Suppose a traveler is planning a round trip from San Francisco to Boston and back.
Most likely they’ll contact an airline reservation agent or a travel agent, or perhaps visit an airline's website or a general travel website like Orbitz, providing a query made up of airport and travel time requirements. For the most part these agents are middlemen, and will pass the query off to one of a handful of companies, including ITA Software, that provide search engines for the airlines and the traveling public. Hopefully the search engine will return one or more answers to the query. Each answer consists of a specific set of flights for each part of the trip, and a price. The rest of this talk is about the difficulties search engines face answering such questions.
The search engines run on databases of flights, prices, and seat availability, provided electronically over private networks by the 800 or so airlines of the world. The data is not directly available to the general public and access often must be negotiated with individual airlines. Flight data is updated daily or occasionally more frequently in the case of unexpected cancellations. Prices are updated about ten times a day, and seat availability continuously. A large portion of the flight, price and seat availability data, called published data, is used by all the major search engines, but a significant amount of private data is restricted.