Because your starting point can be any level or combination of levels in the hierarchy, you can adopt either a top-down (centralized) or a bottom-up (decentralized) approach to planning. At runtime, the key figure values you maintain at one level are automatically distributed ¾ that is, aggregated and/or disaggregated ¾ throughout the planning hierarchy, thus ensuring data consistency among all planning levels. In other words, planning levels are interdependent. Only data at the lowest (most detailed) hierarchical level is stored in the database.