Functional vs Non Functional Requirements for Your Project

The expertise and proficiency of your team, the technology stack, the testing and QA process: lots of factors may make or break a software project. Its success also depends on how good your application іs at solving user problems. One thing, however, is crucial for building a great product: clearly outlining functional and non-functional requirements at the earliest stage of software development. 

The Analysis phase of any software development life cycle starts with defining core business demands, outlining the stakeholder expectations, and gaining insights about how the software will serve the end-users. At this phase the collection and research of the project’s business and technical requirements take place.

In this article, we will explore why accurately defined requirements are important for successful software development. We will also learn to distinguish between functional and non-functional requirements and look at some practical examples. Read on to learn more!

Specs and requirements: Why are they important?

Clear requirements provide developers with comprehensive guidelines, acceptance criteria for the product, and an achievable roadmap they can follow. On top of that, good product specs based on correctly defined requirements translate into a range of tangible benefits:

1. Minimizing iterations and mistakes

With product requirements accurately defined, the developers know precisely what they’re building and can identify and fix bugs at early product development stages. This helps them make fewer mistakes and reduces the number of iterations.

2. Improving time-to-value

Minimizing mistakes helps developers boost productivity and achieve better time-to-value. In the competitive business environment of today, this is a serious advantage.


3. Cutting the development cost

It’s no secret; developers’ hourly rates often defy imagination. With requirements clearly defined, bringing the project to fruition takes less time and consumes less financial resources. If you have a T&M contract, this could be a substantial benefit.

4. Creating a better user experience

Created with the end-user in mind, good product specs help developers include exactly the features and functions that customers are waiting for. With clearly defined requirements you also stand a better chance of offering customers a top-notch user experience.

Read also: How to Create a Mobile App Specification


All in all, good project requirements help build a solution that will bring business value to both customers and stakeholders, and as fast and efficiently as possible. The demands outlined in the product documentation fall into the two main categories: functional and non-functional.

Further, we will examine them in more detail, look at concrete examples, and learn to distinguish between the two requirement types.

What are functional requirements?

Functional requirements refer to what exactly a particular piece of software is supposed to do, and how it is supposed to behave in certain circumstances. More specifically, functional requirements may include:

  • calculations,
  • data manipulation and processing,
  • technical operations,
  • user interactions, and
  • any other application-specific functionality

If you’re having difficulties understanding functional requirements, examples should set you on the right track: 

  • A banking app that automatically transfers a portion of a user’s money to a savings account.
  • A ride service app that notifies drivers about a drive request coming from a specific area.
  • A content management system that creates an automatic preview of a webpage before it is approved and published.
  • A fintech app that carries out an authentication procedure after a user logs in.

As you can see, these examples illustrate some of the very specific functions that software applications provide: communication, transactions, technical services, user authentication, etc. The scope of your functional requirements will ultimately depend on the problems an application aims to resolve and on the business value it is supposed to bring.


To outline the requirements as clearly as possible, the developers and stakeholders try to put themselves into the users’ shoes and empathize with their problems. These findings are further formalized in a specification document (SRC) containing functional and non-functional requirements for your future project.

In addition to the SRC, functional requirements may come in a range of formats like:

  • User stories: user perspective on the desirable app functions
  • Use cases: describing how an application is expected to interact with users
  • WBS, a.k.a. functional decomposition: describing how large app functions are broken into smaller features
  • Prototypes: representations of the system which may further evolve into an MVP
  • Visual representations: diagrams, models, etc.

Read also: Why Should You Choose Rapid App Prototyping Prior to Building Your MVP?


What are non-functional requirements?

Before we move on to non-functional requirements, let’s try to figure out which attributes, besides purely functional ones, does any software system have? As stated above, it’s not only what it does, it’s also how it works.

When it comes to understanding what non-functional requirements are, examples from real-life could give you a great illustration: imagine you have hired two teams to build two very similar houses. Both teams accomplished their tasks but apart from the identical number of floors and bedrooms, the houses are distinctly different.

One looks friendly and inviting, and the other makes you feel cramped even though it’s not too small. One has walls built from solid and durable material and looks like it could withstand a tornado. The other one has frail and brittle walls and feels like it could fall apart any minute. One has doors equipped with smart locks, the other one offers a standard, not so fancy mechanical door lock system, and doesn’t seem secure.

Contrary to functional requirements, non-functional requirements are specific product attributes that create a user experience. For example, a software product may have the following attributes: 

1. Usability

This refers to the user experience and its quality. Is the app easy or difficult to navigate? How long does it take to get to a certain function? Does it have an intuitive interface?

Examples: Upon authentication, a money transfer function should be available in two clicks.

2. Security

This feature ensures that the system is protected from intrusions and that user data is safeguarded from theft or unauthorized manipulations.

Examples: Only a certain category of users may access data on payments and transactions. 


3. Scalability

How well does the system handle increased workloads? The increase in users or in the number of operations could demand an extension of its storage, compute and network capacities or to use data compression techniques.

Example: The website should be able to support 300,000 users simultaneously.

4. Performance

Performance is how well the system responds to user input. This attribute includes latency – the average wait time for a response.

Example: Website page load time should not exceed 1,5 seconds.

5. Availability

This attribute describes how easy users can access the system. Ideally, any application should provide non-disruptive performance – in reality though, downtime occurs due to maintenance work and updates.

Examples: Service downtime shouldn’t exceed 20 minutes. The users should be redirected to a front website page during the downtime period. 

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Functional and nonfunctional requirements: What’s the difference?

Functional vs non-functional requirements are not mutually exclusive: both sets of requirements are crucial for the product’s success. But what is the key difference?

In a nutshell, functional requirements refer to the product’s concrete features  (“what it should do”), whereas non-functional requirements describe the characteristics of an entire system (“how it should do it”). Generally speaking, functional requirements are all about what an application does and focuses on its functionality, while non-functional requirements account for the quality of the user experience.

The tricky part about non-functional requirements is that they are often subjective and therefore difficult to define. It’s easy to omit or overlook them at the early phase of the SDLC. This may happen because the team and the stakeholders haven’t agreed on the specific definitions or have falsely assumed that a certain feature should be integrated by default. However, these omissions may resurface at other development stages, and may seriously impact the product in general. 

Defining functional and non-functional requirements for your project demands accuracy and expertise. Here at Eastern Peak, we approach the product’s inception phase with consideration and professionalism.

Ready to translate your product idea into clear development guidelines? Contact us now for a free consultation!

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