Page 99 - Accounting Information Systems

70 PART I Overview of Accounting Information Systems

purely real-time systems. In several chapters that follow, we will examine how these approaches are con-
figured to support specific functions such as sales order processing, purchasing, and payroll.
Updating Master Files from Transactions
Whether batch or real-time processing is being used, updating a master file record involves changing the
value of one or more of its variable fields to reflect the effects of a transaction. Figure 2-28 presents
record structures for a sales order transaction file and two associated master files, AR and inventory. The
primary key (PK)—the unique identifier—for the inventory file is INVENTORY NUMBER. The pri-
mary key for AR is ACCOUNT NUMBER. Notice that the record structure for the sales order file con-
tains a primary key (SALES ORDER NUMBER) and two secondary key (SK) fields, ACCOUNT
NUMBER and INVENTORY NUMBER. These secondary keys are used for locating the corresponding
records in the master files. To simplify the example, we assume that each sale is for a single item of in-
ventory. Chapter 9 examines database structures in detail wherein we study the database complexities
associated with more realistic business transactions.
The update procedure in this example involves the following steps:

1. A sales order record is read by the system.
2. ACCOUNT NUMBER is used to search the AR master file and retrieve the corresponding AR record.
3. The AR update procedure calculates the new customer balance by adding the value stored in the
INVOICE AMOUNT field of the sales order record to the CURRENT BALANCE field value in the
AR master record.
4. Next, INVENTORY NUMBER is used to search for the corresponding record in the inventory mas-
ter file.
5. The inventory update program reduces inventory levels by deducting the QUANTITY SOLD value
in a transaction record from the QUANTITY ON HAND field value in the inventory record.
6. A new sales order record is read, and the process is repeated.

FI G U RE
2-28 RECORD STRUCTURES FOR SALES,INVENTORY, AND ACCOUNTS RECEIVABLE FILES

Record Structure for
(PK) (SK) (SK) Sales Orders Transaction File

Sales Account Inventory Quantity Unit Invoice
Order Number Number Sold Price Amount
Number

(PK) Record Structure for AR Master File

Last
Account Name Address Current Credit Payment Billing
Number Balance Limit Date
Date

(PK) Record Structure for Inventory Master File

Inventory Quantity Reorder Vendor Standard Total
Number Description on Hand Point EOQ Number Cost Cost