When building a software system, requirements are usually classified into two main categories:
🛠️ Functional Requirements
Definition: Functional requirements specify what the system should do. They describe the core features, functions, and behaviors of the system.
Examples:
- A user can register with their email and password.
- The system should send a confirmation email after registration.
- The admin can delete user accounts.
- The search bar should return results based on keywords.
These are user-facing behaviors or operations that define how the system reacts to inputs.
🧱 Non-Functional Requirements
Definition: Non-functional requirements describe how the system performs under certain conditions. They are about quality attributes like performance, security, reliability, usability, etc.
Examples:
- The system should load the dashboard within 2 seconds (Performance).
- The system must support up to 10,000 concurrent users (Scalability).
- All user data should be encrypted in transit and at rest (Security).
- The app should have 99.9% uptime (Reliability).
- The UI should be mobile-friendly and accessible (Usability).
These are not directly related to a specific function but rather to the overall system behavior.
🎯 Key Differences
| Feature | Functional Requirements | Non-Functional Requirements |
|---|---|---|
| Focus | What the system should do | How the system should perform |
| Examples | Login, search, upload image | Performance, security, usability |
| Direct User Interaction | Yes | Often indirectly noticed |
| Measurable By | Pass/fail test cases | Metrics (e.g., response time, uptime) |
| Type of Requirement | Business logic/features | System attributes or quality factors |
✅ Conclusion
Functional requirements define what a system should do, while non-functional requirements define how well it should perform. Both are crucial for delivering a complete and reliable software product.
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