Non-Functional Requirements: Definition and Examples

When it comes to developing successful software systems, it’s not just about the functionality. Non-functional requirements play a vital role in shaping a product’s overall quality, usability, and performance. While functional requirements define what a system should do, non-functional requirements focus on how it should perform, ensuring it meets the desired standards and expectations.

What are Non-Functional Requirements?

Non-functional requirements encompass various aspects, such as reliability, performance, security, scalability, usability, and maintainability. They are guiding principles to ensure the system functions effectively and provides a seamless user experience. For instance, reliability ensures the system operates consistently without failures or errors. 

At the same time, performance focuses on speed, responsiveness, and efficiency. Security addresses the protection of sensitive data and safeguards against unauthorized access. At the same time, scalability enables the system to handle increasing loads and growing user demands. Usability emphasizes the system’s ease of use and intuitiveness. 

At the same time, maintainability ensures that the system can be updated, repaired, and enhanced without excessive effort.

By defining and prioritizing non-functional requirements, stakeholders can establish clear expectations and objectives for the system. This not only aids in effective decision-making during the development process but also lays a solid foundation for future growth and enhancements. 

Non-functional requirements enable teams to consider essential factors beyond functionality, ensuring the system is reliable, performant, secure, and user-friendly.

Types of Non-Functional Requirements

Here are some types of non-functional requirements (NFRs)

• Performance: This type of NFR specifies how well the system will perform. It includes factors such as speed, response time, and throughput. For example, a performance NFR might state that the system must be able to process 1000 transactions per second.

• Scalability: NFR specifies how well the system can handle the increased load. It includes factors such as the number of users, the amount of data, and the number of transactions. For example, a scalability NFR might state that the system must be able to handle 10000 users without any degradation in performance.

• Reliability: In this case, NFR specifies how often the system will fail. It includes factors such as mean time to failure (MTTF), mean time to repair (MTTR), and availability. For example, a reliability NFR might state that the system must be available 99.9% of the time.

• Security: here, NFR specifies how well the system is protected from unauthorized access, modification, or destruction. It includes factors such as authentication, authorization, and encryption. For example, a security NFR might state that the system must use strong encryption to protect sensitive data.

• Usability: In this type, NFR specifies the system’s ability to use. It includes learnability, efficiency, memorability, error tolerance, and user satisfaction. For example, a usability NFR might state that the system must be easy to learn and use by users without prior experience.

• Maintainability: NFR specifies how easy the system is to change and update. It includes factors such as modularity, documentation, and testability. For example, a maintainability NFR might state that the system must be easy to change by developers with no prior experience.

• Portability: This type of NFR specifies how easily the system moves to a new environment. It includes factors such as platform independence, configuration management, and documentation. For example, a portability NFR might state that the system must be able to run on Windows, Linux, and macOS.

These are just some of the most common types of non-functional requirements. There are many other NFRs, and the specific NFRs relevant to a particular system will vary depending on the system’s purpose and environment.

How to Write Non-Functional Requirements

Now let us understand and discuss some tips for writing non-functional requirements efficiently.

• Use clear and concise language. Your language should be easy to understand for both technical and non-technical audiences. Avoid using jargon or acronyms that your audience may not be familiar with.

• Be specific and measurable. NFRs should be clear enough that they can be measured. For example, instead of saying, “The system must be secure,” you could say, “The system must have a security rating of at least 95%.”

• Prioritize the NFRs. Not all NFRs are created equal. Some NFRs are more critical than others. It is crucial to prioritize the NFRs so the development team can focus on the most important ones first.

• Refer to the system architecture when possible. If you have a system architecture, you can use it to help you write NFRs. For example, if your system architecture specifies that the system will be distributed, you could write an NFR that stipulates that the system must be able to handle network failures.

• Use a consistent format. This will make it easier for the development team to understand and implement the NFRs.

