Question

Briefly explain what is meant by “non-functional requirements” and why they are documented separately from the functional requirements.

Answer 1

Non Functional Requirements describes the general characteristics of a system. They specifies the systems behaviour . They can be considered as the quality attributes of a system.

Some of the Non Functional Requirements are:

Usability: describes how system will be used by different people or in different circumstances. It also describes how difficult the system will be to learn and operate for a user. Example:

• Whether the system will be usable for color blind people.
• Whether the system can be operated in different country -different currency, different time zone, different language

.Reliability : describes how much users can rely on the system even during failure. Example:

• How quickly the system can be recovered during failure.
• Whether the system provides services when needed.
• Whether the system can withstand attacks.

Performance: describes how the system responds to various users interaction . Example:

• Time taken by the system to respond during stress(heavy load) period.
• Whether the system is able to support specified number of users/transactions at a time.

Security : ensures that the system's data is protected from any unauthorized access.

• Correct data is maintained by the system.
• The system is keeping the private data secured.

Maintainability : describes that the system can be upgraded without any negative impact on its performance. Example:

• System's ability to change some component without affecting others.
• The system can be investigated for a failure.

Non functional requirements are documented separately from the functional requirements because:

• Non functional requirements specifies the properties of the software as a whole while functional requirement specifies the functionality that the system should provide.
• Non functional requirements describes how the system performs some function, while functional requirement describes what function the system does.
• The nonfunctional requirements provide limitations/constraints on how the functional requirements are to be designed and implemented.

By separating non functional and functional requirements , the designers can clearly identify the features from the constraints and limitations.