Nodes of different colours represent the following:
Solid arrows point from a submodule to the (sub)module which it is
descended from. Dashed arrows point from a module or program unit to
modules which it uses.
Where possible, edges connecting nodes are
given different colours to make them easier to distinguish in
large graphs.
~ ~ ~ PURPOSE ~ ~ ~
this subroutine calls subroutines which read input data for the
databases and the HRUs