5.13. DataBase Consider the relation CLASS(Course#, Univ_Section#, Instructor_name, Semester, Building_code, Room#, Time_period, Weekdays, Credit_hours). This represents classes taught in a university, with unique Univ_section#s. Identify what you think should be various candidate keys, and write in your own words the conditions or assumptions under which each candidate key would be valid.

AIRPORT Airport code Name City State FLIGHT Flight number Airline Weekdays FLIGHT LEG Right 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 Right number Fare code Amount Restrictions AIRPLANE TYPE Airplane type name Max seats Company CAN LAND Airplane type name Airport code AIRPLANE Airplane d Total number of seats Airplane type SEAT RESERVATION Light numbor numbord Seat number Customer nane Customer phone Figure 5.8 The AIRLINE relational database schema