Hotel, Room, Booking classes in LLD - System Design Exercise

Design: Hotel Booking System

Design focuses on core classes and their relationships for hotel, room, and booking management. Payment processing, user authentication, and UI are out of scope.

Functional Requirements

FR1: Allow creation and management of hotels with multiple rooms

FR2: Support room types and availability tracking

FR3: Enable customers to book rooms for specific dates

FR4: Prevent double booking of the same room for overlapping dates

FR5: Allow cancellation and modification of bookings

Non-Functional Requirements

NFR1: Support up to 10,000 hotels and 100,000 rooms

NFR2: Booking operations should respond within 200ms

NFR3: System availability target is 99.9%

NFR4: Data consistency is important for booking operations

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Hotel class to represent hotel details

Room class to represent individual rooms and their types

Booking class to represent reservations with date ranges

Availability checking logic

Booking management service

Design Patterns

Aggregation between Hotel and Room classes

Composition of Booking with Room and Customer

Use of date range overlap checks

Factory pattern for creating bookings

Observer pattern for availability updates

Reference Architecture

HotelBookingSystem
  |
  +-- Hotel
  |     +-- Room
  |
  +-- Booking
  
Classes:
Hotel -- owns --> Rooms
Booking -- references --> Room
Booking -- has --> date range

Components

Hotel

Class

Represents a hotel with attributes like name, location, and a list of rooms

Room

Class

Represents a room with attributes like room number, type, and status

Booking

Class

Represents a reservation with customer info, room reference, and booking dates

Request Flow

1. User requests to book a room for specific dates

2. System checks the requested hotel's rooms for availability

3. For each room, system checks existing bookings for date overlaps

4. If an available room is found, system creates a Booking instance

5. Booking is saved and room availability is updated

6. Confirmation is sent to the user

Database Schema

Entities: - Hotel(id, name, location) - Room(id, hotel_id, room_number, type, status) - Booking(id, room_id, customer_id, start_date, end_date, status) Relationships: - Hotel 1:N Room - Room 1:N Booking Constraints: - Booking dates must not overlap for the same room

Scaling Discussion

Bottlenecks

Checking room availability for many rooms and bookings can be slow

Booking conflicts due to concurrent requests

Database write contention on booking records

Solutions

Use caching for room availability data with short TTL

Implement optimistic locking or transactions to prevent double booking

Partition booking data by hotel or room to reduce contention

Use asynchronous processing for non-critical updates

Interview Tips

Time: Spend 10 minutes understanding requirements and clarifying assumptions, 20 minutes designing classes and relationships, 10 minutes discussing scaling and trade-offs, 5 minutes summarizing

Explain class responsibilities and relationships clearly

Discuss how to handle booking conflicts and availability checks

Mention data consistency and concurrency control

Highlight scalability considerations and possible optimizations

Show awareness of real-world constraints and trade-offs