OBD2 is a USA standard, closely related to EOBD, which is the European standard.
With this standard you can read codes and data and reset codes on all makes.
Unfortunately for you on diesels in Europe from model-year 2004 on.
These code readers will NOT work on your car.

Can-Bus is a method of connecting several ecu's with only 2 wires.
A bit similar to a Network with several PC's.
It is used on "newer" vehicles for diagnostics, but not on your car.