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Analysis of IMS Data Base Descriptors (DBD) Delete Rules for Change Data Capture Exit compatibility Disclosure Number: IPCOM000189294D
Original Publication Date: 2009-Nov-04
Included in the Prior Art Database: 2009-Nov-04
Document File: 5 page(s) / 33K

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The current invention addresses the problem of validating that the Change Data Capture exit can be used by subject databases by reading the DBD source code and doing the following: 1) Validating that the define Delete rules are compatible with Change Data Capture 2) Coding a new copy of the DBD source that includes the following: a) A re-coded Delete Rule for the segments which are incompatible, if desired b) Addition of the EXIT= parameter to the DBD source code.

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Analysis of IMS Data Base Descriptors (DBD) Delete Rules for Change Data Capture Exit compatibility

The following invention saves time and avoids unnecessary effort for determining whether database definitions can support the Change Data Capture exit and performs the necessary DBD changes to support the exit.

With the Information Management System (IMS) database manager product,
as with most other DBMS, logging of changes to database records is a basic function which has been supported since early in the inception of the product. Initially, a complete snap-shot of the data base record was written to the log,
along with descriptions of the type of operation involved, and before/after images of the records when applicable. However, database update is only one of a
large number of processes which are written to the log. As more and more operations were developed and written to the log, the volume of data contained on the log increased such that implementations were changed to minimize the data written to the log where such could be made terser. One of the changes included minimizing the data contained on a database update log record from complete record images to just a tersed copy of the actual data fields which were modified. Such tersed copies of the record images were fine when the log records were used for data-integrity purposes such as database recovery should a database require backout.

However, over time other uses of the log and the database record data were developed such that the terse data was not sufficient. Some installations or even applications within installations required complete images; however, many other installations or applications did not. To accommodate those installations which required complete images, while also concurrently accommodating those installations which required record terseness for log efficiency, an option was developed to
allow selective implementation of logging the complete database record. The mechanism for selecting the complete record logging is the Change Data Capture Exit parameter (EXIT=), specified at the database and/or segment level in the Database Descriptor (DBD) control block describing the database.

Among the types of databases and DBDs are physical and logical databases. Logical databases are alternate representations of one or more physical databases. Data contained in the databases can be altered by accessing
the physical database directly, or through the logical database representations; however, there can be restrictions on what processes can be performed through the logical databases.

One such restriction is the mechanism for deleting records. The rules for deleting segments are specified at the database or segment level. There are multiple options which can be specified: RULES=P (physical), RULES=L (logical), RULES=V (virtual), RULES=B (bidirectional virtual)

When RULES=P is specified, the logical child segment must be logically