10 Differences Between functional and non functional requirments

Understanding the Difference Between Functional and Non-Functional Requirements

What are Functional Requirements?

Functional requirements describe what the system should do and its behavior in response to specific inputs. These requirements focus on the functionality of the system and are typically related to the actions, tasks, and operations that the system must perform to meet its intended purpose.

Examples of Functional Requirements:

1. The user should be able to log in using their username and password.
2. The system should allow users to add items to their shopping cart.
3. The application must be able to generate monthly reports based on the entered data.
4. The website should provide a search functionality to allow users to find specific products.
5. The software must be able to send confirmation emails to users after a successful transaction.

Uses of Functional Requirements:

Functional requirements ensure that the system performs the tasks it was designed for. They are crucial for developers to understand what is expected from the system and guide the design and development process accordingly.

What are Non-Functional Requirements?

Non-functional requirements specify the quality attributes and constraints of the system, focusing on how the system should behave and perform, rather than what it should do. These requirements address aspects such as performance, usability, reliability, security, and scalability.

Examples of Non-Functional Requirements:

1. The system must respond to user interactions within 2 seconds.
2. The user interface should be intuitive and user-friendly.
3. The system should be available 24/7 with minimal downtime for maintenance.
4. The application should be able to handle concurrent user requests without performance degradation.
5. The system must ensure data privacy and comply with relevant security standards.

Uses of Non-Functional Requirements:

Non-functional requirements are crucial for ensuring that the system meets the user’s expectations in terms of performance, usability, and security. They help evaluate the overall quality of the system and guide decisions related to architecture, design, and testing.

Differences Between Functional and Non-Functional Requirements:

Difference Area Functional Requirements Non-Functional Requirements
Focus What the system should do How the system should perform
Nature Action-oriented Quality-oriented
Scope Specific features and tasks Overall system behavior
Verifiability Can be objectively tested Can be evaluated subjectively
Change frequency Less frequent More frequent
Measurability Quantitative Qualitative
Prioritization Can be prioritized based on business value Can be prioritized based on criticality
Dependencies Functional requirements might have dependencies on each other Non-functional requirements might impact multiple functionalities
Testing Functionality testing Performance testing, usability testing, security testing, etc.
Documentation Functional requirements are documented in User Stories, Use Cases, etc. Non-functional requirements are documented in Quality Attribute Scenarios, Constraints, etc.


Functional requirements define what the system should do, while non-functional requirements define how it should perform. Functional requirements address specific tasks and features, while non-functional requirements focus on quality attributes and constraints. Both types are crucial for the successful development and evaluation of a system.

People Also Ask:

What is the importance of functional and non-functional requirements?

Functional requirements ensure that the system performs the tasks it was designed for, while non-functional requirements ensure its overall quality attributes and constraints are met.

Can functional and non-functional requirements coexist?

Yes, functional and non-functional requirements coexist and complement each other in defining and evaluating a system’s behavior and performance.

How are functional requirements different from business requirements?

Business requirements define the high-level goals and objectives of the system, while functional requirements specify the specific tasks and functionality necessary to achieve those goals.

What happens if functional requirements are not met?

If functional requirements are not met, the system may not perform the intended tasks, leading to a less functional or even useless system.

Can non-functional requirements outweigh functional requirements?

Sometimes non-functional requirements can outweigh functional requirements, especially if the system’s performance, security, or usability are critical to its success.

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