  We study the out of equilibrium dynamics of several models exhibiting aging.
We attempt at identifying various types of aging systems using a phase space
point of view: we introduce a trial classification, based on the overlap
between two replicas of a system, which evolve together until a certain waiting
time, and are then totally decoupled. We investigate in this way two types of
systems, domain growth problems and spin glasses, and we show that they behave
differently.
