What is the Difference Between Functional and Non Functional Requirements?

The main difference between functional and non-functional requirements lies in their description of a system or software. Functional requirements describe what the system should do, while non-functional requirements describe how the system should perform. Here are some key differences between the two:

Functional Requirements:

1. Define the system or its components' functions.
2. Specify "What should the software system do?".
3. Captured in use cases.
4. Mandatory for the system to work.
5. Examples include user flows, features, and functions that developers must implement to enable users to accomplish their tasks.

Non-Functional Requirements:

1. Define the quality attributes of a software system.
2. Place constraints on "How should the software system work?".
3. Captured as quality attributes.
4. Not mandatory, but essential for user satisfaction and system performance.
5. Examples include performance, usability, security, and maintainability.

In summary, functional requirements outline the features and functions that a system must have, while non-functional requirements describe the system's performance, usability, and other quality attributes. Both types of requirements are essential for a well-performing system, as functional requirements define the system's functionality, and non-functional requirements detail how the system should be usable and efficient.

Comparative Table: Functional vs Non Functional Requirements

Functional and non-functional requirements are two types of criteria used to define a system or its components. Here is a table summarizing the main differences between them:

Functional requirements explain the characteristics that a system is expected to have and the way it should behave. They are represented or stated in the form of input to be given to the system, the operation performed, and the output expected. On the other hand, non-functional requirements place constraints on the quality attributes of a software system, such as reliability, maintainability, and performance. They describe the general properties of a system and are also known as quality attributes. Both types of requirements are essential for a usable system.