Consider the following information in an airport database An airport is describe by its name and the city that the airport locates at Each airplane has a registration number and the date of production as its descriptive attributes Each airplane model is identified by a model number and has a capacity and a weight A technician is characterized by an ID, a name and a phone number Each airport accommodates a number of airplane models, and an airplane model may appears in several airports Each airplane is of a specific model, e.g. Boeing 737 A number of technicians work at the airport, but each technician works only at one airport Each technician is responsible for one or more plane models, and one plane model has one or more technician responsible for it Each airplane is periodically tested by a number of technicians. A technician may test several airplanes each year. The information, such as the test number, the test date, the testing result, is required to describe a testing of an airplane