Devices are set up on your DP4 system database using DFSETUP. Devices are defined in a hierarchical fashion in DFSETUP, with the Device Group at the highest level. The Device Group is then further defined in terms of component input and output devices. The process of creating a device group with DFSETUP is described in Configuring a Device Group. Applications do not use CODS (component output devices) directly but PODs (parameterised output devices). However, the interface between the DP4 Terminal manager and the OSDI uses the COD information directly. Applications do use input devices directly, as nothing would be gained by an abstraction equivalent to the one between CODs and PODs.
Typically, although not always, an OSDI handles just one Device Group (such as a printer or Point of Sale (PoS) terminal), and applications that use the OSDI will only access PODs belonging to that device group, (and possibly device groups that do not require an OSDI).
A Device Group (such as our DP4 Till) may contain several output and input devices. The example DP4 Till has two input devices (keyboard and scanner) and several output devices (printers, drawer, and so on).
The following diagram shows a Device Group, and the relationship between Device Group, CODs, PODs and input devices: