Flight Seat Booking System Design

Design a flight seat booking system - OOD.

Asked in the onsite stage. Treat booking correctness as transactional and authoritative; ML may assist with seat recommendations but must never decide inventory ownership.

Address:

1. Define core classes, interfaces, and booking state transitions.
2. Design seat-map retrieval, seat selection, reservation, payment handoff, confirmation, and cancellation.
3. Explain how an ML retrieval, ranking, and re-ranking layer could recommend seats without violating eligibility or availability constraints.
4. Handle concurrent bookings, retries, expiration, duplicate requests, and partial failures.
5. Discuss testing, observability, data leakage, feature drift, and training-serving skew.

Clarify missing scale, latency, availability, consistency, payment, and compliance requirements before selecting infrastructure.