Why Requirements gathering (functional and non-functional) in HLD? - Purpose & Use Cases

The Big Idea

What if you could avoid costly mistakes by simply asking the right questions first?

The Scenario

Imagine building a house without a clear plan. You ask the owner what they want, but only get vague answers. You start building rooms, but later find out the kitchen needs to be bigger and the roof must withstand heavy snow. You have to tear down walls and redo work repeatedly.

The Problem

Without clear requirements, the project drags on. Builders waste time fixing mistakes. Costs rise, and frustration grows. The final house may not fit the owner's needs, causing disappointment and delays.

The Solution

Requirements gathering helps us collect clear, detailed needs before starting. We separate what the system must do (functional) from how well it must do it (non-functional). This clarity guides design and development, reducing costly changes later.

Before vs After

✗ Before

Start building without clear specs
Fix problems as they appear
Repeat fixes

✓ After

Gather detailed needs first
Plan design based on needs
Build with confidence

What It Enables

Clear requirements enable smooth project flow, better design decisions, and a system that truly meets user needs.

Real Life Example

When creating a mobile app, gathering functional requirements defines features like login and messaging, while non-functional requirements ensure fast loading and data security, leading to a reliable and user-friendly app.

Key Takeaways

Clear requirements prevent costly rework.

Functional needs define what the system does.

Non-functional needs define system quality and constraints.