Defining DBD and PSB metadata to the generation utilities

When the IMS catalog is used, it stores metadata about data types, data structures, access methods, and much more. This metadata is derived from the database descriptors (DBDs) and program specification blocks (PSBs) that you create when you define your databases and application programs views to IMS.

Some of the metadata is database metadata, which describes the physical database. Other metadata is application program metadata, which describes how the application program views or uses the data in the database. Much of the application program metadata that you code in the DBD comes from the requirements of your application programs and artifacts like COBOL copybooks.

The following elements are examples of things that you can code in a DBD that are described by application program metadata:

• External names for segments and fields, which are specified on the EXTERNALNAME parameter when you define a segment or field
• Complex data elements such as arrays and structures
• Field data types and data marshalling characteristics
• Character encoding
• Alternative field maps for segments

Coding the elements described by application program metadata in a DBD consolidates the data requirements of your application programs in a single, trusted location: the IMS catalog. When the IMS catalog is enabled, the metadata in the IMS catalog can be queried and analyzed as you develop new application programs or assess the impact of changes to existing databases and application programs.

You define the metadata to IMS either by coding parameters in the DBD and PSB generation macro statements or by submitting DDL to IMS by using a tool such as the IMS Enterprise Suite Explorer for Development.