IMS DB Question:

DBDGEN control statements consists of Assembler Language macro statements. The macros are supplied by IBM in a library named IMSVS.MACLIB. DBDGEN control statements are normally coded by the DBA and submitted to the system with JCL. That invokes a cataloged procedure usually called DBDGEN. The DBDGEN procedure causes the DBDGEN control statements to the processed by the assembler producing the object module. The object module is then passed to the linkage editor which, in turn, stores a load module in another IMS Library called as IMS.DBDLIB or IMSVS.DBDLIB.

The DBD process is normally preformed only once for a database. All applications use the DBD in accessing the information on the database. A new DBD is normally created only if the physical nature of the database changes.