be saved and reflected immediately across the system."

3) Search and Filtering:

Functions that enable users to search and filter information within the system.

Example: "The system shall provide a search functionality that allows users to search for products by name, category, or price range. Search results should be displayed within 3 seconds."

4) Reporting and Analytics:

Functions for generating and displaying reports and analytical data.

Example: "The system shall generate monthly sales reports and allow users to export the reports in PDF or Excel formats. The report should include total sales, number of transactions, and average order value."

5) Notification and Alerts:

Functions related to sending notifications or alerts to users.

Example: "The system shall send an email notification to users when their account balance falls below a specified threshold. Notifications should be sent immediately upon detecting the low balance."

6) Communication:

Functions that support communication between users or between the system and users.

Example: "The system shall provide a messaging feature that allows users to send and receive messages within the application. Messages should be delivered in real-time and stored for future reference."

7) Transaction Processing:

Functions related to processing financial transactions or other types of transactions.

Example: "The system shall process payment transactions through an integrated payment gateway. Each transaction must be validated and confirmed before being recorded in the system."

8) Data Validation and Error Handling:

Functions that ensure data entered by users is valid and handle any errors.

Example: "The system shall validate user input on forms to ensure all required fields are filled out correctly. If validation fails, an appropriate error message should be displayed."

9) Integration with External Systems:

Functions for interacting with other systems or services.

Example: "The system shall integrate with a third-party CRM system to synchronize customer information. Any updates to customer data in the system should be reflected in the CRM in real-time."

10) User Preferences and Settings:

Functions that allow users to customize their experience or configure system settings.

Example: "The system shall allow users to set their preferred language and theme. These settings should be saved and applied each time the user logs in."

Non-Functional Requirements:

Are a set of specifications that describe the system's operation capabilities and constraints. These are basically the requirements that outline how well it operates, including things like speed, security, reliability, data integrity, etc.

1) Performance Requirements:

Define the system’s performance characteristics, such as speed and responsiveness.

Example: "The system shall handle up to 1,000 concurrent users with no degradation in response time, and individual page load times must not exceed 3 seconds under peak load conditions."

2) Scalability Requirements:

Specify how well the system can scale in terms of user load, data volume, or other resources.

Example: "The system shall be able to scale horizontally by adding additional servers to handle increased traffic without requiring significant reconfiguration."

3) Availability and Reliability Requirements:

Define the system’s uptime and reliability expectations.

Example: "The system shall maintain 99.9% uptime, excluding scheduled maintenance periods. It must be designed to recover from failures within 5 minutes."

4) Security Requirements:

Outline measures for protecting the system from unauthorized access and ensuring data integrity and confidentiality.

Example: "The system shall use AES-256 encryption for all sensitive data stored in the database and TLS 1.2 for data transmitted over the network."

5) Usability Requirements:

Define how user-friendly and intuitive the system should be.

Example: "The system shall provide an intuitive user interface that follows established design patterns, and user satisfaction surveys should indicate an average score of at least 4 out of 5."

6) Maintainability Requirements:

Specify how easily the system can be maintained, updated, or repaired.

Example: "The system’s codebase shall be modular and well-documented, with at least 80% code coverage by automated tests to facilitate easier updates and maintenance."

7) Compatibility Requirements:

Define how well the system should work with other systems, platforms, or environments.

Example: "The system shall be compatible with major web browsers (Chrome, Firefox, Safari, Edge) and support mobile devices running iOS and Android."

8) Compliance Requirements:

Specify adherence to laws, regulations, and standards.

Example: "The system shall comply with GDPR regulations by ensuring users can access, correct, and delete their personal data, and must provide data export capabilities upon request."

9) Backup and Recovery Requirements:

Define the processes and frequency for backing up data and recovering from data loss or corruption.

Example: "The system shall perform daily backups of all data and provide a recovery mechanism that restores data to within the last 24 hours in case of a system failure."

10) Localization and Internationalization Requirements:

Specify support for multiple languages and regional settings.

Example: "The system shall support localization for at least five languages, including English, Spanish, French, German, and Chinese, and allow users to select their preferred language."

11) Environmental Requirements:

Define the conditions under which the system must operate, including physical and technical environments.

Example: "The system shall be capable of operating in environments with temperatures ranging from 10°C to 35°C and with humidity levels of 20% to 80%."

12) Documentation Requirements:

Specify the documentation that should accompany the system for users, administrators, and developers.

Example: "The system shall include user manuals, API documentation, and system operation guides, all of which must be updated with each new release and available online."

In summary, functional and non-functional requirements are crucial for defining the complete scope and quality of a system.

While Functional Requirements ensure that the system fulfills its intended purpose and meets user needs effectively, Non-Functional Requirements ensure that the system is robust, efficient, and compliant with relevant standards and regulations.

Together, functional and non-functional requirements provide a comprehensive framework for system development, guiding the design, implementation, and evaluation processes. They help ensure that the system not only meets its functional goals but also delivers a high-quality experience for users, adapts to changing conditions, and adheres to necessary standards and best practices.

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