Functional Requirements Engineering vs. Non-Functional Requirements Engineering

Attribute	Functional Requirements Engineering	Non-Functional Requirements Engineering
Definition	Specifies what the system should do	Specifies how the system should perform
Focus	Functionality of the system	Performance, usability, security, etc.
Measurability	Can be objectively verified	Can be subjective and difficult to measure
Dependencies	Dependent on business requirements	Dependent on functional requirements

Introduction

Functional and non-functional requirements are essential components of software development. Functional requirements define what a system should do, while non-functional requirements specify how the system should perform. Both types of requirements play a crucial role in ensuring the success of a software project.

Functional Requirements Engineering

Functional requirements are the specific actions that a system must be able to perform. These requirements are typically described in terms of inputs, outputs, and processes. Functional requirements are often considered the "what" of a system, outlining the features and functionalities that the software must have to meet the needs of its users.

Functional requirements are usually documented in a Functional Requirements Specification (FRS) document. This document serves as a blueprint for the development team, providing clear guidelines on what needs to be implemented. Functional requirements are typically prioritized based on their importance to the overall system functionality.

One of the key advantages of functional requirements engineering is that it provides a clear roadmap for development. By defining the specific features and functionalities that the software must have, functional requirements help ensure that the final product meets the needs of its users. Additionally, functional requirements serve as a basis for testing, allowing the development team to verify that the system behaves as expected.

However, one limitation of functional requirements engineering is that it can sometimes be too focused on the "what" of the system, neglecting important aspects of how the system should perform. This is where non-functional requirements engineering comes into play.

Non-Functional Requirements Engineering

Non-functional requirements define the quality attributes of a system, such as performance, reliability, security, and usability. These requirements specify how the system should perform, rather than what it should do. Non-functional requirements are often referred to as the "ilities" of a system, as they describe the system's characteristics.

Non-functional requirements are typically documented in a Non-Functional Requirements Specification (NFRS) document. This document outlines the performance, security, and usability requirements that the system must meet. Non-functional requirements are often more subjective than functional requirements, as they are focused on the user experience and system performance.

One of the key advantages of non-functional requirements engineering is that it ensures the overall quality of the system. By specifying performance, security, and usability requirements, non-functional requirements help ensure that the system meets the needs of its users in terms of reliability and performance. Additionally, non-functional requirements help set expectations for stakeholders regarding the system's performance.

However, one limitation of non-functional requirements engineering is that it can sometimes be challenging to quantify and test. Unlike functional requirements, which can be easily verified through testing, non-functional requirements are often more subjective and difficult to measure. This can make it challenging for development teams to ensure that the system meets all non-functional requirements.

Comparison

Functional and non-functional requirements engineering both play crucial roles in software development, but they focus on different aspects of the system. Functional requirements define what the system should do, while non-functional requirements specify how the system should perform. Both types of requirements are essential for ensuring the success of a software project.

• Functional requirements focus on the features and functionalities of the system, outlining specific actions that the system must be able to perform.
• Non-functional requirements focus on the quality attributes of the system, specifying performance, security, and usability requirements.
• Functional requirements are typically documented in a Functional Requirements Specification (FRS) document, while non-functional requirements are documented in a Non-Functional Requirements Specification (NFRS) document.
• Functional requirements provide a clear roadmap for development and testing, ensuring that the system meets the needs of its users.
• Non-functional requirements help ensure the overall quality of the system, setting expectations for stakeholders regarding performance and reliability.

In conclusion, both functional and non-functional requirements engineering are essential components of software development. While functional requirements focus on the features and functionalities of the system, non-functional requirements specify the quality attributes that the system must meet. By considering both types of requirements, development teams can ensure that the final product meets the needs of its users in terms of functionality and performance.