Airfares are typically made up of fare and rule components that define the airfare product, services and price and includes: origin/destination pair, fare class, one-way/round-trip indicator, fare amount, validity dates, mileage and other rules.[1] To sell the airfares many airlines rely on inventory allocations within finite, alphabetically-defined sub-groups – “inventory buckets” – and fare codes for each fare sold. Airlines have sold airfares in this way since the beginning of commercial air travel and before computer reservations system's existed. As new computerized systems were gradually introduced to the air transport industry in the 1960s this method of defining airfares and managing them within fare codes was further developed and usage became widespread.