Create an ER model for each of the following descriptions:

(a) Each company operates four departments, and each department belongs to one company. Each company has a unique name, and each department has a unique number and name.

(b) Each department in part (a) employs one or more employees, and each employee works for one department. Each employee has a number, name (including first and last name), date of birth, and age.

(c) Each of the employees in part (b) may or may not have one or more dependants, and each dependant belongs to one employee. Each dependant has a name, relationship to employee, and contact telephone numbers up to a maximum of three.

(d) Each employee in part (c) may or may not have an employment history. Each employment history has the name of the organization that the employee worked for and in what capacity, the start date and finish date for each employment.

(e) Represent all the ER models described in (a), (b), (c), and (d) as a single ER model. Provide any assumptions necessary to support your model.