# Design a Conversational Flight Search, Booking, and Price-Tracking Service Design a service for roughly 30 million daily active users. A user can chat with an agent to search for and schedule a flight, and can follow the lowest price for an itinerary. Queries may be underspecified, such as "I want to visit Europe next year," and valid results can include connecting flights rather than only direct routes. Explain how the conversational layer turns vague intent into a validated search, how itinerary search and booking remain correct, and how price tracking notifies users without overwhelming flight suppliers. ### Constraints & Assumptions - Supplier prices and availability can change between search and booking. - The language model is not a source of truth for schedules, fares, or booking state. - A booking or payment request may be retried. - Exact peak load, supplier quotas, and freshness targets must be elicited rather than assumed. ### Clarifying Questions to Ask - Does "schedule" include purchasing, or only selecting and saving an itinerary? - Which origins, date flexibility, budget, trip length, and destination preferences are known? - What does "lowest price" mean across cabin, baggage, refundability, and connection count? - How quickly must price alerts react, and how often may a user be notified? ### What a Strong Answer Covers - Structured intent extraction plus clarification for missing constraints - A bounded tool interface that grounds the model in authoritative search results - Multi-leg itinerary generation, ranking, repricing, and booking idempotency - Scalable caches, asynchronous price checks, deduplication, and supplier rate limits - Safety, privacy, observability, and graceful degradation ### Follow-up Questions - How do you stop the agent from inventing an airport or fare rule? - How would you search a continent without querying every airport equally? - What happens when the price rises at checkout? - How do you prevent millions of identical price watches from triggering identical supplier calls?