Functional Vs Non-Functional Requirements : Why Are Both Important?

Abiding by the requirements is always necessary to make a product successful. You might have some confusion when it comes to non-functional and functional requirements. Many questions come up during this discussion. Such as in software engineering, how can you distinguish functional from non-functional requirements? What is the significance of this distinction? Besides functional requirements, why are non-functional requirements significant? This article aims at answering all these questions for you. 

Functional Requirements: What Are They?

In simple terms, functional requirements are the specifications of product features or functions. It is what defines how the software must be able to respond to inputs and what it must do. In other words, Functional requirements describe the goals of the software. Failing to meet the requirements will make your software not work. To understand this better thing about the last time you signed up on any website. Did you receive an email confirmation after you registered? So this functional requirement is added and written down in the development stage. The website must send an email notification to verify your registration. 

Business analysts craft the requirements that are present in the document.. You can figure out the needs of the clients. Afterward, you can work it into the specifications that work with software. 

These functional requirements can include the following: 

• administrative functions
• business requirements
• administrative functions
• reporting requirements 
• certification requirements
• authentication  

What are Non-Functional Requirements?

To understand the main difference between the two, let us divide it into two actions. A non-functional requirement specifies how these functions need to take place. On the other hand, functional requirements define the behavior of the system. Let us take the example of email verification. A functional requirement is that you receive an email notification. The method of sending the email notification is a non-functional requirement. 

Non-functional requirements may include: 

• Performance
• Reliability
• Usability 

The main difference between the two requirements is that functional requirements are essential for system working. Thus, the system will still function even without meeting the non-functional requirement. The system won’t work if it doesn’t meet the functional requirements. 

You cannot undervalue the importance of non-functional requirements, which is a fact.  Functional requirements primarily focus on the client’s needs. The non-functional requirements are more focused on the user. For example, if the client needs website loading, which is a functional requirement. If it takes more than 30 secs to load, then it fails the purpose of the user.

Difference between Functional Vs. Non-Functional Requirements: Why Are They Important?

Many of them wonder if non-functional requirements and functional requirements are vital. All right, then do we have to distinguish between the both of them? No, to a certain extent. Development teams do not differentiate between these two things in practice. Instead, they execute the product’s features to the best of their ability. 

Despite this, it is crucial to differentiate between functional and non-functional approaches. Whenever a client starts a project, he has specific requirements and goals in mind. Work scope should include both needs and wants of the client. And here is where it helps to understand the differences. 

Based on the budget and cost review, the client can change or replace some requirements. In general, only non-functional requirements continue to change.

How Do Requirements Get Written?

Now that we understand what are functional requirements and non-functional requirements. Let’s move into details of how to write these requirements. Both these requirements don’t just come out of nowhere. They have been carefully documented and are present in a variety of forms. The documents may include user stories, specification documents, use cases. We shall look at each one in more detail: 

SRS Document- Software Requirements Specification

In most cases, software requirements come in the form of a specification document. SRS defines product functions and the methods used to accomplish those functions. SRS is a list of all the features a product possesses. 

The SRS document communicates the client’s expectations and needs to the development team. You must consider even the tiniest details of the product. The SRS plays a vital role in estimating the final costs and time required for the development. 

SRS documents typically contain the following sections: 

• Introduction: describes the purpose, terms (document conventions), and provides references. Materials and literature that provide facts and grounding of specific technology theory.
• Overall Description: Include product features (detailed description of each function), design. It also includes implementation constraints, code standards, data exchanges, and business logic restrictions.  
• The System Features: This defines a description of how each feature should work. 
• External Interface Requirement: It describes how the external environment interacts with the system. 
• Non-Functional Requirements: It includes software quality requirements, performance requirements, and security requirements. 

User Stories

The purpose of user stories is to tell the story of a product as if it was the customer’s own. In a typical user story written as: as a (user role), I want to do (goal) for the reasons I stated (reason). ‍

A user story shifts focus with engaging dialogues rather than simply listing features.  Story cards or sticky notes utilize brainstorming aids during planning developer meetings.

User Cases

In Agile development, use cases are like user stories. Users can interact with the system in many different ways by representing it in use cases. However, user stories are a bit more varied from use cases, despite sounding the same. Use cases are steps or flows that lead to a feature’s end purpose, which is entirely opposed to user stories. 

Now, you can understand the technical nature of functional and non-functional requirements. But in reality, you can attain success in any product both the requirements are to co-exist as a single unit.