Initial Conceptual Design of the COMPANY Database
We can now define the entity types for the COMPANY database, based on the requirements described . After defining several entity types and their attributes here, we refine our design after we introduce the concept of a relationship. According to the requirements listed , we can identify four entity types—one corresponding to each of the four items in the specification:
1. An entity type DEPARTMENT with attributes Name, Number, Locations, Manager, and Manager_start_date. Locations is the only multivalued attribute. We can specify that both Name and Number are (separate) key attributes because each was specified to be unique.
2. An entity type PROJECT with attributes Name, Number, Location, and Controlling_department. Both Name and Number are (separate) key attributes.
3. An entity type EMPLOYEE with attributes Name, Ssn, Sex, Address, Salary, Birth_date, Department, and Supervisor. Both Name and Address may be composite attributes; however, this was not specified in the requirements. We must go back to the users to see if any of them will refer to the individual components of Name—First_name, Middle_initial, Last_name—or of Address.