Room type hierarchy in LLD - System Design Exercise

Design: Room Type Hierarchy System

Design focuses on the class and object hierarchy for room types and their attributes. It excludes UI design, database persistence, and network communication.

Functional Requirements

FR1: Define different room types with common and specific attributes

FR2: Support inheritance of properties from parent room types to child room types

FR3: Allow adding new room types without changing existing code

FR4: Enable querying room types and their attributes

FR5: Support multiple levels of hierarchy (e.g., Room -> Bedroom -> Master Bedroom)

Non-Functional Requirements

NFR1: System should handle up to 1000 room types

NFR2: Query response time for room type details should be under 100ms

NFR3: System should be extensible and maintainable

NFR4: Memory usage should be optimized for embedded or low-resource environments

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Base RoomType class or interface

Derived classes for specific room types

Attribute storage and inheritance mechanism

Factory or builder pattern for creating room types

Query interface for retrieving room type details

Design Patterns

Inheritance and polymorphism

Composite pattern for hierarchical structures

Factory pattern for object creation

Decorator pattern for adding attributes dynamically

Reference Architecture

RoomType (Base Class)
  |
  +-- Bedroom (Derived Class)
       |
       +-- MasterBedroom (Derived Class)
       +-- GuestBedroom (Derived Class)
  +-- Kitchen (Derived Class)
  +-- Bathroom (Derived Class)

Components

RoomType Base Class

Object-Oriented Programming (any language)

Defines common attributes and methods for all room types

Derived RoomType Classes

OOP inheritance

Specialize room types with specific attributes and behaviors

Attribute Storage

Class fields or dictionaries

Store attributes with inheritance support

RoomType Factory

Factory design pattern

Create room type instances dynamically

Query Interface

Methods or APIs

Retrieve room type details and attributes

Request Flow

1. Client requests details for a specific room type

2. Query interface calls the RoomType factory to get the instance

3. RoomType instance returns attributes, including inherited ones

4. Client receives complete room type information

Database Schema

Not applicable - design focuses on in-memory class hierarchy and inheritance

Scaling Discussion

Bottlenecks

Large number of room types causing memory overhead

Deep inheritance chains increasing lookup time for attributes

Difficulty in adding new room types without modifying base classes

Solutions

Use attribute dictionaries with caching to reduce repeated lookups

Limit inheritance depth and use composition for shared attributes

Implement a plugin or registration system for adding new room types dynamically

Interview Tips

Time: 10 minutes for requirements and clarifications, 20 minutes for design and explanation, 15 minutes for scaling and Q&A

Explain the importance of inheritance for code reuse and clarity

Discuss trade-offs between inheritance and composition

Show how design supports extensibility and maintainability

Mention performance considerations for attribute lookup

Highlight how the factory pattern helps in dynamic creation