Non-Functional Requirements: Definition and Tips for Better Requirements Gathering

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Well-defined functional and non-functional requirements are a key step when you plan to create a successful application. Identifying your needs and converting them into clear requirements help development teams better understand your goals, product idea, and expectations. They are the first step for the team to get well-prepared for the whole IT project. 

Let’s look at some statistics. Research shows that more than 30% of IT projects fail because of poorly formulated requirements. Additionally, creating unclear requirements can increase the project timeline and budget by up to 60%, so it’s definitely worth learning how to do it right and increase your chances of success. 

First, you must understand what “non-functional requirements” means and how you should describe them correctly in the project specification. Keep reading!

What Are Non-Functional Requirements? A Definition and Examples

Formulating functional and non-functional app requirements is an essential step if you plan to create a new IT product in cooperation with a software house. Specifying expectations affects the effectiveness of the web development process. In particular, it allows developers to better understand your product goals and vision and get well-prepared for the process.

What does “non-functional requirements” mean? To put it simply, non-functional requirements (sometimes called Quality Attributes) describe how the system performs and its operational capabilities. In other words, they define how the system should work and any functionality limits it should have. The requirements are mostly determined by the application type, target group, budget, your needs, and the project’s goals. 

When you plan to build your application, don’t forget about identifying the functional requirements, too—these are equally important when it comes to gathering your needs. Functional requirements focus on functionalities only, and defining them means describing each functionality step by step. 

Let’s go back to the non-functional requirements for a moment. What are the different types? The scale of choice is very wide, so we’re presenting just a few examples to give you a good idea: 

  • Securability
  • Scalability
  • Usability 
  • Availability
  • Accessibility
  • Capacity

Don’t forget about covering some important information in your specification, like the types of the browser you want to adapt the system to or the implementation method. Read on to get the detail— we will discuss each area separately in the next part of this article.

How Non-Functional Requirements Impact the Software Development Process

As mentioned above, clear requirements play an important role in building your application and affect the entire development process. Gathering all the requirements is important from a business point of view and the software house’s perspective. It will help you start a more predictable project, spot possible mistakes, and choose web app architecture wisely. Additionally, determining an app security strategy at the very beginning will undoubtedly save your time and money. 

Making such a decision in the later stages of the project can be harmful. In some situations, it can be very costly to ensure the safety of the application after you’ve started building it. Deciding on the solution much earlier will minimise the risk of additional costs. 

How to Create a Complex Requirements List for Your Project

If you find it difficult to gather requirements on your own, don’t get discouraged. There is an easy way to do that and identify all desirable features and user scenarios and prioritise the most important ones. Attend an Event Storming workshop that will help you establish both functional and non-functional requirements for your project and save money on development. Although the workshop is mainly focused on functional requirements, it is the first step to discuss non-functional ones too. Learn more about how the workshop is conducted here.

event storming studio software
Event Storming example – Studio Software

Non-Functional Requirements: Real-Life Examples

Below, we’ve listed the areas with specific examples of non-functional requirements that should be described in the IT project specification. The choice of requirements depends on your context and desirable outcomes, so adjust them to suit your situation. 

Let’s have a look at some examples.

Availability / Reliability

Ask yourself a question: When can users use your application? When describing non-functional requirements in terms of accessibility, you should specify whether the application needs to function 24/7/365 or be available for a certain number of years.

Performance

Performance is crucial to building an efficient application that can adequately handle user traffic. Accordingly, it is necessary to specify:

  • The maximum number of users simultaneously using the application
  • Potential users’ location
  • How fast the system operates (the maximum response time to users’ actions)
  • How the application uses hardware resources

Supportability

Specify the type of support that will be required in the event of bugs. For example, it could be provided in-house or externally. Indicate:

  • The way users can report bugs
  • How the application will be monitored
  • The maximum time needed to fix errors (broken down into relevant error types)
  • The best way to test the application

Securability

Ensuring application security is one of the important elements in product development. Set security standards to protect your data and avoid possible external attacks. For example:

  • Identify all possible threats in your industry
  • Choose the desired methods in terms of application security
  • Determine whether additional security practices are required (for example, those related to data storage—GDPR)
  • Adjust the security strategy to the situation and take special care of protecting sensitive data, such as personal information or financial data

Implementation

This area covers all issues regarding how to implement the application. You should indicate, for example:

  • When the application will be implemented
  • The target group type and size and how many users will use your app at different stages of development
  • The types of integration necessary for the implementation
  • Guidelines regarding the desired application architecture or specifically required programming languages or frameworks

How to Properly Describe Non-functional Requirements in the Technical Specification

Knowing exactly what non-functional requirements are and having full knowledge about the product properties, you now need to write everything down in the technical documentation. As we mentioned at the beginning of the article, properly describing the requirements affects the project’s success. If you are wondering what the entire technical specification should look like, check out this article where we comprehensively describe the content of this document.

One of the key rules is to prepare an accurate, clear, and logical description of your requirements. Providing accurate information will help the development team create a successful product that meets your needs. Try to avoid any gaps that make the team uncertain about your product vision. 

What else is worth paying attention to when describing non-functional requirements? The form doesn’t need a specific scheme—a detailed description in bullet points is sufficient. Below, you can find some examples:

  • The application must handle 2,000 users at the same time
  • The application works on web browsers such as Internet Explorer
  • The application will respond to the user’s request within three seconds

Preparing non-functional requirements doesn’t have to be difficult. If you have a clear product idea, writing them down should come easily. However, if you are unsure about the application’s functionality and want to analyse how it works, attend Event Storming workshops to fully understand how your system operates.

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