Design the E-R diagram representing the entity sets, relationship sets, attributes, and ISA hierarchies of interest for the following application domain. For each entity set, determine the attribute (or attribute set) which is the key of the set. The MKT database stores information about a small supermarket in Toon Town. The supermarket is organized into several departments. Each department is characterized by a name and a department number. Each department is assigned a unique manager and several employees. A manager manages a single department and each employee works in a single department. Each employee is characterized by a name, a salary and a number of weekly hours. Each department carries a number of items. Each item is carried out by a single department; each item is characterized by a name, and a sale price. Items are supplied to the supermarket by suppliers. The same item can be supplied by different suppliers. Each supplier sets the price for each item it supplies. Each supplier is characterized by a name and an address. The supermarket allows customers to send orders. Each order includes a number of ordered items; for each item, the ordered quantity is also indicated (for example, three boxes of pasta). Each order is characterized by an order number and a date. Moreover, each order is associated with the customer who has placed the order. Each order is placed by a single customer; a customer can place multiple orders. Each customer is characterized by a name, an address and a balance. The database may also contain customers who have not yet placed an order.