What are examples of functional and non-functional requirements?

Functional and non-functional requirements play critical roles in defining what a software system should do and how it should perform under various conditions. Here’s a breakdown to illustrate the difference between the two, along with examples:

Functional Requirements

Functional requirements describe specific behaviors or functions of a system. They detail what the system should do, the actions it must be able to perform, and the services it must provide to meet the needs of its users. These requirements are typically specific, measurable, and directly tied to business rules.

Examples:

1. User Authentication

   • Users must be able to log in using a username and password.
   • The system should support password recovery via email verification.

2. Data Management

   • Users should be able to create, read, update, and delete information in their profiles.
   • The system must automatically save draft emails every 2 minutes.

3. Search Functionality

   • The system must provide a search function that can filter results by date, relevance, and other criteria.
   • Search results should load within 3 seconds of submitting the query.

4. Order Processing

   • Customers must be able to add items to a shopping cart and proceed to checkout.
   • The system must calculate state tax and shipping costs based on the user’s location.

5. Reporting

   • The system must generate monthly sales reports that can be exported in CSV and PDF formats.
   • Users should receive real-time notifications on their dashboard for any critical metrics.

Non-Functional Requirements

Non-functional requirements specify criteria that can be used to judge the operation of a system, rather than specific behaviors. They are not about business rules or functional capabilities but about the user expectations in terms of system performance, usability, reliability, etc.

Examples:

1. Performance

   • The website should load within 3 seconds even under the load of up to 10,000 users at any one time.
   • Database queries should not take longer than 2 seconds to execute under normal conditions.

2. Scalability

   • The system should be able to handle an increase in user load by 50% without any degradation in performance.
   • The system must support upscaling to accommodate additional 1,000 users without significant changes in infrastructure.

3. Reliability

   • The system should have an uptime of 99.9%.
   • Automated failover to a backup server should occur within 1 minute in case of a server failure.

4. Usability

   • The user interface must be accessible, adhering to the WCAG 2.1 AA standards.
   • New users should be able to complete basic tasks without referring to user documentation.

5. Security

   • All user data must be encrypted using at least AES 256-bit encryption.
   • The system must comply with GDPR for all users from the European Union.

6. Maintainability

   • The system should be built using clear coding standards to ensure it is easy to update and maintain.
   • Any bugs identified should be fixable within 48 hours for critical issues.

7. Portability

   • The application should be operable on both Windows 10 and macOS X without any modifications.
   • The mobile app must function correctly across the latest versions of iOS and Android.

Conclusion

Functional requirements are about the "what" of the system—what the system should do, while non-functional requirements are about the "how"—how the system performs tasks and meets other criteria like usability and reliability. Both are crucial for the design and development of a robust, user-centered software system that meets all stakeholder expectations.