MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 21: OLE DB for OLAP Concepts
In a balanced hierarchy, the parent of each member comes from the level immediately above the member. A family tree is an example of a balanced hierarchy. Most hierarchies on the Time dimension are also balanced.
Ragged hierarchies are more common. In a ragged hierarchy, the parent of a member can come from any level above the level of the member, not just from the level immediately above.
OLE DB for OLAP supports both balanced and ragged hierarchies. The MEMBERS schema rowset has not only a parent name but also the level number of the parent. Similarly, the restrictions on this rowset enable you to browse not only by moving up and down the levels but also by moving up and down the inheritance tree.