Format of records in the IMS catalog database

The IMS catalog database contains a unique record for each PSB and DBD defined during ACB generation. Each type of record, and each type of segment within a record, has a predefined format.

The catalog database segment types are grouped into four different data set groups (A - D) based on how frequently that segment type is accessed in database queries. The most frequently accessed segment types, such as the root segment type (HEADER), are located in data set group A. The least frequently accessed segment types, such as user remarks segments, are grouped in data set D.

Some segment types in the catalog database, such as DBDHXXX, are not currently used and are reserved for future development. The segment definitions are included in the catalog to allow for the implementation of future service and development enhancements without an unload and reload of the catalog database.