Question 4. ER model (20 marks). The A-Star consulting firm has decided to build a database. The company has hired you to design the database. Requirements are as follows. . Clients are given a unique client-ID. Other client details including name, address and telephone number are also recorded. A-Star has several departments. Each department is described by a unique name address and contact phone number. Each department must have a manager and has many employees. A manager can only manage one department. . Each employee of A-Star has a unique employee ID, name, and birth date. An . An employee is assigned as the consultant for a group of clients. But a client has . Once signed up, clients book consultation sessions with their consultant. All employee must belong to a department. only one consultant. consultation sessions for a client are numbered sequentially as 1, 2, 3, etc. and the details for consultation sessions are also recorded, including date, time and topic. A-Star has vehicles for visiting clients. Each vehicle has a registration number, model, and year the vehicle was made. Consultants book vehicles for consultation sessions with clients. The database is aimed to Keep track of data for departments, employees, vehicles and clients. Keep track of the consultation sessions for clients and vehicle usage for booking vehicles for consultation. Keep track of scheduled consultation sessions for consultants. According to the requirements and design aim, give an Entity Relationship (ER) diagram for the database, making assumptions where necessary. You must represent entities, relationships and their attributes, and all applicable constraints in your ER diagram. Explain any constraints that can not be expressed in the ER diagram