In software development, there are two main categories of requirements: functional and non-functional. Functional requirements describe what the software must do, while non-functional requirements describe how the software must perform.
Functional requirements are the most obvious type of requirement. They describe the features that the software must have in order to meet the needs of the users. For example, a functional requirement for a banking application might be that it must allow users to deposit and withdraw money from their accounts.
Functional requirements are typically expressed in terms of the following:
- Features: The features that the software must have in order to meet the needs of the users.
- Behavior: The way that the software must behave in order to meet the needs of the users.
- Data: The data that the software must store and process in order to meet the needs of the users.
Non-functional requirements are less obvious, but they are just as important. They describe the qualities that the software must have in order to be successful. For example, a non-functional requirement for a banking application might be that it must be secure.
Non-functional requirements are typically expressed in terms of the following:
- Performance: The speed, response time, and resource usage of the software.
- Security: The ability of the software to protect its data from unauthorized access.
- Usability: The ease with which users can learn how to use the software.
- Reliability: The ability of the software to perform its functions without errors.
- Maintainability: The ease with which the software can be modified and updated.
- Portability: The ability of the software to be used on different platforms.
Relationship Between Functional and Non-Functional Requirements
Functional and non-functional requirements are usually interrelated. For example, the security of a banking application is related to its ability to allow users to deposit and withdraw money from their accounts.
It is important to track the dependencies between functional and non-functional requirements. This can be done using a requirements management system. A requirements management system is a tool that helps software developers to track and manage the requirements for a software project.
The importance of functional and non-functional requirements cannot be overstated. They are essential for ensuring that the software meets the needs of the users and that it is successful. Challenges arise as developers grapple with NFR considerations. Caution is warranted as they may overlook relevant NFRs or design ones that are less applicable to the product's stage.