Functional vs. Nonfunctional

Attribute	Functional	Nonfunctional
Definition	Describes what the system should do	Describes how the system should perform
Focus	Emphasizes on the behavior of the system	Emphasizes on the performance of the system
Measurability	Can be easily measured and tested	Can be difficult to measure and test
Examples	User authentication, data validation	Response time, scalability

Definition

Functional and nonfunctional are two key terms in the world of software development. Functional requirements refer to the specific actions that a system must be able to perform, such as calculations, data manipulation, and other specific tasks. Nonfunctional requirements, on the other hand, are the qualities that a system must possess, such as performance, security, usability, and scalability.

Focus

Functional requirements focus on what the system should do, while nonfunctional requirements focus on how the system should perform. Functional requirements are typically more concrete and specific, as they outline the exact features and functions that the system must have. Nonfunctional requirements, on the other hand, are more abstract and subjective, as they deal with the overall quality and performance of the system.

Measurability

Functional requirements are generally easier to measure and test, as they can be validated through specific test cases and scenarios. Nonfunctional requirements, on the other hand, are often more difficult to measure, as they are subjective and can vary depending on the user's perspective. For example, while it is easy to test whether a system can perform a specific calculation, it is much harder to measure the system's overall usability or performance.

Importance

Both functional and nonfunctional requirements are important in the development of a software system. Functional requirements ensure that the system meets the needs of the users and performs the necessary tasks. Nonfunctional requirements, on the other hand, ensure that the system meets the necessary quality standards and performs well under various conditions. Neglecting either type of requirement can lead to a system that does not meet the needs of the users or fails to perform adequately.

Flexibility

Functional requirements are typically more rigid and specific, as they outline the exact features and functions that the system must have. Nonfunctional requirements, on the other hand, are often more flexible and can be adjusted based on the specific needs of the system. For example, while a system may have strict functional requirements for performing calculations, the nonfunctional requirements for performance may be more flexible and allow for variations based on the system's usage.

Interdependence

Functional and nonfunctional requirements are closely interdependent in the development of a software system. Functional requirements drive the development of the system's features and functions, while nonfunctional requirements ensure that the system meets the necessary quality standards. For example, while a system may have all the necessary features to perform a specific task, it may fail to meet the necessary performance standards outlined in the nonfunctional requirements.

Conclusion

In conclusion, functional and nonfunctional requirements are both essential in the development of a software system. Functional requirements focus on what the system should do, while nonfunctional requirements focus on how the system should perform. Both types of requirements are important for ensuring that the system meets the needs of the users and performs well under various conditions. By understanding the differences between functional and nonfunctional requirements, software developers can create systems that are both functional and high-quality.