The concept of device integration means that your application does not need to know how a device is defined. Even if the underlying definition of the device is changed, you do not have to make any changes to your application.
Your application program accesses a device by name. When your application "prints" a map, the control information is sent by the user interface manager to the currently selected output device. The output device need not be a printer, it can be any of the output devices set up on your system database. If the device has an associated device driver, this is loaded into memory. DP4 then takes the map, formats the fields, and sends the resulting text to the device driver.
Input to your application program is sent to the current input field on the map. Where more than one input device is used, your application can check which input device returned the data.