How databases are defined to IMS

If your IMS system manages runtime application control blocks by using the catalog, you can define databases to IMS by issuing industry standard SQL statements. However, if your IMS system uses ACB libraries, you must code a macro that generates a DBD.

A DBD (database descriptor) is a series of macro instructions that describes the organization and access methods for a database, the segments and fields in a database record, and the relationship between types of segments. The use of macros to generate DBDs is required only for IMS systems that use ACB libraries.

If you enable the IMS system to manage application control blocks by using the catalog, you do not need to code and generate a DBD. Instead, you can use the IMS Enterprise Suite Explorer for Development to model the attributes of your database and issue DDL statements to update the IMS catalog. IMS uses the catalog data to manage the database descriptions internally.

Certain databases, such as IMS partitioned hierarchic direct databases, known collectively as High Availability Large Databases (HALDB), require you to define additional database characteristics in the RECON data set.

If you have the IBM® DB/DC (database/data communication) Data Dictionary, you can use it to define your database (except for DEDBs and MSDBs). The DB/DC Data Dictionary may contain all the information you need to produce a DBD.