|
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. ==Distributed applications== 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: # ''File Transfer Protocol'' (FTP) copies or moves whole files or database tables to each client so they can be operated on locally. This model is appropriate for highly interactive applications, such as document and spreadsheet editors, where each client has a copy of the corresponding editor and the sharing of such documents is generally not a concern. # ''Thin client'' applications present the interface of an application to users while the computational parts of the application are centralized with the affected files or databases. Communication then consists of ''remote procedure calls'' between the thin clients and a server in which uniquely designed messages specify a procedure to be called, its associated parameters, and any returned values. # ''Fat client'' applications perform all application processing tasks on client systems, but data is centralized in a server so that it can be managed, so that it can be accessed by any authorized client application, so that all client applications work with up-to-date data, and so that only the records, stream sections, or database tables affected by an application are transmitted. Client application programs must be distributed to all clients that work with the centralized data. The DDM architecture was initially designed to support the ''fat client'' model of distributed applications; it also supports whole-file transfers. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Distributed Data Management Architecture」の詳細全文を読む スポンサード リンク
|