When you create a dimension and if you are not restricted to a single hierarchy, a dimension can have more than one hierarchy. The only restriction on using hierarchies from the same dimension is that you cannot use one hierarchy for the rows, and another hierarchy for the columns in the same crosstab. If you need to use your hierarchies in this way then each hierarchy must be in a separate dimension.
An example of multiple hierarchies for the same dimension is the time hierarchy, which can be viewed by Quarter or by Month. These hierarchies are separate but are interchangeable, and are bound to the same underlying query.
Tip
You are not limited to two hierarchies in a dimension. A dimension may contain any number of hierarchies.
The following is the Time dimension as a single dimension with two hierarchies, one by Month and the other by Quarter:
The hierarchies are defined in Framework Manager as follows: