In the Purchasing department at one company, a purchase request may be assigned an expediter within the Purchasing department. This expediter follows the purchase request through the entire purchasing process and acts as the sole contact person with the person or unit within the company buying the goods or services. The Purchasing department refers to its fellow employees buying goods and services as customers. The purchasing process is such that purchase requests from certain special customers must go out for bid to vendors, and the associated Request for Bids for these requests must be approved by the Purchasing department. If the purchase is not by a special customer, the product or service can simply be bought from any approved vendor, but the purchase request must still be approved by the Purchasing department, and the department must issue a Purchase Order. For “special customer” purchases, the Purchasing department can issue a Purchase Order once the winning bid is accepted. List the relevant entities and attributes, and draw an E-R diagram for this business process. List whatever assumptions you must make to define identifiers, assess cardinality, and so on.