It is tempting to try to use parent-child relationships to handle many-to-many relationships but Yukon has introduced a many-to-many relationship functionality that’s really cool. For example, using a geography hierarchy noted below, France and Spain both belong to a hierarchy of "Western Europe" and "EU"
Western Europe
Switzerland (SZ)
France (FR)
Spain (SP)
Lithuania (LI)
Switzerland (SZ)
France (FR)
Spain (SP)
Lithuania (LI)
EU
France (FR)
Spain (SP)
France (FR)
Spain (SP)
And the problem with many-to-many relationships is that you risk double-counting, double-summing of in this scenario. Well, to resolve this, you can use the reference of:
Instead of the above examples of Customer, Account and CustomerAccount; you would create a Region (Western Europe, EU), Country (SZ, FR, SP, LI), and a CountryRegion table which maps the many-to-many relationships between the country and region.
Denny Lee 
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