Bill is employed by a company to design and maintain custom software applications used by the company's employees to determine inventory levels. john is one of the employees who uses the software applications maintained by bill. these software applications are important for customer service because when customers call the company to place an order, very often the call is switched to john. john uses the software application to determine the inventory levels and then informs the customer if the order can be placed. john is the ______________ of bill. supplier external customer external supplier internal customer