Inter-document communication(MFC)

Have pitty on me, I am new at this stuff. Currently I have about 5 documents each representing a different subsytem, along with a view showing the status of these subsytems. What I need to do is that when the data in one of these subsystems changes it needs to be verfied by a corosponding change in another sub-system. Also when an error condition arrises I need to send some info to a manager which is also a document. Is there a way to get at the other documents in the system from within a document? I thought using the global app object but could not figure it out.

Am I just way off base here? Should I maybe be using one document which "has a" bunch of sub-systems classes which know how to draw themselves in a view. Then this one document will have a view representing each sub-system?