Difference Between Functional and Non Functional Requirements

Requirements can be divided mainly into functional and non functional requirements. But are you aware of the difference between functional and non functional requirements? If not, then don’t worry. This article will discuss the difference between functional and non functional requirements in great detail.

In general, the main difference between functional and non functional requirements is that functional requirements define the core functionality of a system. In contrast, non functional requirements define how that functionality is delivered.

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Before we dive deeper into the difference between functional and non functional requirements, let’s go through the list of topics that we will cover in this article.

Table of Contents (TOC)

• Difference Between Functional and Non Functional Requirements
• What are Functional Requirements?
• Example of Functional Requirements
• What are Non Functional Requirements?
• Example of Non Functional Requirements
• Key Differences Between Functional and Non Functional Requirements
• Conclusion

Difference Between Functional and Non Functional Requirements

For a better understanding, let’s go through the difference between functional and non functional requirements in a tabular format:

What are Functional Requirements?

Functional requirements are specifications that describe the specific actions or behaviours that a software must be capable of performing. They define what a system should do and frequently describe the inputs, outputs, and processes involved in achieving a specific goal.

To explain functional requiremnets in a layman’s term, we can say that functional requirements, are a set of instructions that describe how a system should work and what it should be capable of.

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Example of Functional Requirements

In order to understand functional requirements in a better way, let’s go through some of the examples. Here are a few examples of functional requirements:

• Users must be able to create an account and log in using a unique username and password. (Online platform)
• The system must allow employees to enter their work hours and submit them for approval. (Time management system)
• Patients should be able to schedule appointments and view their medical history through the system. (Healthcare application)
• Drivers should  be able to enter their route and view real-time traffic updates (Navigation application)

After reading the above examples, you must have noticed , that the requirements stated above describe specific actions or behaviours that the system should be able to perform. They specify what the system should do and frequently include input, output, and processes.

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What are Non Functional Requirements?

Non functional requirements are specifications that describe a software’s quality attributes, such as performance, security, and usability. In short, these types of requirements describe how well a software do something.

To explain non functional requiremnets in a layman’s term, we can say that non functional requirements are characteristics of a software that specify how the system should function, designed, and interact with other systems. 

Example of Non Functional Requirements

In order to understand non functional requirements in a better way, let’s go through some of the examples. Here are a few examples of non functional requirements:

• For 95% of requests, the system must respond in less than 2 seconds (Performance)
• The system must be operational 99.9% of the time. (Availability)
• At least 256-bit encryption must be used to protect user data. (Security)
• At least 10,000 concurrent users should be supported by the system.(Scalability)

After reading the above examples, you must have noticed , that the requirements stated above describe system quality attributes such as performance, availability, security, and saclability. They impose constraints on the system’s design and implementation but are not tied to specific functions or behaviours.

Key Differences Between Functional and Non Functional Requirements 

Here are the key differences between functional and non functional requirements:

• Defining functional requirements is easy, but defining non functional requirements is difficult.
• It is mandatory to meet functional requirements, whereas meeting non functional requirements is not necessary.
• Functional requirements define a software or its component, whereas non functional requirements define the performance attribute of software.
• Functional requirements provide answers to questions, such as what the software should do. On the other hand, non functional requirements provide answers to questions, such as how the software should fulfill the functional requirements.

Conclusion

Functional and non functional requirements are two main types of requirements that describe the functionality and performance of the software. And the main difference between functional and non functional requirements is that functional requirements describe what the system should do. On the other hand, non functional requirements describe how the system should perform.