Imagine you are preparing a holiday feast. Whatever the occasion, cooking gourmet meals, crafting cozy decor, and preparing garden zones are pretty challenging tasks. What's the menu? How many guests? Photographer?

It's the same story with building apps. Crafting intuitive UI, creating effective business architecture, and providing systems with top-notch functionality is a kind of software development fine art.

Here's where requirements matter. Functional and non-functional, they play a vital role in the software development process. Let's explore the reasons why.

According to Statista, the main reasons why startups did not work out in 2022 were running out of funds (38%), and no market need (35%). Flawed business models and mismatching team skills were named among other pitfalls ⛔️

Most of these issues can be caused by one seemingly indirect thing — poorly written product requirements. Well-thought and properly documented, they are essential to any project.

In the tech world, requirements are generally split into two types: functional and non-functional. They form a clear vision of the future product and serve as a roadmap for the development team. Both of them define desired system behavior, but the different sides of the last.

Let's break down these two.

Functional requirements define actions the product must provide in order to benefit users. Simply put, they describe:

These requirements are determined by the business needs and task analysis. They can be documented and described through the use cases.

To start with simple functional requirements examples, let's look at the... coffee cup.

Software requirements (both functional and non-functional) are crafted by business analysts, in consultation with the development team, including software engineers, solution architects, and other IT specialists.

While functional requirements specification is a kind of guide to the product's underhood and a statement of how it must behave, non-functional requirements (NFR) specify quality attributes designed to improve the product's functionality and user experience.

They are various "itys" , serving as pillars for the solid vault of good user experience. Defining them upfront provides a handy checklist to ensure you don't miss critical requirements for the future product.

If you want to expand your software product along with your business, saying "product must be scalable" is not enough.

You need to be specific, so you might define this point as "develop a system that can manage at least 100,000 users over the next 24 months, so customers don't experience app crashes and errors".

A lack of prioritized non-function requirements can result in vague project scope and a disconnect between the project plan, client expectations, timeframes, and budget.

If functional requirements define the product's key tasks (what does it have to do), non-functional requirements determine the way it should be done (how does it have to do it). Their key difference is that the first ones are vital for the system; without meeting them, your product simply won't work.

Non-functions, in turn, focus on a user experience; the system will work without them. The other thing is that it will lose its meaning — who'd buy a guitar with a bad finish, strings that break too quickly, and no strap button? You can play such an instrument, but Gibson Les Paul will always outperform your product.

So, don't take this in a way that working on non-functional requirements is less significant. Remember that user-centered design rocks: unless the app is user-friendly, your project will not succeed just as well.

Therefore, only the yin-yang combination of functional vs non-functional requirements matters — one cannot exist without the other ☯️