  Some systematic general features of y-scaling structure functions, which are
essentially independent of detailed dynamics, are pointed out. Their physical
interpretation in terms of general characteristics, such as a mean field
description and nucleon-nucleon correlations, is given and their relationship
to the momentum distributions illustrated. A new relativistic scaling variable
is proposed which incorporates the momentum dependence of the excitation energy
of the (A-1) system, with the resulting scaling function being closely related
to the longitudinal momemtum distributions and being free from removal-energy
scaling violating effects.
