Why What high level design encompasses in HLD? - Purpose & Use Cases

The Big Idea

What if you could avoid costly mistakes by planning your system before building a single line of code?

The Scenario

Imagine building a complex machine without a clear plan. You start assembling parts randomly, hoping they fit together. As the machine grows, you realize some parts clash, others are missing, and fixing one issue breaks another.

The Problem

Working without a high level design is slow and confusing. You waste time fixing unexpected problems. The system becomes fragile and hard to understand. Team members get lost, making mistakes and repeating work.

The Solution

High level design gives you a clear blueprint before building. It shows the main parts, how they connect, and their roles. This plan guides the team, avoids clashes, and makes the system easier to build and maintain.

Before vs After

✗ Before

Start coding modules without plan
Fix bugs as they appear
Struggle to integrate parts

✓ After

Create architecture diagram
Define modules and interfaces
Build modules following design

What It Enables

With high level design, you build complex systems confidently and efficiently, reducing errors and saving time.

Real Life Example

Before constructing a house, architects create blueprints showing rooms, plumbing, and wiring. Builders follow these plans to avoid costly mistakes and ensure everything fits perfectly.

Key Takeaways

High level design provides a clear system blueprint.

It helps teams coordinate and avoid integration issues.

It saves time by preventing costly errors during development.

Practice

1. What does a high level design (HLD) primarily show in a system?

easy

A. The user interface colors and fonts

B. The main components and how they connect

C. The detailed database schema

D. The exact code for each module

Solution

1. Step 1: Understand the purpose of HLD

   HLD focuses on the big picture, showing main parts and their relationships.

2. Step 2: Differentiate from detailed design

   Detailed code or UI specifics are not part of HLD but come later in design phases.

3. Final Answer:

   The main components and how they connect -> Option B

4. Quick Check:

   HLD = Big parts and connections [OK]

Hint: HLD = big parts + connections, not code or UI [OK]

Common Mistakes:

• Confusing HLD with detailed design
• Thinking HLD includes UI styling
• Assuming HLD shows exact code

2. Which of the following is a correct element to include in a high level design document?

easy

A. Component diagrams showing system parts

B. Detailed API code snippets

C. Exact SQL queries for database

D. Pixel-perfect UI mockups

Solution

1. Step 1: Identify typical HLD contents

   HLD includes diagrams of components and their interactions, not code or UI details.

2. Step 2: Eliminate incorrect options

   Code snippets, SQL queries, and UI mockups belong to detailed design or implementation.

3. Final Answer:

   Component diagrams showing system parts -> Option A

4. Quick Check:

   HLD = component diagrams [OK]

Hint: HLD shows diagrams, not code or UI details [OK]

Common Mistakes:

• Including code snippets in HLD
• Confusing HLD with low-level design
• Adding UI mockups in HLD

3. Given a high level design showing components A, B, and C connected in sequence, what is the most likely data flow?

medium

A. Data flows from A to B to C

B. Data flows from C to B to A

C. Data flows randomly between components

D. No data flows between components

Solution

1. Step 1: Analyze component connections

   Sequence connection means data moves in order from first to last component.

2. Step 2: Determine flow direction

   Data flows from A to B to C as per the sequence shown.

3. Final Answer:

   Data flows from A to B to C -> Option A

4. Quick Check:

   Sequence = A -> B -> C data flow [OK]

Hint: Follow arrows in sequence for data flow direction [OK]

Common Mistakes:

• Reversing data flow direction
• Assuming random data flow
• Ignoring component connections

4. A high level design diagram shows a database connected directly to the user interface without any backend service. What is the main issue here?

medium

A. Database should connect only to frontend

B. Too many components included

C. Missing backend layer to handle business logic

D. User interface should connect directly to database

Solution

1. Step 1: Identify missing architectural layer

   Backend services handle logic and security between UI and database.

2. Step 2: Understand why direct UI to database is bad

   Direct connection risks security and breaks separation of concerns.

3. Final Answer:

   Missing backend layer to handle business logic -> Option C

4. Quick Check:

   Backend needed between UI and database [OK]

Hint: UI never connects directly to database [OK]

Common Mistakes:

• Thinking UI can safely connect to database
• Ignoring backend role
• Confusing component count with design quality

5. When creating a high level design for a scalable web application, which of the following should be included?

hard

A. Detailed SQL queries for data retrieval

B. Exact CSS styles for responsive design

C. User passwords and encryption keys

D. Components like load balancers, web servers, and databases with their interactions

Solution

1. Step 1: Identify scalable system components

   Load balancers, web servers, and databases are key parts for scalability.

2. Step 2: Exclude irrelevant details

   CSS styles, SQL queries, and sensitive data are not part of HLD.

3. Final Answer:

   Components like load balancers, web servers, and databases with their interactions -> Option D

4. Quick Check:

   HLD = scalable components + interactions [OK]

Hint: Include scalable components, exclude code and secrets [OK]

Common Mistakes:

• Adding UI styles in HLD
• Including sensitive data in design
• Confusing HLD with implementation details