Functional Vs Non-Functional Requirements: Main Differences

Functional vs non-Functional requirements: Main differences

by Tatsiana Isakova — 3 years ago in Mobile Apps 8 min. read

Description: A clear and fully-detailed functional and non-functional requirements description decreases development time, the project cost, and eliminates miscommunication between the team and stakeholders. Read the article to learn more.

Let’s say you’ve started building a house. In your mind, it is a three-storey house with brown doors and several bathrooms. But that’s not enough. You need to decide on a number of other features. Should it be a modern style?

Will the walls be painted blue? How many windows do you need? Only after pinpointing all the details and nuances, you’ll get the house of your dreams.

This strategy also goes for mobile app building. Point-by-point planning of the project allows business examiners and project managers to make better item documentation.

If the group needs to explain data at the advancement stage, improvement time and expenses may increment, just as the likelihood that the task may fall flat.

How can you dodge this?

Essentially, functional and non-functional requirements set the foundation for successful software development. If done wrong, product requirements distort the final result.

On the one hand, functional requirements are no rocket science. On the other hand, some of the non-functional requirements need some extra effort to outline.

For example,

How can you assess that the performance is decent?


Are there any ways to outline maintainability before any lines of code have been created?

If you want to save some money, boost team performance, and create a profitable and booming project, keep on reading.

This article will unveil the essence of functional and non-functional requirement examples and some advice on how to outline non-functional requirements.
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Are requirements important for the software development process?

Meticulously defined requirements are the way to extend achievement. They also allow the development group and customers to guarantee they are attempting to arrive at similar objectives.

Neglecting to outline requirements may cause misunderstanding between the group and customer, and increment the odds of the venture break-down.

Let’s have a look at some relevant statistics:

  • More than  60% of projects with productive communication and accurate requirements have a larger possibility to release project scope and comply with the rules.
  • Additionally, more than 30% of projects flopped because of inadequate assessment during the planning stage and hazy requirements.
  • At the same time, vague requirements result in dragging out the deadline and increasing the costs to 60%.
  • On top of that, hazy requirements eat up more than 40% of the development cost for programming, staff, and outer expert administrations.

Defined functional and nonfunctional requirements in software engineering help the team to handle the following duties:

Assign the conditions and responsibilities. Requirements will guarantee that the dev team and parties involved are on the same wavelength to stay away from possible confusion later on.

Cut the discussion time. Clear communication with business analyst provides more distinct requirements and cuts the development time. By specifying the requirements, you save precious time and cut the project’s costs.

Make the task assessment more exact. Definite requirements allow us to assess the development time and funding more precisely.

Foresee the potential pitfalls. If the visualization is appropriately done at the inception stage, the team can outline the possible defects beforehand. Thus, you save your time and money.

Make projects more foreseeable. Top-notch requirements call for a tangible prediction process and ensure the project will come out as planned.

To sum it up, detailed requirements help devs and parties involved to find common ground, make a cost-saving project, and meet or exceed the client’s expectations.

Now let us dive into the project requirements types.

Types of requirements

If you want your product idea to work, you have to clear up the following requirements:

Business requirements detail the solution for a project, including the documentation of the client’s goals, needs, and expectations.

Stakeholder or user requirements describe the needs of what users do with the system.

Solution requirements specify the conditions and capabilities needed to meet the goals and expectations, including

Functional requirements describe a list of functions that the system must accomplish.

Nonfunctional requirements mostly define the overall attributes of the resulting system.

Functional vs non-Functional requirements: Main differences 1
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Functional requirements

A functional requirement is a function of the system with inputs required for a system to function and outputs that it produces. The inputs are then added by web & app developers.  These requirements should be meticulously defined both for the dev team and parties involved.

Here are examples of software functional requirements:

  • Business Rules
  • Transaction corrections,
  • Administrative capacities
  • Authentication
  • Authorization levels
  • Audit Tracking
  • External Interfaces

If your team preaches on an Agile approach, they can shape this documentation on paper. However, you may need some visuals to specify the details further.

The possible types of functional requirement docs include:

Functional requirements specification document

It collects all the primary features of the application. The specification document sets out the functions of the system or component needed to perform. The documentation includes detailed descriptions of the product’s functions, appearance, and capabilities.

The specification document must cover the following aspects:

Aim. This part entails context, definitions, and system outline.

General description. This doc includes project vision, business regulation, and suppositions.

Specified requirements. They may include database guidelines, system attributes, and functional requirements.

Here is a project definition example:

“Betterways – a website that will develop course maps for all certificates and degrees with the aim of helping students take the courses they need. It will also offer a map of all viable degrees for all viable certificates”.

Use cases

Use cases capture a set of interaction sequences that a system performs to prepare a result of measurable or visible value to one or more actors. They describe user goals, the user’s view of the system, and a set of task-related activities.

Any use case consists of three primary components:

  • Actors are the users who will interact with the product.


