At the central site of Philadelphia, the four files shown in the figure are being used by the ORDERENT application program.
At the central server, the CUSTMAST file is a physical file that is the primary file of customer data for all locations. The CUSTMST2 file is a logical file that is based on the CUSTMAST physical file. Using a logical file at the central server provides at least two advantages:
- The same program, ORDERENT, can be used without change by the central server and by each of the remote servers.
- The data can be accessed through a separate file and cannot keep a customer's primary record locked for the duration of the order.
The four files at the central site are used as follows:
- The CUSTMAST file contains all the data about all its customers. After a customer order is completed, the CUSTMAST file is changed with all the new information provided by that order.
- The CUSTMST2 file, which is a logical file at the central server, is used at the beginning of a customer order. When an operator enters a customer number, the program reads the customer data from the CUSTMST2 logical file, but the data actually comes from the primary file, CUSTMAST.
- The INVEN file contains the current quantities of all items available for sale to customers. When the operator enters an item number and quantity ordered, the corresponding primary item in the INVEN file is changed.
- The DETAIL file is a list of all the individual items ordered; it contains a record for each item and quantity ordered by customers.
