Amazon·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

Jun 2026

Summary

Amazon system design round, object-oriented modeling focus. The whole session was basically one big design question about a restaurant system and they kept drilling into the relationships between entities and how operations like billing and reservations actually flow through the model.

Questions Asked (1)

Design an object-oriented model for a restaurant system. Include entities like Restaurant, Table, Reservation, Menu, MenuItem, Order, OrderItem, Bill, Payment, Customer, and Staff roles such as Waiter, Chef, and Manager. Define the class relationships, key methods, and explain how the design supports reservation booking, order placement, kitchen ticketing, and billing workflows.

System DesignData ModelingTechnical Trade-offs

Author's notes

This one ran the whole interview.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scope, then sketch a high-level class diagram with core entities and relationships, and finally walk through each workflow (reservation, order, kitchen, billing) to validate the design. Emphasize separation of concerns, extensibility, and how the model handles concurrency and state transitions.

Pro tip: Demonstrate maturity by discussing trade-offs (e.g., inheritance vs. composition for staff roles, normalization vs. denormalization for menu items) and how you'd evolve the design for scalability and real-time updates.

1. Clarify Requirements and Scope

Ask questions to understand expected scale, concurrency needs, and whether the system is for a single restaurant or a chain. Confirm which workflows are in scope and any constraints (e.g., real-time kitchen updates).

2. Identify Core Entities and Relationships

List the main classes (Restaurant, Table, Reservation, Menu, MenuItem, Order, OrderItem, Bill, Payment, Customer, Staff with subclasses Waiter, Chef, Manager) and define their associations, aggregations, and compositions.

3. Define Key Methods and Responsibilities

For each class, specify essential methods (e.g., Reservation.book(), Order.addItem(), KitchenTicket.notifyChef(), Bill.calculateTotal()) and ensure single responsibility and proper encapsulation.

4. Walk Through Workflows

Trace each workflow (reservation booking, order placement, kitchen ticketing, billing) using the class interactions, highlighting state changes and method calls. Discuss how the design supports these flows.

5. Discuss Trade-offs and Extensibility

Explain design decisions (e.g., using composition for staff roles, strategy pattern for payment methods) and how the model can be extended for new features (e.g., online orders, loyalty programs).

Key Points to Mention

Use of composition over inheritance for Staff roles to avoid deep hierarchies and allow flexible role assignment.
State management for Table (available, reserved, occupied) and Reservation (booked, cancelled, completed) with appropriate transitions.
Observer pattern for kitchen ticketing: when an Order is placed, notify the kitchen system to create tickets for chefs.
Separation of Bill and Payment: Bill aggregates OrderItems and calculates total; Payment handles different payment methods via strategy pattern.
Concurrency considerations: locking mechanisms for table reservation to prevent double-booking, and thread-safe order updates.
Extensibility: how to add new menu item types (e.g., combos) or staff roles without modifying existing code (open/closed principle).

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.