Page 123 - Accounting Information Systems

94 PART I Overview of Accounting Information Systems

inventory update program reduces inventory levels by deducting the QUANTITY SOLD value of a trans-
action record from the QUANTITY ON HAND field value of the associated inventory record.

SEQUENTIAL FILE BACKUP PROCEDURES
An important characteristic of the sequential file update process is that it produces a new physical master
file. The new file contains all of the records from the original file, including those that were updated by
transactions and those that were not updated. The original master continues to exist. This feature provides
an automatic backup capability called the grandparent–parent–child approach. The parent is the original
master file, and the child is the newly created (updated) file. With the next batch of transactions, the child
becomes the parent, the original parent becomes the grandparent (the backup), and a new child is created.
Should the current master file (the child) become lost, damaged, or corrupted by erroneous data, a new
child can be created from the original parent and the corresponding transaction file.

Batch Processing Using Direct Access Files

Changing the file structures from sequential to direct access greatly simplifies the system. Figure 2-46
shows a system that is functionally equivalent to the one presented in Figure 2-44 but has been redesigned
to use direct access files. Notice the use of disk symbols to represent direct access storage device media.
The shift to direct access files causes two noteworthy changes to this system. The first is the elimi-
nation of the sort programs. A disadvantage of sequential file updating is the need to sort the transaction
file before each update run. Sorting consumes a good deal of computer time and is error-prone when very

FI GU RE
2-46 BATCH PROCESSING USING DIRECT ACCESS FILES

Unedited Sales
Transactions Orders

Edit
Errors

Edited Sales Accounts
Transactions Orders Receivable

Update
Inventory

Sales General
Orders Ledger

Billing and Bills
Reporting
Program Management
Reports