DRDA DDM command architecture reference

IMS supports the distributed data management architecture (DDM) of the Distributed Relational Database Architecture (DRDA). You can develop your own source DDM server that communicates with the IMS target DDM server to provide access to databases managed by IMS DB in DBCTL and DB/TM IMS systems.

The IMS documentation for the DDM architecture includes only the DDM structures that are required to connect to and communicate with IMS and the DDM structures that have been changed or defined by IMS.

For the complete documentation of the DDM, see DRDA, Version 4, Volume 3: Distributed Data Management (DDM) Architecture, which is available from The Open Group at www.opengroup.org.

The DDM architecture includes the following elements or terms:

  • Commands
  • Command objects
  • Reply objects
  • Reply messages

Each term, whether it is a command, command object, reply object, parameter, or message, is represented by a codepoint, a hexadecimal value that represents and identifies the component in communication between a source server and the target server. For example, the EXCSAT command is represented by X'1041', the EXCSATRD reply object is represented by X'1443', the SRVNAM parameter is represented by X'116D', and so on.

As an open standard, the DRDA specification requires that products that use the specification must conform to the conventions, protocols, standards, and so on, of its architecture. However, the DDM architecture that is a part of the DRDA specification allows products to create product-unique extensions, in which a product, such as IMS, uses a subset of the existing DDM-defined commands, parameters, and messages, as well as product-unique structures that are defined by the product. When creating a product-unique extension that has product-unique structures, the product must conform to the DDM architecture.

The product-unique extension for IMS conforms to both the DDM architecture and the DRDA specification. IMS uses a subset of the existing DDM-defined commands, parameters, and messages, as well as a variety of IMS-defined structures that conform to the DDM architecture, but are unique to IMS.