the purchasing process begins in the data processing department,where the inventory control function is performed.the revenue cycle or the conversion cycle actually initiates this activity. when inventories are reduced by sales to customers or usage in production,the system determines it the affected items in the inventory subsidiary file have fallen to their reorder points.if so, a record is created in the open requisition file. each record in the open requisition file defines a separate inventory item to be replenished.the record contains the inventory item numbers, a description of the item, the quantity to be ordered, the standard unit price, and the vendor number of the primary supplier. the information needed to create the requisition record is selected from the inventory subsidiary record. the inventory subsidiary record is then flagged"on order" to prevent the item from being ordered again before it arrives.