HLD vs LLD distinction - Design Approaches Compared

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

Focus on conceptual distinction between HLD and LLD; exclude detailed coding or implementation specifics

Functional Requirements

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

FR2: Describe the main differences between HLD and LLD

FR3: Show examples of components included in HLD and LLD

FR4: Clarify when to use HLD and when to use LLD

Non-Functional Requirements

NFR1: Use simple language without technical jargon

NFR2: Provide clear, relatable examples

NFR3: Keep explanations concise and easy to understand

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

Key Components

System architecture overview

Module breakdown

Data flow diagrams

Class diagrams

Interface definitions

Design Patterns

Top-down design approach

Modular design

Abstraction layers

Reference Architecture

  +---------------------+        +---------------------+
  |   High-Level Design  | -----> |   Low-Level Design   |
  +---------------------+        +---------------------+
          |                                |
          | System overview                | Detailed module design
          | Components and interfaces      | Data structures and algorithms
          | Technology choices             | Code-level details
          v                                v
  +---------------------+        +---------------------+
  |  System Architecture |        |  Detailed Design Docs |
  +---------------------+        +---------------------+

Components

High-Level Design (HLD)

Conceptual diagrams and documents

Provide an overview of the system architecture, main components, and their interactions

Low-Level Design (LLD)

Detailed diagrams and specifications

Describe internal logic, data structures, and detailed module design for implementation

Request Flow

1. Start with requirements gathering

2. Create HLD to outline system structure and major components

3. Review HLD with stakeholders for feedback

4. Develop LLD to specify detailed design of each component

5. Use LLD as a guide for coding and testing

Database Schema

Not applicable as this is a conceptual design distinction

Scaling Discussion

Bottlenecks

Confusion between HLD and LLD can cause design delays

Too much detail in HLD can overwhelm stakeholders

Too little detail in LLD can cause implementation errors

Solutions

Clearly separate HLD and LLD phases with defined goals

Use simple diagrams and summaries in HLD for clarity

Ensure LLD includes all necessary technical details for developers

Interview Tips

Time: Spend 10 minutes explaining HLD, 10 minutes on LLD, and 5 minutes on their relationship and examples

HLD focuses on what the system does and its architecture

LLD focuses on how each part works internally

HLD is for stakeholders and architects; LLD is for developers

Both are essential for successful system design and implementation