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Requirements Definition: What is it and how to apply it? | Complete Guide

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In order to deliver a successful project, it is essential that the requirements are correctly and accurately defined. Defining requirements can be tricky though – get it wrong and your project will suffer schedule delays, wasted resources, or customer dissatisfaction. In this guide, we’ll look at what the requirements definition is, and how you can apply it in your own projects. Let’s get started!

What are the requirements?

The requirements of a software project are the functions, features, and constraints that need to be met by the final product. In other words, the requirements define what the software should do, how it should look, and any conditions that must be met for it to be considered successful.

Gathering requirements is essential in order to create a product that meets the needs of the customer or client. It is important to note that requirements can change throughout the course of a project, and so it is important to have a mechanism in place to track and manage these changes.

Types of Requirements:

There are broadly two types of requirements:

  1. System Requirements – System requirements can be called the expanded version of the user requirements. System requirements act as the commencement point for any new system design. These requirements are a detailed description of the user requirements the system must satisfy. 
  1. User Requirements – User requirement is a combination of functional and non-functional requirements. These user requirements must be designed in such a way that they are easily understandable by users who do not have any sort of technical knowledge. Hence, they must be written in natural language using simple tables, forms, and diagrams. Also, make sure the document does not have details on system design, software, or formal notations.

Functional Vs Non-Functional Requirements:

Functional Requirements, as the name suggests, describe the functions of the system to be designed. It is a description of what the system will be and how it will function to satisfy user needs. They provide a clear description of how the system is supposed to respond to a particular command, the features, and what the users expect. 

Non-Functional Requirements explain the limitations and constraints of the system to be designed. These requirements do not have any impact on the functionality of the application. Furthermore, there is a common practice of sub-classifying the non-functional requirements into various categories like:

  • User Interface
  • Reliability 
  • Security
  • Performance
  • Maintenance
  • Standards 

Sub-classifying the non-functional requirements is a good practice. It helps when creating a checklist of the requirements that are to be met in the system to be designed. 

Non-functional requirements are as important as functional requirements are. If functional requirements specify what a system should do, non-functional requirements describe how the system will do it. For example, the new application shall provide us with the final list of all connected users. That is a part of functional requirements. If the requirement says that the system would only work on a Windows and a Linux system, that would be a part of non-functional requirements. 

The only difference between the two is that the system can not function without satisfying all the functional requirements. On the other hand, the system will give you the desired outcome even when it does not satisfy the non-functional requirements. 

Defining Requirements:

The most significant aspect of any project is its requirements document. Misconceptions, incorrectitudes, or excesses in the criteria will necessarily result in delays to the schedule, resources lost, and consumer dissatisfaction.

The requirements analysis should start with business or organizational needs and turn them into project needs. If meeting stated standards would be excessively expensive or take an inordinate amount of time, the project’s requirements may have to be compromised, downscaled, or reduced in negotiations with clients or sponsors.

How to define requirements?

There are different ways for requirements definition, but all share some common steps:

  1. Identify the stakeholders and their needs
  2. Define the scope of the project
  3. Draft functional and non-functional requirements
  4. Prioritize the requirements
  5. Validate the requirements with stakeholders

Let’s take a closer look at each of these steps.

Identifying the stakeholders and their needs is the first step in the requirements definition process. Stakeholders are individuals or groups who have a vested interest in the project. They can be internal (e.g., employees of the company) or external (e.g., customers, suppliers, regulators). It is important to identify all stakeholders and their needs early on in the project, as their input will be crucial in defining the requirements.

The second step is to define the scope of the project. The scope defines the boundaries of the project and includes everything that will be delivered as part of it. Defining the scope early on helps to prevent scope creep, which is when additional features or functionality are added to the project beyond what was originally agreed.

The third step is to draft functional and non-functional requirements. Functional requirements are those that describe what the software should do, such as ‘The software should be able to login users’. Non-functional requirements are those that describe how the software should work, such as ‘The software should be responsive’. It is important to draft both types of requirements, as they both serve different purposes.

The fourth step is to prioritize the requirements. This helps to ensure that the most important requirements are addressed first in case there are limited resources or time. Requirements can be prioritized using various methods, such as MoSCoW (must have, should have, could have, would have) or Kano (must have, delight have).

The fifth and final step is to validate the requirements with stakeholders. This helps to ensure that the requirements accurately reflect the needs of the stakeholders. Validation can be done through various methods, such as interviews, focus groups, or surveys.


Defining requirements is a crucial step in any project. By following the steps outlined above, you can ensure that all stakeholders have their needs met and that the project stays on track. By understanding what your requirements are, you can ensure that you get the right software for your needs. The 5-step procedure we outlined should help you gather the information you need to make an informed decision about which software is right for you.

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