Difference Between Functional and Nonfunctional Requirements
When developing a software or a system, it is important to understand the requirements that need to be fulfilled. There are two types of requirements to be taken into consideration- functional and nonfunctional requirements. These requirements differ in terms of their purpose, scope and how they affect the end user experience. In this article, we will discuss the difference between functional and nonfunctional requirements.
Functional Requirements
Functional requirements are the specifications that describe the functions that the software or system must perform. These requirements focus on what the system should do and how it should do it. Functional requirements outline the key features and functionality that the system must have. They include things like creating user accounts, generating reports, and sending notifications. They describe the features that are needed to achieve the end goal.
Functional requirements are specific and measurable. They can be tested to ensure that they meet the desired functionality. They outline the expected outcomes, which are the things that the software should be able to do. They are critical for the system to be useful and for it to satisfy the user’s needs.
Nonfunctional Requirements
Nonfunctional requirements, on the other hand, focus on how the system should perform. They are the requirements that describe the characteristics that the system must exhibit. Nonfunctional requirements are often referred to as quality or performance requirements. They include things like system performance, reliability, usability, and security.
Nonfunctional requirements are not the features that the system must offer, but how these features should be delivered. These requirements are broadly defined and help to ensure that the software or system developed is of high quality.
The Importance of Understanding the Difference
It is essential to understand the difference between functional and nonfunctional requirements when developing software or a system. This is because fulfilling one type of requirement at the expense of the other can lead to an unsatisfied user experience. For instance, developing a software system that has all the desired features (functional requirements), but not properly securing it (nonfunctional requirements) can lead to cyber-attacks and other security-related issues.
In conclusion, functional and nonfunctional requirements play crucial roles in the development of software and systems. Knowing the difference between these two types of requirements is necessary to ensure that both the desired functionality and characteristics of the system are fulfilled. While functional requirements dictate what the software or system should do, nonfunctional requirements outline how it should be done. By meeting both requirements, software and systems can be developed to meet the needs and satisfaction of the user.
Table difference between functional and nonfunctional requirements
| Functional Requirements | Nonfunctional Requirements |
|---|---|
| Defines the specific tasks that the system must be able to perform. | Defines the performance criteria that the system must adhere to. |
| Related to the behavior of the system and what it should do. | Related to the quality attributes of the system, such as usability, reliability, performance, security, and maintainability. |
| Easily testable and verifiable. | May not be directly testable, but can be evaluated through metrics or other means. |
| Usually expressed in terms of features and capabilities. | Usually expressed as constraints or criteria that the system must meet. |
| Functional requirements can be derived from user stories. | Nonfunctional requirements can be derived from stakeholder needs and expectations. |