Differentiating Functional and Non-Functional Requirements

Functional vs Non-Functional Requirements

Identifying the functional vs non-functional requirements is one of the first steps in the software development process. Why are these requirements vital in delivering the best product? Read on to learn more.

The goal of every software development team is to deliver a high-quality product. To achieve this, the team, led by a project manager,  must communicate with the client about what they want. Meaning, both the client and the team must discuss and differentiate between functional vs non-functional requirements for the project.

Is the difference between functional vs non-functional requirements critical in the software development process? How can project management ensure that these requirements are accurate? First, you have to know what software requirements are.

What are Software Requirements?

Defining the software requirements is the first step in the software development process. According to a survey, 39% of software projects fail due to poor requirements analysis.

Thus, these requirements are essential to ensure that both the clients and the development team work towards the same goal. So, what are software requirements?

Simply put, software requirements are the characteristics, features, and functions that you want for your software product. Moreover, the requirements are what the users expect the software will do.

Additionally, there are two main categories of software requirements: functional and non-functional requirements.

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Functional vs Non-Functional Requirements

As stated earlier, without a clear definition of the software project requirements, you will miss the project’s scope. As a result, you will be spending more time and resources to correct the errors in later stages. Thus, from the start of the project, you need to identify the correct requirements.

To achieve this, you will have to define what are the functional and non-functional requirements. But, how will you or your project manager accomplish this task? First, you will need to know the differences between functional vs non-functional requirements.

Functional Requirements

In simple terms, these are the requirements that define your software’s system. Hence, functional requirements tell how the system should work or act when receiving inputs. Listed below are some of the common examples of functional requirements:

  • Authentication
  • Authorization Levels
  • Audit Tracking
  • Administrative Functions
  • Business Rules
  • Corrections, Cancellations, and Adjustment of Transactions
  • Certification Requirements
  • External Interfaces
  • Historical Data
  • Reporting Requirements

As these examples show, functional requirements define the “if-then” behaviors of your software. These behaviors include data inputs, business processes, and calculations.

Non-Functional Requirements

As stated, functional requirements specify what the system must do. On the other hand, non-functional requirements describe “how” it should do it. These requirements do not affect the functionality of the system, thus, named non-functional requirements. Consequently, even without meeting the non-functional requirements, the system will still perform its primary functions.

So, if the system still works without meeting the non-functional requirements, why are they still necessary? They are essential because of usability issues. In other words, they are the requirements that affect the user experience. On that note, below are some of the most common non-functional requirements:

  • Capacity
  • Data Integrity
  • Flexibility
  • Maintainability
  • Performance
  • Portability
  • Reliability
  • Reusability
  • Scalability
  • Security

How well you define and execute the non-functional requirements will affect your system’s ease of use.

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The Difference Between Functional vs Non-Functional Requirements?

Both requirements are essential to developing the product that your client wants. Below are the differences between functional vs non-functional requirements:

Requirements

Functional requirements are mandatory as they define how your system works. Meanwhile, non-functional requirements are not mandatory.

Focus

Non-functional requirements focus on what the users expect from your system. Thus, it answers the question, “How should the software system fulfill the functional requirements.” Meanwhile, functional requirements lay out what the system should do.

Objective

Your functional requirements should verify what the functionalities of your software system are. In contrast, non-functional requirements establish the performance of your system.

Documentation

When documenting functional requirements, it should describe what your software does. In comparison, non-functional requirement documentation should explain how the product works.

Testing

Functional requirements testing systems include End to End, API Testing, and Integration. For non-functional requirements, testing includes Stress, Usability, Performance, Security, and the likes.

Benefits of Defining Functional vs Non-Functional Requirements

Both requirements are essential and interconnected. Here are the benefits that you get when you define and differentiate the requirements correctly:

Getting Everyone on the Same Page

Once you define the functional and non-functional requirements, you can explain the project’s scope to all stakeholders. This way, you bring everyone, including the clients, on the same page. Thus, ensuring that all stakeholders will be working towards the same goal.

Streamlines the Process

When all stakeholders are on the same page, you can minimize irrelevant processes. This is because everyone possesses the same expectations. Thus, by defining the requirements clearly, the team can work more efficiently.

Budget Precision

Because you defined all the requirements, you will have an understanding of the scope of work. Knowing what you need to complete the project, you can have a precise estimate of how much your budget should be.

Bug-Free Application

Alterations of functionalities at the later stages of the development process lead to errors in the software. However, if you identified the requirements in the early stages, your software can be bug-free.

Why Differentiate Functional vs Non-Functional Requirements?

Differentiating what is functional vs non-functional requirements is essential. Developers should not skip this part of the software development process. Remember that the clients specify their wants and needs when building a project. These needs and wants will become the requirements included in your scope.

However, there are times when clients will decide to adjust the scope. For different reasons, clients may want to change, simplify, and replace some of the requirements. Requirements documentation makes it easier to trace which functionalities need adjustments.

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