Textbook: database systems a practical approach to design implementation and management

2.10 Create an ER model for each of the following descriptions: (a) Each company operates four departments, and each department belongs to one company. (b) Each department in part (a) employs one or more employees, and each employee works for one department. (c) Each of the employees in part (b) may or may not have one or more dependents, and each dependent belongs to one employee. (d) Each employee in part (c) may or may not have an employment history. (e) Represent all the ER models described in (a), (b), (c), and (d) as a single ER model