HLD vs LLD distinction - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Difference in abstraction levels between HLD and LLD

Which statement best describes the difference in abstraction between High-Level Design (HLD) and Low-Level Design (LLD)?

A HLD and LLD are identical and used interchangeably in system design.

B HLD describes database schemas and code syntax, while LLD only shows user interface layouts.

C HLD is concerned with writing code, while LLD is about deployment and infrastructure setup.

D HLD focuses on system architecture and components, while LLD details the internal logic and algorithms of each component.

💡 Hint

Think about which design level shows the big picture and which one shows the detailed steps.

HLD provides a broad overview of the system architecture and major components. LLD breaks down these components into detailed logic, algorithms, and data structures.

❓ Architecture

intermediate

Identifying HLD and LLD elements in a design document

Given a design document, which element belongs to Low-Level Design (LLD) rather than High-Level Design (HLD)?

A System component interaction diagrams

B Class diagrams showing methods and attributes

C Overall system architecture block diagram

D Deployment environment overview

💡 Hint

LLD focuses on detailed design inside components, such as classes and methods.

Class diagrams with methods and attributes are detailed and part of LLD. System interaction and architecture diagrams are part of HLD.

❓ scaling

advanced

Scaling considerations in HLD vs LLD

When designing a large-scale system, which design level primarily addresses how to scale components and manage system capacity?

A High-Level Design, because it defines system components and their interactions for scalability.

B Low-Level Design, because it details the code optimizations for scaling.

C Neither HLD nor LLD focus on scaling; it is handled only during deployment.

D Both HLD and LLD equally focus on scaling at the same level of detail.

💡 Hint

Consider which design level deals with system-wide structure and capacity planning.

HLD addresses scaling by defining components, their interactions, and system capacity. LLD focuses on internal component details, not overall scaling.

❓ tradeoff

advanced

Tradeoff in detail level between HLD and LLD

What is a key tradeoff when deciding how much detail to include in High-Level Design versus Low-Level Design?

A HLD and LLD should always have the same level of detail to avoid miscommunication.

B More detail in HLD speeds up coding; more detail in LLD slows down testing.

C More detail in HLD can cause confusion; too little detail in LLD can cause implementation errors.

D Less detail in HLD means no need for LLD; more detail in LLD means no need for HLD.

💡 Hint

Think about clarity for different audiences and stages of development.

HLD should be clear and not too detailed to avoid confusion among stakeholders. LLD needs enough detail to guide developers and avoid errors.

❓ estimation

expert

Estimating time allocation for HLD and LLD phases

A project manager wants to allocate design time between High-Level Design and Low-Level Design for a complex system. Which estimation is most reasonable?

A Spend about 30% of design time on HLD and 70% on LLD, because detailed coding plans take longer.

B Spend equal time (50%-50%) on HLD and LLD, as both are equally important and complex.

C Spend about 70% of design time on HLD and 30% on LLD, because system architecture is more complex.

D Spend 90% on HLD and 10% on LLD, since LLD is just minor details.

💡 Hint

Consider which design phase requires more detailed work and documentation.

LLD involves detailed design of components, algorithms, and data structures, which usually takes more time than the broader HLD phase.

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