Difference Between Functional and Non Functional Requirements

Difference Between Functional and Non Functional Requirements

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Anshuman
Anshuman Singh
Senior Executive - Content
Updated on Jan 10, 2023 18:30 IST

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.

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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

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

Benchmark Functional Requirements Non Functional Requirements
Defines The core functionality of the software. How is that functionality delivered.
Captured in Use case Quality attribute
Is it mandatory to meet these requirements? Yes No
Helps in verifying the Functionality of the software. Performance of the software.
Types of testing to check for these requirements are API, System, End to End, Integration testing, etc. Stress, Performance, Usability, Security testing, etc.
It gives answers to questions, such as What should the software do? How should the software fulfill the functional requirements?
Defining these requirements is Easy Difficult
Example Customers should be able to look for items by entering keywords into the software. The software should support at least 100 concurrent users.

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.

FAQs

What are functional requirements, and how do they differ from non-functional requirements?

Functional requirements specify what a system should do, outlining its core features and functionalities. Non-functional requirements, on the other hand, define how the system should perform in terms of aspects like speed, security, and usability.

Can you provide examples of functional and non-functional requirements for a software project?

Functional requirements might include features like user registration, login, and a shopping cart for an e-commerce website. Non-functional requirements could encompass response time, data security, and accessibility guidelines.

Why are both functional and non-functional requirements important in software development?

Functional requirements ensure that the software meets user needs, while non-functional requirements guarantee that it performs reliably and efficiently. Both types are crucial for delivering a successful and user-friendly product.

How do you prioritize functional and non-functional requirements during the software development process?

Prioritization depends on project goals. In some cases, functional requirements may take precedence, while in others, non-functional requirements, like security or compliance, may be more critical.

What happens if non-functional requirements are not met in a software project?

Failing to meet non-functional requirements can lead to issues such as poor user experience, security vulnerabilities, or system instability. It's essential to address both types of requirements to deliver a high-quality software product.

About the Author
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Anshuman Singh
Senior Executive - Content

Anshuman Singh is an accomplished content writer with over three years of experience specializing in cybersecurity, cloud computing, networking, and software testing. Known for his clear, concise, and informative wr... Read Full Bio