HLD vs LLD distinction - Quick Revision & Key Differences

Recall & Review

beginner

What does HLD stand for in system design?

HLD stands for High-Level Design. It shows the big picture of the system, focusing on architecture and main components.

beginner

What is the main focus of Low-Level Design (LLD)?

LLD focuses on detailed design of individual components, including algorithms, data structures, and interfaces.

beginner

Which design level describes the system modules and their interactions?

High-Level Design (HLD) describes system modules and how they interact with each other.

intermediate

Give an example of what you might find in LLD but not in HLD.

In LLD, you might find detailed class diagrams, method signatures, and database table schemas, which are not shown in HLD.

intermediate

Why is it important to have both HLD and LLD in system design?

HLD helps understand overall system structure and flow, while LLD provides detailed guidance for developers to implement components correctly.

Which design level focuses on the overall architecture of the system?

A Testing Plan

B Low-Level Design (LLD)

C Code Implementation

D High-Level Design (HLD)

HLD focuses on the overall architecture and main components of the system.

Which of the following is typically part of Low-Level Design?

A System architecture diagram

B Class diagrams and method details

C User interface wireframes

D Project timeline

LLD includes detailed class diagrams and method specifications.

What is NOT a characteristic of High-Level Design?

A Defines system components

B Focus on modules and their interactions

C Detailed database schema

D Shows data flow between modules

Detailed database schema is part of LLD, not HLD.

Who primarily uses Low-Level Design documents?

A Developers

B Project managers

C End users

D Testers only

Developers use LLD to understand detailed implementation.

Which design phase comes first in the system design process?

A High-Level Design

B Low-Level Design

C Coding

D Testing

High-Level Design is created before Low-Level Design.

Explain the key differences between High-Level Design (HLD) and Low-Level Design (LLD).

Think about the big picture versus the detailed parts.

Why do software projects benefit from having both HLD and LLD documents?

Consider different audiences and purposes.

Practice

1. Which of the following best describes the purpose of a High-Level Design (HLD)?

easy

A. It provides detailed code-level logic for each module.

B. It shows the overall system architecture and main components.

C. It lists all the database table schemas.

D. It contains the exact API request and response formats.

Solution

1. Step 1: Understand HLD focus

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

2. Step 2: Compare options

   The option that shows the overall system architecture and main components describes HLD.

3. Final Answer:

   It shows the overall system architecture and main components. -> Option B

4. Quick Check:

   HLD = Big Picture [OK]

Hint: HLD = big picture, LLD = details [OK]

Common Mistakes:

• Confusing HLD with detailed design
• Thinking HLD includes code logic
• Mixing database schema details with HLD

2. Which statement correctly differentiates Low-Level Design (LLD) from High-Level Design (HLD)?

easy

A. LLD is used for planning; HLD is used for coding.

B. LLD shows system modules and their interactions; HLD shows code details.

C. LLD explains detailed logic and data structures; HLD shows system components.

D. LLD focuses on user interface design; HLD focuses on database design.

Solution

1. Step 1: Identify LLD and HLD roles

   LLD explains detailed logic and data structures, while HLD shows system components and their relationships.

2. Step 2: Evaluate options

   The option stating 'LLD explains detailed logic and data structures; HLD shows system components.' correctly differentiates them, matching their definitions.

3. Final Answer:

   LLD explains detailed logic and data structures; HLD shows system components. -> Option C

4. Quick Check:

   LLD = Details, HLD = Components [OK]

Hint: LLD = details, HLD = overview [OK]

Common Mistakes:

• Reversing roles of HLD and LLD
• Confusing planning and coding phases
• Mixing UI and database focus incorrectly

3. Given a system design process, which output is expected from the Low-Level Design (LLD) phase?

medium

A. A diagram showing major system components and their interactions.

B. A high-level flowchart of system data flow.

C. A list of user requirements and business goals.

D. Detailed class diagrams and sequence diagrams for modules.

Solution

1. Step 1: Recall LLD deliverables

   LLD includes detailed design artifacts like class diagrams and sequence diagrams showing module internals.

2. Step 2: Match options to LLD

   Detailed class diagrams and sequence diagrams for modules match the detailed diagrams expected in LLD; others describe higher-level or requirement outputs.

3. Final Answer:

   Detailed class diagrams and sequence diagrams for modules. -> Option D

4. Quick Check:

   LLD = Detailed diagrams [OK]

Hint: LLD = detailed diagrams like class and sequence [OK]

Common Mistakes:

• Choosing high-level diagrams for LLD
• Confusing requirements with design outputs
• Selecting flowcharts meant for HLD

4. A team mistakenly uses High-Level Design (HLD) diagrams to write detailed code logic. What is the main issue with this approach?

medium

A. HLD lacks the detailed information needed for coding.

B. HLD contains too much detail, causing confusion.

C. HLD diagrams are only for database design.

D. HLD is only used after coding is complete.

Solution

1. Step 1: Understand HLD purpose

   HLD provides a broad overview, not detailed logic needed for coding.

2. Step 2: Identify problem

   Using HLD for coding misses necessary details, causing incomplete or incorrect code.

3. Final Answer:

   HLD lacks the detailed information needed for coding. -> Option A

4. Quick Check:

   HLD = overview, not detailed code [OK]

Hint: HLD is overview, not detailed code [OK]

Common Mistakes:

• Thinking HLD has too much detail
• Believing HLD is only for database
• Assuming HLD is post-coding

5. You are designing a new online shopping system. Which design phase should you use to decide the main system components and their interactions, and which phase to define the detailed logic of the payment module?

hard

A. Use HLD for main components and LLD for payment module details.

B. Use LLD for main components and HLD for payment module details.

C. Use HLD for both main components and payment module details.

D. Use LLD for both main components and payment module details.

Solution

1. Step 1: Identify phase for main components

   Main system components and their interactions are defined in High-Level Design (HLD).

2. Step 2: Identify phase for detailed module logic

   Detailed logic, like payment module internals, is defined in Low-Level Design (LLD).

3. Final Answer:

   Use HLD for main components and LLD for payment module details. -> Option A

4. Quick Check:

   HLD = components, LLD = details [OK]

Hint: HLD = components, LLD = detailed logic [OK]

Common Mistakes:

• Swapping HLD and LLD roles
• Using one phase for all design
• Ignoring detailed design for modules