Software Engineering basics - Functional Requirements in Software Engineering

Functional Requirements in Software Engineering

A functional requirement specifies what the system should do.
It defines the functions, features, and interactions the software must provide to meet user needs.

Definition

  • Functional requirements describe the services, tasks, or functions the system must perform.

  • They answer the question: “What should the system do?”

Examples of Functional Requirements

  • A system shall allow users to register and log in.

  • The software shall generate monthly sales reports.

  • The ATM shall dispense cash when a valid PIN is entered.

  • The website shall allow users to search for products by name or category.

Characteristics of Functional Requirements

  • Clear and specific – no ambiguity.

  • Testable – can be verified through testing.

  • Traceable – linked to business needs.

  • Complete – covers all intended system behaviors.

Difference from Non-Functional Requirements

  • Functional requirements → Describe what the system does. (e.g., "The system shall send a password reset email").

  • Non-functional requirements → Describe how well the system performs. (e.g., "The email shall be delivered within 60 seconds").

In short: Functional requirements define the core behavior and operations of a software system that directly fulfill user needs.