The AR update program posts to accounts receivable by sequentially matching the
Account Number key in each sales order record with the corresponding record in the AR-SUB master file. This procedure creates a new AR-SUB master file that incorporates all the changes to the customer accounts that are affected by transaction records. The original AR-SUB master file remains complete and unchanged by the process. The creation of a new and separate master file is a characteristic of sequential file processing. A side benefit of this is the automatic creation of a backup version of the file being updated. Figure 9.2 illustrates this method with some sample records.