DEDB command codes for DL/I

The M, R, S, W, and Z command codes are only used with a DEDB.

Sample application program

The following examples are based on one sample application program—the recording of banking transactions for a passbook (savings account) account. The transactions are written to a database as either posted or unposted, depending on whether they were posted to the customer's passbook.

For example, when Bob Emery does business with the bank but forgets to bring in his passbook, an application program writes the transactions to the database as unposted. The application program sets a subset pointer to the first unposted transaction, so it can be easily accessed later. The next time Bob remembers to bring in his passbook, a program posts the transactions.

The program can directly retrieve the first unposted transaction using the subset pointer that was previously set. After the program has posted the transactions, it sets the subset pointer to 0. An application program that updates the database later will be able to tell that no unposted transactions exist. The following figure summarizes the processing that is performed when the passbook is unavailable and when it is available.

Figure 1. Processing for the passbook example
figure shows two segment chains both possessing seven segments. The segments are labeled B1 to B7. The first segment chain illustrates when the passbook is unavailable. B1 to B4 are posted and the position one pointer points to B4. The second segment chain illustrates when the passbook is available. All segments are posted and the position one pointer is equal to zero and does not point to any of the segments.