What LLD covers vs HLD - Quick Revision & Key Differences

Recall & Review

beginner

What does HLD stand for and what is its main focus?

HLD stands for High-Level Design. It focuses on the overall system architecture, major components, and their interactions, giving a big picture view without going into details.

beginner

What does LLD stand for and what does it cover?

LLD stands for Low-Level Design. It covers detailed design aspects like class diagrams, data structures, algorithms, and how each component works internally.

beginner

Which design level focuses on component interactions and system modules?

High-Level Design (HLD) focuses on component interactions and system modules, showing how parts fit together.

beginner

Which design level includes class diagrams and method details?

Low-Level Design (LLD) includes class diagrams, method details, and internal logic of components.

intermediate

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

HLD gives a clear overview to understand the system structure, while LLD provides detailed instructions for developers to implement the system correctly.

What is the primary focus of High-Level Design (HLD)?

A Writing code and unit tests

B Detailed class diagrams and algorithms

C Database schema optimization

D Overall system architecture and major components

HLD focuses on the overall system architecture and major components, not detailed implementation.

Low-Level Design (LLD) typically includes which of the following?

A System modules and their interactions

B User interface wireframes

C Class diagrams and method details

D Project timelines and milestones

LLD includes detailed design like class diagrams and method details.

Which design phase helps developers understand how to implement the system?

A High-Level Design

B Low-Level Design

C Requirement Gathering

D Testing

LLD provides detailed instructions for developers to implement the system.

Which design level is more abstract and less detailed?

A High-Level Design

B Unit Testing

C Code Review

D Low-Level Design

HLD is more abstract and focuses on the big picture.

Which of these is NOT typically part of Low-Level Design?

A System architecture overview

B Algorithms

C Data structures

D Class methods

System architecture overview is part of High-Level Design, not LLD.

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

Think about big picture vs detailed instructions.

Why do software projects need both HLD and LLD phases?

Consider the roles of overview and detail in design.

Practice

1. Which of the following best describes what High-Level Design (HLD) focuses on?

easy

A. Database schema and indexing details

B. Detailed class structures and method implementations

C. Writing code for individual modules

D. The overall system architecture and main components

Solution

1. Step 1: Understand HLD purpose

   HLD is about the big picture, showing main parts and how they connect.

2. Step 2: Compare options

   Only The overall system architecture and main components describes overall architecture and main components, which matches HLD.

3. Final Answer:

   The overall system architecture and main components -> Option D

4. Quick Check:

   HLD = overall system view [OK]

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

Common Mistakes:

• Confusing HLD with detailed coding
• Thinking HLD includes method-level details
• Mixing database design with HLD focus

2. Which of these is typically included in Low-Level Design (LLD)?

easy

A. System component interactions

B. User interface wireframes

C. Class diagrams with methods and attributes

D. Network topology diagrams

Solution

1. Step 1: Identify LLD details

   LLD focuses on detailed design like classes, methods, and data structures.

2. Step 2: Match options to LLD

   Class diagrams with methods and attributes describes class diagrams with methods and attributes, which fits LLD.

3. Final Answer:

   Class diagrams with methods and attributes -> Option C

4. Quick Check:

   LLD = detailed class design [OK]

Hint: LLD = classes and methods details [OK]

Common Mistakes:

• Choosing high-level diagrams for LLD
• Confusing UI design with LLD
• Mixing network diagrams with LLD

3. Given a system design process, which step correctly uses HLD and LLD?

medium

A. Write detailed code first, then create HLD diagrams

B. Create HLD diagrams to plan architecture, then LLD for coding details

C. Skip HLD and directly write LLD documents

D. Use LLD to explain user requirements

Solution

1. Step 1: Understand design flow

   Good practice is to start with HLD for overall planning, then LLD for detailed design.

2. Step 2: Evaluate options

   Create HLD diagrams to plan architecture, then LLD for coding details matches this flow: HLD first, then LLD for coding guidance.

3. Final Answer:

   Create HLD diagrams to plan architecture, then LLD for coding details -> Option B

4. Quick Check:

   Design flow = HLD then LLD [OK]

Hint: Plan big picture first (HLD), then details (LLD) [OK]

Common Mistakes:

• Starting with code before design
• Skipping HLD and losing overview
• Using LLD for user requirements

4. A developer wrote detailed class diagrams but missed showing system modules and their interactions. What design level is missing?

medium

A. High-Level Design (HLD)

B. Low-Level Design (LLD)

C. Both HLD and LLD

D. Neither HLD nor LLD

Solution

1. Step 1: Analyze given design

   Detailed class diagrams are part of LLD, but system modules and interactions belong to HLD.

2. Step 2: Identify missing design level

   Since modules and their interactions are missing, HLD is incomplete.

3. Final Answer:

   High-Level Design (HLD) -> Option A

4. Quick Check:

   Missing modules = missing HLD [OK]

Hint: Modules and interactions belong to HLD [OK]

Common Mistakes:

• Confusing class diagrams with HLD
• Thinking LLD covers system modules
• Assuming both designs are missing

5. You are designing a new feature for a large system. Which approach correctly uses HLD and LLD to ensure scalability and maintainability?

hard

A. Design the system modules and their interactions first, then define classes and methods

B. Focus only on database schema and skip other designs

C. Write code immediately and document design later

D. Start with detailed class design, then create overall system diagrams

Solution

1. Step 1: Understand scalable design approach

   Good design starts with HLD to define modules and interactions, then LLD for detailed classes.

2. Step 2: Evaluate options for best practice

   Design the system modules and their interactions first, then define classes and methods follows this approach, ensuring clear structure and maintainability.

3. Final Answer:

   Design the system modules and their interactions first, then define classes and methods -> Option A

4. Quick Check:

   HLD first, then LLD for scalable design [OK]

Hint: Big picture first, then details for scalable design [OK]

Common Mistakes:

• Starting with code before design
• Ignoring system modules and interactions
• Focusing only on database schema