Function Requirement vs. Non-Functional Requirement

Attribute	Function Requirement	Non-Functional Requirement
Definition	Specifies what the system should do	Specifies how the system should perform
Focus	Functionality	Performance, usability, reliability, etc.
Measurability	Can be easily measured	May be subjective and harder to measure
Implementation	Directly implemented in the system	Guidelines for system behavior

Definition

Function requirements are the specific functions or capabilities that a system must perform in order to meet the needs of its users. These requirements are typically described in detail and are often the basis for the design and development of a system. Non-functional requirements, on the other hand, are the qualities or attributes that a system must have in order to be considered successful. These requirements are not related to specific functions, but rather focus on aspects such as performance, security, and usability.

Importance

Function requirements are essential for ensuring that a system meets the needs of its users and performs the necessary tasks. Without clear function requirements, it can be difficult to determine whether a system is meeting its objectives. Non-functional requirements, on the other hand, are important for ensuring that a system is reliable, secure, and efficient. These requirements help to define the overall quality of a system and are crucial for its success.

Scope

Function requirements typically focus on the specific features and functions that a system must have in order to meet the needs of its users. These requirements are often detailed and specific, outlining exactly what the system should be able to do. Non-functional requirements, on the other hand, are broader in scope and focus on the overall quality and performance of a system. These requirements are not tied to specific functions, but rather apply to the system as a whole.

Measurability

Function requirements are often easily measurable, as they are specific tasks or functions that can be tested and verified. For example, a function requirement might specify that a system must be able to process a certain number of transactions per second. Non-functional requirements, on the other hand, can be more difficult to measure, as they are often qualitative in nature. For example, a non-functional requirement might specify that a system must be user-friendly, which can be subjective and open to interpretation.

Dependencies

Function requirements are often dependent on each other, as they are specific tasks or functions that must work together to achieve the overall objectives of a system. For example, a system may need to have a login function in order to access certain features. Non-functional requirements, on the other hand, are often independent of each other and can be implemented separately. For example, a system may need to be both secure and user-friendly, but these two requirements can be addressed independently of each other.

Flexibility

Function requirements are typically less flexible than non-functional requirements, as they are specific tasks or functions that must be performed in a certain way. Changing function requirements can often require significant changes to the design and development of a system. Non-functional requirements, on the other hand, are often more flexible and can be adjusted without impacting the core functions of a system. For example, a system may need to be able to handle a certain number of users, but the specific performance requirements can be adjusted as needed.

Conclusion

In conclusion, function requirements and non-functional requirements play different but equally important roles in the development of a system. Function requirements focus on the specific tasks and functions that a system must perform, while non-functional requirements focus on the overall quality and performance of a system. Both types of requirements are essential for ensuring that a system meets the needs of its users and is successful in achieving its objectives.