  Van Glabbeek's linear time-branching time spectrum is one of the most
relevant work on comparative study on process semantics, in which semantics are
partially ordered by their discrimination power. In this paper we bring forward
a refinement of this classification and show how the process semantics can be
dealt with in a uniform way: based on the very natural concept of constrained
simulation we show how we can classify the spectrum in layers; for the families
lying in the same layer we show how to obtain in a generic way equational,
observational, logical and operational characterizations; relations among
layers are also very natural and differences just stem from the constraint
imposed on the simulations that rule the layers. Our methodology also shows how
to achieve a uniform treatment of semantic preorders and equivalences.
