A hierarchy defines one of two paths through a dimension.
For more information about dimensions, see Dimensions (PDM).
The path are the following:
an organizational path - describes a traversal pattern through a dimension, from the most general to the most specific attribute of the dimension. It is an ordered subset of the attributes.
a consolidation path - represents a consolidation of attributes. For example, a Time dimension with a base periodicity of days might have a hierarchy specifying the consolidation of days into weeks, weeks into months, months into quarters, and quarters into years.