Here is an example of a well-written NFR:

NFR: The system must handle 10000 users without any degradation in performance.

Explanation: This NFR is clear, concise, specific, measurable, and prioritized. It is also consistent with the system architecture, which specifies that the system will be distributed.

Benefits of Non-Functional Requirements

Lets now shed some light on the benefits of non-functional requirement,

• Quality improves: NFRs can help enhance a software system’s quality by ensuring that the system meets the needs of its users and stakeholders. For example, an NFR that specifies that the system must be secure can help to prevent unauthorized access to the system.

• Risk reduction: NFRs can reduce the risk of failure by ensuring that the system is designed and implemented to meet the specific requirements of its environment. For example, an NFR specifying that the system must handle increased load can help prevent the system from crashing under heavy traffic.

• Increase in efficiency: These can increase the efficiency of a software system by ensuring that the system is designed and implemented to be as efficient as possible. For example, an NFR specifying that the system must be able to process 1000 transactions per second can help ensure that the system can handle the demands of its users.

• Better communication: NFRs can improve stakeholder communication in developing a software system. For example, an NFR that specifies that the system must be easy to use can ensure that the developers and users are on the same page.

• Better satisfaction: NFRs can increase the satisfaction of the users of a software system by ensuring that the system meets their needs and expectations. For example, an NFR that specifies that the system must be available 99.9% of the time can help ensure that the users of the system can access the system when they need it.

Best Practices for Handling Non-Functional Requirements

• Stakeholder Involvement: Engage stakeholders from different roles and perspectives to comprehensively understand non-functional requirements. This collaboration ensures that the needs and expectations of all stakeholders are considered.

• Clear Definition and Prioritization: Clearly define and prioritize non-functional requirements based on their impact and importance. This helps in focusing efforts on critical aspects and avoiding unnecessary complexities.

• Quantifiable Metrics: Establish measurable metrics to measure and evaluate non-functional requirements whenever possible. This enables objective assessment and system performance verification against the defined criteria.

• Collaboration Across Teams: Foster collaboration and communication between different teams, including developers, testers, designers, and business analysts. This interdisciplinary approach ensures that non-functional requirements are addressed holistically and integrated seamlessly into the development process.

• Industry Standards and Best Practices: Stay updated with industry standards, frameworks, and best practices related to non-functional requirements. These resources provide valuable guidance and insights for handling security, performance, and usability.

• Continuous Validation and Testing: Regularly validate and test the system against non-functional requirements throughout the development lifecycle. This helps identify gaps or deviations early on and allows for timely adjustments or improvements.

• Flexibility and Adaptability: Non-functional requirements may evolve or change over time. Embrace a flexible and adaptive mindset to accommodate new needs, emerging technologies, and changing user expectations.

• Documentation and Traceability: Maintain comprehensive documentation of non-functional requirements, their rationale, and any changes made. This documentation ensures clarity, facilitates knowledge sharing, and helps with future enhancements or maintenance.

• User-Centric Approach: Keep the end-user in mind when defining and prioritizing non-functional requirements. Focus on delivering a seamless user experience by considering usability, accessibility, and performance.

• Regular Reviews and Feedback: Conduct regular reviews and seek feedback from stakeholders to assess the effectiveness of non-functional requirements. This iterative approach allows for continuous improvement and refinement.

By following these best practices, organizations can effectively handle non-functional requirements and ensure the development of high-quality software systems that meet the desired standards and user expectations.

Conclusion

In the end, non-functional requirements are crucial components that ensure a software system’s overall quality, performance, and user experience. They go beyond the system’s basic functionality. 

Organizations may create software solutions that exceed functional requirements and excel in critical areas influencing user satisfaction and system success by identifying and addressing factors including stability, security, scalability, usability, and maintainability. 

Additionally, organizations may create the framework for developing reliable, effective, and user-friendly systems that stand the test of time and improve the overall user experience by taking non-functional needs into account from the start and putting best practices into practice.