"Algorithm" for requirement type/check instruction determination

material Master -> MRP type
sales order -> item category
OVZI: item category, MRP type -> search strategy

if search strategy is 0 or not defined:

  material master -> material type 

  MRP group:
     1) material master -> MRP group
     2) SPRO for MRP groups: material type -> MRP group
  
  strategy group from:
     1) the material master -> strategy group
     2) OPPU: MRP group -> strategy group
 
  OPPS: strategy group -> requirement type

else if Search strategy is 1 or 2:

  OVZI: item category, MRP type -> requirement type

endif  

OVZH: requirement type -> requirement class

OVZI, OVZH, etc are transaction names.

What is the difference between strategy 1 and 2 in OVZI? If one uses strategy 2 a check is made that the requirement type is in the list of allowed req. types. That list is built with all the values of requirement types set in the planning strategies included in the planning strategy group (as from the algorithm, the planning strategy group can be defined in the material master or in the MRP group).

One other thing is tricky. Although the item category/MRP type configuration for the requirement type is done in SPRO section:

• Sales and Dist. > Basic Functions > Availability check
  

there is the need to assign the item category/MRP type to schedule line categories in section:

• Sales and Dist. > Sales > Sales Documents > Schedule lines
  

This is core SD configuration. But it's also the basic for modeling the GATP in APO.

Also check OSS 547277 point 7.