  The composite systems can be non-uniquely decomposed into parts (subsystems).
Not all decompositions (structures) of a composite system are equally
physically relevant. In this paper we answer on theoretical ground why it may
be so. We consider a pair of mutually un-coupled modes in the phase space
representation that are subjected to the independent quantum amplitude damping
channels. By investigating asymptotic dynamics of the degrees of freedom, we
find that the environment is responsible for the structures non-equivalence.
Only one structure is distinguished by both locality of the environmental in
uence on its subsystems and a classical-like description.
