What is a Non-Functional Requirement?
Nonfunctional Requirements define how the system works. Non-Functional requirements describe the system's overall behavior, like robustness, scalability, and maintainability. A simple definition of a Non-functional requirement is any requirement that specifies the overall behavior of the system is called a non-functional requirement. Non-functional requirements are significant because they can make or break the success of a software system or a product.
Even if a system satisfies all expected functional requirements, users will not hesitate to reject it outright if it fails to produce the desired quality results.
Many functional needs that are extremely important and need to be expressed in the proper amount of detail in the requirements papers are derived from non-functional requirements.
Additionally, they play a crucial role in several important architectural decisions and ensure that important design considerations are made early rather than when costs and the risk of modification are higher.
A Non-Functional Requirement (NFR) is a requirement in software and system development that specifies criteria for the system's performance, behavior, and qualities rather than defining specific features or functionalities. Unlike Functional Requirements, which describe what the system should do, Non-Functional Requirements describe how the system should perform or behave.
Non-Functional Requirements are essential for ensuring that the software or system meets certain quality attributes and provides a satisfactory user experience. These requirements are typically not directly visible to end-users but are crucial for the project's overall success.
Some of the Non-Functional Requirements are
- Performance
- Scalability
- Capacity
- Availability
- Reliability
- Recoverability
- Maintainability
- Serviceability
- Security
- Regulatory
- Data Integrity
- Usability
- Interoperability.
Examples of Non-Functional Requirements
- Performance: Specifies how fast the system should respond to user interactions or how much load it can handle. For instance, response time, throughput, or scalability.
- Reliability: Describes how dependable and stable the system should be. It may include metrics such as the mean time between failures (MTBF) or the mean time to repair (MTTR).
- Security: Outlines the security measures the system needs to implement, like access controls, data encryption, and protection against various attacks.
- Usability: Defines the ease of use and user-friendliness of the system. It may cover aspects such as accessibility, user interface design, and user experience (UX).
- Maintainability: Addresses how easy it is to maintain and modify the system after deployment. It includes factors like code readability, modularity, and documentation.
- Capability: Refers to the system's ability to handle increasing amounts of data, users, or traffic without a significant drop in performance.
- Availability: Specifies the time the system should be available for use. It may include uptime requirements and planned maintenance windows.
- Compatibility: Describes the extent to which the system should work with various hardware, software, and network environments.
- Compliance: Ensures the system adheres to legal, regulatory, and industry standards.
- Interoperability: Addresses the system's ability to interact and integrate with other systems and services.
Non-Functional Requirements are crucial for providing a comprehensive understanding of the system's expected behavior and performance, guiding the development team to build a high-quality product that meets the stakeholders' needs and expectations.
Some More Details
Availability
The degree of a solution's operability and accessibility at a given time is called availability. It is a time during which the system is completely operational, i.e., accessible for usage, and it is occasionally included as a service level agreement due to the importance of the system to the company.
Aspects of availability that need to be considered during elicitation include—but are not limited to periods during which availability is essential to achieve business objectives, the effects of a system's downtime, scheduled maintenance windows, and notifications during a system outage.
Interoperability/Compatibility
The level of interoperability indicates how well the solution works with other parts. It is a gauge of how well the system works with other software programmers and how simple it is to interact with other hardware.
Performance
Performance is the degree to which a solution or a part of it carries out its functions while using the fewest resources possible. Due to its significant design consequences and influence on hardware device selection, it is a significant quality attribute.
Reliability
A solution or one of its components must be reliable to carry out its intended functions under predetermined circumstances for a predetermined amount of time.
Reliability may be defined by the average number of cycles a system runs before failing, the percentage of successfully performed operations over time, the maximum allowable failure probability, or the total number of failures over time.
During elicitation, reliability-related topics will be covered, including but not limited to the evaluation of the system as reliable, reliability categorization that distinguishes between occasional failures and regular failures, and the effect of failure on business activities.
Usability
Usability refers to how easily a user can pick up utilizing the solution and how easily he or she can use the system. Usability encompasses a variety of factors in addition to ease of learning and usage, such as memory ease, error avoidance & handling, and accessibility, among others.
The number of human-system touchpoints necessary to complete a task, the average time required to complete a task, the average number of errors made during task completion, the average number of attempts before a task is completed, and other factors related to usability will all be discussed during the elicitation process.
Maintainability/Modifiability
The term "maintenance-friendliness" describes how easily a solution or part of it may be mended, improved to suit business needs, boost productivity, or adjusted to a changing environment.
It represents how simple it is to comprehend, modify, and extend the software architecture and code. Maintainability is crucial for systems that must be routinely modified or improved. The percentage of patches made right the first time, the percentage of changes deployed correctly the first time, and the typical amount of time needed to repair a problem correctly are among the maintainability aspects to be reviewed during elicitation.
Portability
The capacity to move a system or one of its components from one operating environment to another is known as portability. Its significance has grown over time as a result of the need for apps to function across several environments, including Windows, Mac, and Linux, as well as mobile operating systems like Android and iOS.
During elicitation, portability issues will be raised concerning, but not limited to, various platforms on which the system must run, system components, and/or data pieces that must be explicitly developed for greater portability.
Scalability
Scalability is a term used to describe how well a solution can change over time to accommodate growing workloads. The user base, transactions, data, network traffic, or other reasons may have increased the workload.
The system should be able to scale up, which may entail adding more servers, faster processors, more disc space, or more network capacity to the hardware or utilizing software-specific techniques like data compression, code and performance optimization, and other similar methods.
Reusability
The ability of software or a software component to be reused in various applications is referred to as reusability. Which system elements/components should be developed in a way that enables their reuse across different applications must be defined?
Aspects of reuse that will be discussed during elicitation include but are not limited to functionality or artifacts from other applications that can be used across applications that are being built, as well as functionality or artifacts from the application that is being built that can be used across other applications, either current or future.
Importance Non-Functional Requirements
Non-functional requirements are significant because they can make or break the success of a software system or a product. Even when a system satisfies all expected functional criteria but fails to produce the desired quality results, users will not hesitate to reject it outright.
Conclusion
Users frequently expect how well a software system should function in terms of availability, usability, speed of functional execution, the likelihood of failure, security against unauthorized access, and effectiveness in handling unforeseen circumstances when they do arise.