OLAP cubes can be much more complex than this example. For any set of independent
dimensions, there may be more than one measure (e.g., units sold, and revenue).
These different measures are often collectively referred to as the Measures dimension.
Moreover, each independent dimension typically has a hierarchy of levels.
For example, a Location dimension might have regions at its top level, composed of
states at the second level, with cities at the third level, and stores at the fourth level.
Similarly a Time dimension may be decomposed into Years, then Quarters, then
Months, and then Days. Finally, the Item dimension may be decomposed into categories
and then items.