Hierarchy of Functions
Most industry experts when discussing MRP II are referring to 10 or 12 discrete business functions from the highest level of planning (business planning) to the lowest level of execution (purchasing & receiving).
Each management planning level receives its vision and constraints from the prior level. Decisions are "pushed down" (top-down) through the hierarchy and performance measurement information is pushed back up (bottom-up) to compare the actual performance with the planned performance. When there is a discrepancy between actual performance and planned performance, replanning is done at the appropriate level. This on-going process of top-down, bottom-up replanning can best be visualized as a circular joining of the three words: Plan, Execute, and Measure.