tpham:
Layout requires the following functionality from Data Manager:

processing of events used by Layout (see Event_by_Layout.txt):
  modify graphical representation of objects
  modify graphical representation of connections


This functionality of Data Manager is required by Layout in
order for Layout to save its changes to the data. Although the
logic in Layout can still be tested without the specified
functionality of Data Manager being implemented, the Layout
module will have essentially no effect on the program without
this functionality.