Distributed Data Management Architecture

Distributed Data Management Architecture (DDM) is IBM's open, published software architecture for creating, managing and accessing data on a remote computer. DDM was initially designed to support record-oriented files; it was extended to support hierarchical directories, stream-oriented files, queues, and system command processing; it was further extended to be the base of IBM's Distributed Relational Database Architecture (DRDA); and finally, it was extended to support data description and conversion. Defined in the period from 1980 to 1993, DDM specifies necessary components, messages, and protocols, all based on the principles of object-orientation. DDM is not, in itself, a piece of software; the implementation of DDM takes the form of client and server products. As an open architecture, products can implement subsets of DDM architecture and products can extend DDM to meet additional requirements. Taken together, DDM products implement a distributed file system.

The designers of distributed applications must determine the best placement of the application's programs and data in terms of the quantity and frequency of data to be transmitted, along with data management, security, and timeliness considerations. There are three client–server models for the design of distributed applications:

The DDM architecture was initially designed to support the fat client model of distributed applications; it also supports whole-file transfers.

The DDM architecture provides distributed applications with the following benefits:

DDM architecture is a set of specifications for messages and protocols that enable data distributed throughout a network of computers to be managed and accessed.

IBM's Systems Network Architecture (SNA) was initially designed to enable the hierarchical connection of workstations to IBM mainframe computers. The communication networks available at the time were rigidly designed in terms of fixed connections between a mainframe and its suite of workstations, which were under the complete software control of the mainframe computer. Other communications between mainframes was also in terms of fixed connections used by software defined for specific purposes. As communication networks became more flexible and dynamic, generic peer-to-peer communications were desirable, in which a program on one computer could initiate and interact with a program on a different computer.

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