Consider the AIRLINE relational database schema shown in Figure 5.8, which describes a database for airline flight information. Each FLIGHT is identified by a Flight_number, and consists of one or more FLIGHT_LEGs with Leg_numbers 1, 2, 3, and so on. Each FLIGHT_LEG has scheduled arrival and departure times, airports, and one or more LEG_INSTANCEs— one for each Date on which the flight travels. FAREs are kept for each FLIGHT. For each FLIGHT_LEG instance, SEAT_RESERVATIONs are kept, as are the AIRPLANE used on the leg and the actual arrival and departure times and airports. An AIRPLANE is identified by an Airplane_id and is of a particular AIRPLANE_TYPE. CAN_LAND relates AIRPLANE_TYPEs to the AIRPORTs at which they can land. An AIRPORT is identified by an Airport_code. Consider an update for the AIRLINE database to enter a reservation on a particular flight or flight leg on a given date.

a. Give the operations for this update.
b. What types of constraints would you expect to check?
c. Which of these constraints are key, entity integrity, and referential integrity constraints, and which are not?
d. Specify all the referential integrity constraints that hold on the schema shown in Figure 5.8.

 Figure 5.8

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AIRPORT Airport_code Name City State FLIGHT Flight_number Airline Weekdays FLIGHT_LEG Flight_number Leg_number Departure_airport_code Scheduled_departure_time Arrival_airport_code Scheduled arrival_time LEG_INSTANCE Flight_number Leg_number Date Number_of_available_seats Airplane_id Departure_airport_code Departure_time Arrival_airport code Arrival_time FARE Flight number Fare code Amount Restrictions AIRPLANE_TYPE Airplane_type_name Max_seats Company CAN_LAND Airplane_type_name Airport_code AIRPLANE Airplane_id Total_number_of_sea Airplane_type seats SEAT_RESERVATION Flight_number Leg_number Date Seat_number Customer_name Customer_phone