DP4 networking allows DP4 programs running on one machine to transparently access a DP4 database located on another machine by transferring calls to the database manager using network messages.
A number of different programs are used with DP4 networking. An alphabetical list of the various components and a summary of their use is contained in DP4 Networking Components. This topic introduces you to the most important ones.
There are two basic components, which usually have a different name for each operating system/network protocol combination.
The DP4 network requester or client is the principal client side component. To DP4 applications the DP4 network requester appears to be exactly like the regular DP4 database manager. The network requester routes calls to the DP4 database manager over the network to the second component:
The DP4 network manager receives calls from DP4 network requesters and passes them to the DP4 database manager. This is the principal server side component. To the database manager the network manager appears to be an ordinary DP4 application program.
A third component, the network router (AUXDISTR) is used in some Resilience configurations. The network router is used to select one or more servers to which to pass requests from applications. It can also manage distributed transactions - single logical transactions that update databases on more than one server.
Given an appropriate configuration of these components, a client program can log onto a database manager either on its own machine or on any other server machine on the network. Any machine may act as either a client or a server, or both a client and a server, with capabilities dependent on what DP4 networking components are loaded.
The selection of which server(s) an application uses can be made implicitly - as determined by the DP4 components loaded and the configuration in which they are loaded, and, (when there is one), configuration information on the local database. The various configurations are described in DP4 Networking Configurations.
Alternatively, the selection for a particular access can be made explicitly by the application program. A simple example of a program with explicit selection would be a program designed to move data, for instance price changes, from a remote database to the local database on a terminal. The program would use the Network API described in Information for Programmers.
Rather than running a traditional client-server configuration it is possible to run in a "thin client" configuration where DP4 programs are run on a server machine but use additional DP4 Terminal Server components to interact with the user on a client machine.
There are two additional client-side components for running DP4 terminal server (which is only supported on TCP/IP protocol):
There are no special server-side components required for DP4 Terminal Server, which is built into DP4 versions 4.523/4.619 or later. Machines used as servers for DP4 Thin Clients, are sometimes referred to as Application Servers.