What LLD covers vs HLD - Design Approaches Compared

Design: Understanding Low-Level Design (LLD) vs High-Level Design (HLD)

Focus on conceptual differences and coverage of HLD and LLD. Do not cover detailed coding or specific technology implementations.

Functional Requirements

FR1: Explain the purpose of HLD and LLD in system design

FR2: Describe the main components and focus areas of HLD

FR3: Describe the main components and focus areas of LLD

FR4: Highlight differences between HLD and LLD with examples

FR5: Provide clarity on when and why each design level is used

Non-Functional Requirements

NFR1: Use simple language without jargon

NFR2: Keep explanations beginner-friendly

NFR3: Use relatable real-life analogies

NFR4: Avoid overly technical or implementation-specific details

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

System architecture overview

Module/component breakdown

Data flow and control flow

Class diagrams and sequence diagrams

Interface definitions and APIs

Design Patterns

Top-down design approach

Modular design

Separation of concerns

Abstraction layers

Reference Architecture

HLD and LLD Relationship Diagram:

+-------------------+       +-------------------+
|   High-Level      |       |   Low-Level       |
|   Design (HLD)    | ----> |   Design (LLD)    |
+-------------------+       +-------------------+
| - System overview  |       | - Detailed logic  |
| - Major modules    |       | - Class details   |
| - Data flow       |       | - Algorithms      |
| - Interfaces      |       | - Data structures |
+-------------------+       +-------------------+

Components

High-Level Design (HLD)

Conceptual Design

Provides an overview of the system architecture, major components, and their interactions.

Low-Level Design (LLD)

Detailed Design

Focuses on detailed internal logic of components, including classes, methods, and data structures.

Request Flow

1. Start with requirements gathering.

2. Create HLD to outline system modules and their relationships.

3. Use HLD as a blueprint for LLD.

4. Develop LLD to specify detailed design for each module.

5. LLD guides developers during coding and implementation.

Database Schema

Not applicable as this is a conceptual design comparison.

Scaling Discussion

Bottlenecks

Confusion between HLD and LLD roles can cause design gaps.

Skipping LLD may lead to unclear implementation details.

Over-detailing HLD can delay design progress.

Solutions

Clearly define scope and purpose of HLD and LLD in project documentation.

Use HLD for stakeholder communication and LLD for developer guidance.

Maintain balance: keep HLD abstract and LLD detailed but manageable.

Interview Tips

Time: Spend 10 minutes explaining HLD, 15 minutes on LLD, and 5 minutes on differences and examples.

HLD is like a city map showing neighborhoods; LLD is like detailed building blueprints.

HLD focuses on what components exist and how they connect.

LLD focuses on how each component works internally.

Both are essential and complement each other in system design.

Clear communication of design levels helps smooth development.