Non-Functional Requirements in Software Engineering - GeeksforGeeks (2024)

Non-functional requirements in software engineering refer to the characteristics of a software system that are not related to specific functionality or behavior. They describe how the system should perform, rather than what it should do. This article focuses on discussing non-functional requirements in detail.

What are Non-Functional Requirements?

Non-functional requirements are the constraints that specify the quality attribute of the software.

1. Non-functional requirements deal with scalability, maintainability, performance, portability, security, reliability, and many more.
2. They are important because they can significantly impact the overall quality and success of a software system.
3. They also help ensure the system is maintainable, portable, and compliant with relevant laws and regulations.
4. They help to ensure that the system responds quickly to user actions within acceptable time frames.
5. They ensure system is easy-to-use and accessible.
6. They defines system uptime and downtime, ensuring that it is reliable and available when required.

Types of Non-Functional Requirements

1. Performance Requirements

Performance requirements describe the expected performance of the software system, such as its response time, throughput, and resource utilization. The software system should perform efficiently under different conditions and loads.

• Response Time: It indicates the longest period that the system will allow to react to a user’s request.
• Throughput: The quantity of transactions or processes that the system should be able to process in a specific amount of time is known as throughput.
• Scalability: It defines how well the system can add resources to accommodate a growing workload or user base.

Example: A requirement that the system should be able to handle a certain number of concurrent users or process a certain amount of data within a specific time frame.

2. Reliability Requirements

Reliability requirements describe the ability of the software system to perform its functions consistently and accurately over time.

Example: The system shall have an uptime of 99.99% manually.

3. Scalability Requirements

Scalability requirements indicate the system’s ability to grow in data volume and user load. The system must remain stable and maintain performance with more users, data, business processes, or modules.

Example: The system shall support up to 20,000 concurrent users without the degradation of performance.

4. Availability Requirements

Availability requirements define the system’s operational continuity and the system should be available and responsive when needed, and should not experience frequent failures or crashes.

Example: The system shall be available 24×7 excluding the maintenance window.

5. Usability Requirements

Usability requirements describe the ease of use and user-friendliness of the software system. The system should be easy to navigate and understand and should provide clear and concise feedback to the user.

Example: New users shall be able to complete the registration process within 10 minutes.

6. Security Requirements

Security requirements describe the measures taken to protect the software system from unauthorized access, attacks, and data breaches. The system should be secure and protect the privacy and confidentiality of its users.

• Authentication: The process by which users are validated and given access to the system is known as authentication.
• Authorization: It establishes the access levels and permissions for various user roles.
• Data Encryption: Itrefers to the techniques and formulas used to protect private information both during transmission and storage.

Example: The system shall use multi-factor authentication for all user logins.

7. Maintainability Requirements

Maintainability requirements describe the ease with which the software system can be modified, updated, and maintained over time. The system should be designed with modularity and extensibility in mind and should be easy to test and debug.

Example: The system’s codebase should be compliant with the coding standards to ensure maintainability.

8. Efficiency Requirements

Efficiency requirements explain how to use resources like CPU, memory,and network trafeffectivelynner. It indicates the requirement for performance optimization in particular use cases or scenarios.

Example: The system shall not exceed 75% CPU utilization under peak load.

9. Portability Requirements

Portability requirements define if the system can work in different environments. It establishes how well the actions performed via one platform can be executed in another.

Example: The application shall be able to execute on both Windows and Linux operating systems without modification.

10. Reusability Requirements

Reusability requirements indicate how much of the system components can be reused in another system.

Example: The system’s login and authentication module can be reusable across multiple applications.

Functional vs Non-Functional Requirements

Here are some of the differences between functional and non-functional requirements:

Benefits of Identifying Non-Functional Requirements

1. Improved System Quality: By specifying non-functional requirements, engineers can ensure that the system will have desired characteristics such as performance, security, usability, reliability, maintainability, portability, and compliance, which can improve the overall quality of the system.
2. Increased User Satisfaction: By ensuring that the system has good usability and meets the user’s performance and security expectations, engineers can increase user satisfaction with the system.
3. Better Alignment with Business Goals: By aligning non-functional requirements with the business goals, engineers can ensure that the system supports the overall objectives of the organization and meets the expectations of the stakeholders.
4. Reduced Rework: By identifying and addressing non-functional requirements early on in the development process, engineers can reduce the likelihood of costly rework later on.
5. Improved System Scalability and Adaptability: By specifying non-functional requirements related to scalability and adaptability, engineers can ensure that the system can handle a growing number of users or changing business needs.
6. Improved Compliance: By specifying non-functional requirements related to compliance, engineers can ensure that the system adheres to relevant laws, regulations, industry standards, or company policies.
7. Better System Maintenance: By specifying non-functional requirements related to maintainability, engineers can ensure that the system is easy to maintain, test, and debug, which can save time and cost in the long run.

Challenges of Identifying Non-Functional Requirements

1. Difficulty in Identifying All Requirements: It can be difficult to identify all the non-functional requirements, especially when dealing with complex systems or new technologies.
2. Difficulty in Predicting Future Requirements: It can be difficult to predict future non-functional requirements, which can result in the software becoming outdated or needing to be redesigned.
3. Difficulty in Measuring and Testing: Non-functional requirements can be difficult to measure and test, which can make it challenging to ensure that they have been met.
4. Time-consuming: Gathering and specifying non-functional requirements can be time-consuming, which can slow down the development process.
5. Costly: Identifying, specifying, and implementing non-functional requirements can be costly, especially when involving multiple stakeholders.
6. Risk of Changing Requirements: Non-functional requirements may change over time, which can lead to confusion and require additional work to keep the project aligned with the updated requirements.
7. Conflicting Requirements: Non-functional requirements may be in conflict with each other and it can be difficult to balance them and prioritize which one to implement.
8. Unforeseen Requirements: Non-functional requirements may not be fully identified during the requirement-gathering phase, and some requirements may only be discovered after the system has been deployed.

Best Practices to Document Non-Functional Requirements

Here are some best practices that can be followed for documenting non-functional requirements:

1. Be Clear: Define non-functional requirements in clear, precise, and quantifiable terms.
2. Avoid Ambiguous Terminology: Avoid ambiguity by using clear and consistent terminology while documenting non-functional requirements.
3. Align with Business Goals: Ensure that non-functional requirements are aligned with the overall business objectives and user expectations.
4. Prioritize Requirements: Prioritize and rank requirements based on what impact they will have on the system.
5. Collaborate with Stakeholders: Collaborate with stakeholders including developers, end users, and business analysts, to gather a detailed and comprehensive set of requirements.

Conclusion

Non-functional requirements are a critical aspect of software engineering that describes the qualities and characteristics of the software system beyond its functional requirements. These requirements ensure that the software system meets the expectations of its users and stakeholders and performs efficiently and reliably under different conditions and loads.

FAQs related to Non-Functional Requirements in Software Engineering

1. Why are non-functional requirements important?

Non-functional requirements are important as they makes sure that the system meets quality standards like performance, security, usability, etc, which are important for customer satisfaction.

2. How to measure non-functional requirements?

Non-functional requirements can be measured using metrics such as response time, error rates, uptime, and throughput.

3. Who is responsible for defining non-functional requirements?

Defining non-functional requirements requires collaboration between stakeholders, including business analysts, developers, end-users, and architects.