The University of SydneyPage 9ticket (purchase)baggage (check)gates (load)runway (takeoff)airplane routingdepartureairportarrivalairportintermediate air-trafficcontrol centersairplane routingairplane routingticket (complain)baggage (claimgates (unload)runway (land)airplane routing
ticketbaggagegatetakeoff/landingairplane routingLayering of airline functionality
layers:each layer implements a service§via its own internal-layer actions§relying on services provided by layer below