Consider the following set of requirements for Addis Ababa international airport and construct structural modeling with class diagram by specifying all possible relationship and multiplicity.

Addis Ababa international airport requires a system to keep track of flight details for customers. For each flight the system needs to store the flight number, destination, departure time, departure gate, airline and flight cost. Some flights are direct flights, i.e. they fly non-stop to the destination and some fly via another airport to their destination. We will call these flights indirect flights. In this case the flight stops at an airport en route to its destination to refuel. In the case of indirect flights information regarding the transit airport must also be stored. The flight cost is calculated to be the cost charged by the airline per customer plus a percentage of this amount (the profit rate). In the case of indirect flights an additional levy must be added to this amount per customer in order to cover refueling levies at the transit airport. Furthermore, on some flights additional passengers can board the plane at the transit airport. The system needs to keep track of whether boarding will take place at the transit airport or not. The system also needs to store details of the aircraft used for a flight. The aircraft make, model and capacity (number of passengers that it can carry), must be stored for each aircraft.