Design hierarchies such that lower levels have more members than higher levels
This rule analyzes dimensions to determine whether any hierarchies have an attribute at a lower level in the hierarchy that contains fewer members than an attribute at the level above.
A hierarchy where an attribute at a lower level has fewer members than an attribute at a higher level occurs because of one of the following reasons:
Frequently, this kind of hierarchy indicates that the levels are in the incorrect order. For example, a hierarchy where the [State] attribute is at a lower level than the [City] attribute does not have the attributes in correct order.
This kind of hierarchy might also indicate that the key columns of the lower level are missing a column. For example, suppose the [Year] attribute is at a higher level than the [Quarter Number] attribute. This hierarchy is missing a column and should instead have the [Year] attribute above the [Quarter with Year] attribute.
In either of these situations, this kind of hierarchy will lead to confusion for end users who are trying to use and understand the cube.
You should create hierarchies in such a way that attributes at lower levels of the hierarchy contain more members than attributes at the level above.