ILE COBOL Programmer's Guide


Distributed Data Management (DDM) Files

An ILE COBOL file assigned to a device of DISK or DATABASE can refer to a DDM file.

A DDM file is a file on the local (or source) system that contains the information needed to access a data file on a target system. It is not a data file that can be accessed by a program for database operations. Instead, when an ILE COBOL program running on a source system opens a DDM file, the file information is used by DDM to locate the remote file whose data is to be accessed.

A DDM file is created by the Create DDM File (CRTDDMF) command. The DDM file is stored as a file object in a library, the same as any other file or object.

When an ILE COBOL program opens a DDM file, a DDM conversation with the target system is established. And, if the program is opening the DDM file to access records in the remote file, an open data path (ODP) to the remote file is also established.

DDM can be used to communicate between systems that are architecturally different. For example, although the architectures of the OS/400 system and System/36 are different, these systems can use DDM to access files in each other's database.

The following sections discuss the behavior that is unique to DDM files, and database files access through DDM files. Other topics about database files are discussed elsewhere in this chapter.


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