#
# This is how the tables relate to each other, in this 
# xample. The records for each table are shown in parens.
#
#          _____ table b  (ab)
#         /
#  table a  (aa)
#        \______ table c (ac)  
#		        |    \____table d  (ae, af)
#               |
#               |_____table e   (ag)
# 
# So traversing this tree once yeilds aa, ab, ac, ae, ag.
#    going down it again (because table d has two records)
#    gives  ab, aa, ac, af, ag.
#