“Student- a person who wants to check the course viability and looks for a course map.”

  • System functional requirements refer to the expected reaction of the product.


“A map searching system finds the course map.”

  • Goals capture all communication between the users and the system.

User stories

User stories are a short description of a little piece of business functionality that usually takes a couple of days to complete. They help deconstruct specific product features into more manageable parts.


“As a Student, I want to find the course map so I can assess its viability.”

The statement clearly outlines the user, their desire, and their intention. In Agile software development, user stories provide context beforehand and help dev teams think more critically.

Functional decomposition

A functional decomposition or work breakdown structure (WBS) demonstrates how complicated processes and features can be divided into more uncomplicated parts. By implementing the work breakdown structure, the team can evaluate each component of the project while catching the whole picture.


Functional vs non-Functional requirements: Main differences 2

Mobile app prototypes

Prototypes help stakeholders and developers specify the project approach and clarify the entangled territories of features being developed.

The dev group additionally utilizes prototypes to demonstrate the functionality of the solution and give examples of how users will use it.

There are two sorts of prototypes:

  • Throwaway ones that can be modest and quick visual portrayals of requirements.


  • Evolutionary prototypes that can be transformed in the early versions of the product or the MVP.

Functional vs non-Functional requirements: Main differences 3

Non-functional requirements examples

What is a non-functional requirement?

Non-functional requirements are essential aspects to consider since they all speak about the properties your product must have. So they help to describe the experience the user has while developing the product.

Here is the list of basic non-functional requirements:


Usability specifies the ease of how well a user in a specific context can use a product to meet the goal effectively.

Legal or Regulatory Requirements

These requirements include all applicable laws, rules, regulations of any Regulatory Authority. If your product does not abide by these regulations, it may result in huge fines.


It demonstrates the probability of failure-free solution for an exact stretch of time in a specified environment.


Performance shows how your solution operates when users interact with it in different environments. Bad performance may result in adverse user experience and endangered system safety.

As we stated, some non-functional requirements are not specified and may be overlooked by the group and parties involved due to:

Emotional nature. Various users can see, decipher, and assess non-functional requirements in multiple ways.

Coordinated nature. The objectives of one non-functional requirement may strife with another since they regularly broadly affect frameworks.

Don’t have the foggiest idea what they [NFRs] are. Hazy phrasing, befuddling definitions, and the nonappearance of a unified plan make comprehension of non-functional requirements quite challenging.

Expecting that they are obvious.  During the inception stage, both the client and the group may disregard some non-functional requirements since some of them are difficult to characterize from the point of view of a business approach. This way, they may emerge simply after the project release.

Outlining non-functional requirements

To specify most non-functional requirements, you should:

  • Utilize a specified categorization and divide them into three categories: operation, revision, and transition. In this case, the parties involved and the dev team create a comprehensive language for considering non-functional needs.
  • With a record of pre-determined elicitation questions, the dev team’s performance will likely boost. Also, it will save you many hours when getting ready for elicitation interviews and workshops.
  • Communicate with the development team when outlining the requirements to guarantee that you are on the same wavelength with the dev team.
  • Utilize ‘Invented Wheels’ and reutilize the requirements created for other systems, since they share a lot of similarities as for non-functional requirements.
  • Make automated testing tools work to your benefit. They will assist with assessing your product performance quicker and show more non-functional requirements.
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Comparing Functional Vs. Non-Functional Requirements

If you still have some difficulties outlining  the difference between functional and non-functional requirements,here’s a table:

Criteria FRs NFRs
Requirement It is compulsory It is non-compulsory
Capturing type It is captured in use cases. It is captured as a quality attribute.
Outcome Product feature Product properties
Capturing Simple to capture Difficult to capture
Aim Allows you to validate the functionality. Allows you to validate the performance.
Focal area Centered on user requirement Centered on the user’s anticipation and experience.
Docs Outlines the abilities of the product Outlines how the product functions
Product Information Product Features Product Properties

The Bottom Line

When you define functional and non-functional requirements, you cut the development costs. As the requirements are clearly outlined, nothing holds the dev team from creating a product. However, some people may have difficulties with specifying them. The difference between functional and non-functional  lies in the following aspects:

Functional requirements are simple to specify since they are business-driven and based on the business idea. They describe all the possible product features and demonstrate how users will interact with them.

Non-functional requirements, on the other hand, are experience-driven.  To define such requirements, you should assess the product’s performance and change it into more effective and appropriate. These requirements emerge when the product is utilized regularly.

To sum it up, functional requirements describe a list of functions that the system must accomplish. Non-functional requirements, on the other hand, specify other constraints such as performance expectations to be used. Therefore, FRs answer the what question, while NFRs answer the how question.

To get assistance from BAs, and outline your project requirements, drop us a line.

Tatsiana Isakova

Tatsiana Isakova is a Belarus-based content writer. She authors in-depth industry insights, opinion pieces as well as reviews and blog posts at The App Solutions.

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