ACCOUNT NUMBER and INVENTORY NUMBER are both secondary keys (SK) as neither of these keys uniquely identifies sales order records. For instance, there may be more than one sales order for a particular customer. Similarly, the same inventory item type may be sold to more than one customer. Hence, the values for these keys are not unique. Their purpose is to locate the corresponding records in the AR subsidiary and inventory master files.
A simplifying assumption in this hypothetical system is that each sales order record is for a single item of inventory. This one-to-one relationship is unrealistic because in reality one sales order could include many different inventory items. In Chapter 9, we will examine more complex file structures that permit the representation of one-to-many (1:M) and many-to-many (M:M) relationships that are frequently found in business transactions. At this point, however, avoiding this complicating factor will facilitate under- standing of both automated and re engineered systems. Figure 4-16 illustrates an automated sales order system that employs batch processing.1 The greatest impact from this low-end technology is seen in billing, inventory control, accounts receivable, and general ledger. These previously manual bookkeeping tasks have been automated. The two principal advantages of this are cost savings and error reduction. By automating accounting tasks, a firm can reduce its clerical staff and its exposure to many forms of errors. Other clerical and operational tasks