  There are many formalisms to describe quantum decoherence. However, many of
them give a non general and ad hoc definition of "pointer basis" or "moving
preferred basis", and this fact is a problem for the decoherence program. In
this paper we will consider quantum systems under a general theoretical
framework for decoherence and we will present a tentative definition of the
moving preferred basis. These ideas are implemented in a well-known open system
model. The obtained decoherence and the relaxation times are defined and
compared with those of the literature for the Lee- Friedrichs model.
