In this article, we will walk you through the Functional and non-functional requirements, why it is needed, what are the benefits and why it can be useful for your application.

If you are making an application or managing its development, you need to first prepare you end goals, what the application or the website should achieve, what problem it will be solving, otherwise there is high chance that your product may not achieve its end goal, may be poor performing, unrealiable to the clients.

In the software world, we usually have two types of requirement, yeah you guessed it, they are functional and non-functional. let's first see what are functional requirement ?

Functional Requirement

Functional requirement denotes what function you product component must have. Simply put, it defines what you product does. So you can understand if these requirements are not met then you product as a whole fails so it becomes a non-negotiable one. Some examples of Functional requirement are :-

• Use Case :- Use case are diagram which can includes text. These diagram describes user action. All the action combined gives the whole functional requirement of our product. Here is a example of use-case diagram of Airport.
  
  All the user which interact with our system are on the left side and then we have the functionality shown by the help of arrow.
• Written Document Descriptions :- This contains unique names and number - a summary which helps the client and user to understand the system's requirement

Functional requirement are developed by business analyst or system analyst and the product manager makes sure that it is delivered on time.

Non-Functional Requirement

Non-Functional Requirement states how the software do the functional requirement, more simply put, it deals with how the system will do and not what the system will do. It defines the various criteria that are used to evaluate the product like peformance, realiability, maintainability. Let us see some example

• Performance :- This may include things like Effieciency, security, realiability etc
• Design :- The correctness, verifiability and maintainbility.
• Adaptation :- This works with the products flexibility, portability, reusability.
  
  
  The responsibility of Non-Functional Requirement is generally given to developer or software architect and the document by the product manager.

Below are the examples of systems with their functional and non-functional requirement

Example 1: Social Media Platform

Functional requirements:

• Allow users to create an account
• Allow users to post updates and media (such as photos and videos)
• Allow users to like, comment on, and share other users' posts
• Allow users to send direct messages to other users

Non-functional requirements:

• High availability to ensure the platform is accessible at all times
• Security measures to protect user data and prevent unauthorized access
• User interface that is intuitive and easy to navigate
• Moderation tools to address inappropriate or offensive content

Example 2: Flight Booking System

Functional requirements:

• Allow users to search for flights
• Allow users to select flights and book tickets
• Allow users to check in for their flights and receive boarding passes
• Allow airline staff to view and manage bookings

Non-functional requirements:

• Performance and reliability to ensure that the system is available when needed
• Security measures to protect user data and prevent fraudulent activity
• User interface that is easy to use and navigate
• Integration with other systems, such as payment processors and airport databases

I think this will make things clear for you. So we now know both are important in the process of software developement.
Lets summarize the difference between them to make things clear for you.

Functional requirements	Non-functional requirements
It describes what the system should do	It describes how the system should perform
It defines the specific tasks and capabilities that the system should provide	It defines the quality attributes or characteristics that the system should have
Typically expressed as features or functionalities that users can interact with	Typically expressed as performance, usability, security, or other quality criteria that describe the system's behavior
They are directly related to the system's core functionality and purpose	They are indirectly related to the system's core functionality and purpose
Examples: browsing products on an e-commerce website, withdrawing cash from an ATM, creating a social media profile	Examples: fast page load times, secure checkout process, user-friendly interface, high availability, scalability, security, Interoperability

That's all in this article at OpenGenus
Thank you