The representation of a physical device as an application object may be extended to encompass any external entity with which an application must interact. Suppose that an application executing in a programmable workstation must interface with a number of server applications executing in a System/370 host, using the SRPI interface. The host system may be regarded as a logical entity, and a single application object created to interact with that entity. All communications-related and interface-specific code may then be encapsulated within that object, and other objects within the application need not concern themselves with the details of the SRPI communication. A message passed to the application object by a requesting object elsewhere in the application will contain the name of the server application to be invoked, and the data to be passed to the server application. A return message from the host-interaction object will contain the reply data from the server application.
Figure "Encapsulation of Host Interaction Within Application Object"
The isolation of programming interfaces and protocols specific to the communications architecture, within the "Host" application object provides an easy means of insulating the remainder of the application from changes to communications network configurations or to the remote system itself. Such changes would only require modification to the "Host" object.