Whilst the database manager provides an interface between the application program and the database, the DP4 user interface manager, or terminal manager provides an interface between the application and the workstation. In this context, the workstation consists of the screen, the keyboard and the operating system on the machine.
The terminal manager insulates the application from the operating system and hardware in the following ways:
When the user presses a key, the user interface manager processes the keystroke, and sends the information to the application in a standardised form. You can modify the key translation table to reassign keys, such as redefining the help key to <F1> or <Ctrl><F3>
The user interface manager reads the layout of the screen from the currently selected map at runtime. If you change the text defined by the map (for example because you want to provide a localised version to run in another country), you do not need to change or recompile your application program. The application does not need to know if it is running in a text based environment or a GUI. The application may not even be running on the same computer as the terminal manager.
Devices are set up on the system database and are independent of the application. Your application selects a named device at runtime. The user interface manager then reads the device information and inputs from or outputs to the device. As a result, your application is device independent.
The DP4 User Interface is described in greater detail here.