A data definition module (DDM) contains the description of a database file and the fields therein. Natural requires this description to access the data stored in the file from a Natural program.
For further information, see Data Definition Modules - DDMs and Natural and Database Access.
Accessing a Db2 Table in the Database Management System Interfaces documentation
Generating Natural Data Definition Modules (DDMs) - SQL Services - in the Database Management System Interfaces documentation
Protecting DDMs On Mainframes in the Natural Security documentation