A fixed depth hierarchy is a series of many-to-one relationships, such as product to brand to category to department.  When a fixed depth hierarchy is defined and the hierarchy levels have agreed upon names, the hierarchy levels should appear as separate positional attributes in a dimension table. A fixed depth hierarchy is by far the easiest to understand and navigate as long as the above criteria are met. It also delivers predictable and fast query performance. When the hierarchy is not a series of many-to-one relationships or the number of levels varies such that the levels do not have agreed upon names, a ragged hierarchy technique must be used.