Parts of DDM: DDM file

A system object with type *FILE exists on the source server to identify a remote file. It combines the characteristics of a device file and a database file. As a device file, the DDM file refers to a remote location name, local location name, device name, mode, and a remote network ID to identify a remote server as the target server. The DDM file appears to the application program as a database file and serves as the access device between a source server program and a remote file.

A DDM file is a file on the source server that contains the information needed to access a data file on a target server. It is not a data file that can be accessed by a program for database operations. Instead, when a source server program specifies the name of a DDM file, the file information is used by DDM to locate the remote file whose data is to be accessed.

DDM file information is based on locations. The remote location where the remote file is located is specified using the remote location name (RMTLOCNAME) parameter on the Create DDM File (CRTDDMF) or Change DDM File (CHGDDMF) commands.

The remote file name specified on the CRTDDMF or CHGDDMF commands must be in the format used by the remote system.

Another use of the DDM file is to submit control language (CL) commands to the target system to run on that system. In this case, the remote file normally associated with the DDM file is ignored.

• Create a DDM file using SNA
  You can create a DDM file that uses SNA as the communication protocol for connecting with the remote system.
• Create a DDM file using TCP/IP
  You can create a DDM file that uses TCP/IP as the communication protocol for connecting with the remote server.
• Create a DDM file using RDB directory entry information
  You can create a DDM file that uses the remote location information from a relational database (RDB) directory entry.
• Example: Use the basic concepts of DDM in an APPC network
  This topic presents a sample application that uses DDM to access a remote file.
• Example: Use the basic concepts of DDM in an APPN network
  The Advanced Peer-to-Peer Networking^® (APPN) support of an iSeries™ server can be used to allow DDM access to systems not directly connected to the local server.