Adams, Ives, and Scott Incorporated is an agency that specializes in representing clients in the fields of sports and entertainment. Given the nature of the business, some employees are given a company car to drive, and each company car must be assigned to an employee. Each employee has a unique employee number, plus an address and set of certifications. Not all employees have earned one or more certifications. Company cars are identified by their vehicle id, and also contain a license plate number, make, model, and year. Employees represent clients. Not all employees represent clients, while some employees represent many clients. Each client is represented by one and only one employee. Sometimes clients prefer one another to use Adams, Ives, and Scott to represent them. A given client can refer one or more other clients. A client may or may not have been referred to Adams, Ives, and Scott by another client, but a client may be referred by only one other client. Each client is assigned a unique client number. Additional attributes recorded for each client are the name, address, and date of birth?
Draw an ER diagram that shows the entity types and relationship types for Adams, Ives, and Scott. While you must name each relationship type and define its structural constraints, it is not necessary that you supply role names.
It is possible that some students may model CERTIFICATION as an entity type instead of a multi-valued attribute and then establish a relationship with an m:n cardinality ratio between EMPLOYEE and CERTIFICATION. This was a good alternative, although in doing so, it is necessary to invent an attribute for the CERTIFICATION entity type since none was given in the problem.