This will try and list all possible "equivalence" cases that can happen in a model comparison. For each use case, we will consider
two models, "left" and "right".

a - 2-ways comparison - null to value
	a1 - 1-1 relation
	a2 - 1-n relation
	a3 - n-n relation
	a4 - recursive relation
	a5 - reference to new objects
	
b - 2-ways comparison - value to null

c - 2-ways comparison - change values
	c1 - change from and to existing objects
	c2 - change from existing object to an added one
	c3 - change from a deleted object to an existing one
	c4 - change from a deleted object to an added one

d - 2-ways comparison - multiple changes

e - 3 ways - left changes

f - 3 ways - right changes
	
