transaction code: COMM_PRAPPLCAT.
hierarchies maintained here will be treated as 'Base Hierarchy', you can assign different base hierarchy for each product type.
only base hierarchy can be assigned with standard set type(delivered by SAP)
if you assign standard set type to a non-base hierarchy, Error message: Certain set types can only be assigned to the base categories Message no. COM_PRCAT095 will show up.
A product must be assigned at least to one category from the base hierarchy(base hierarchy for the specific product type)
when you create a new product, for the category field you must fill in a 'base category'. *any category from a base hierarchy is called a 'base category', afterwards you can assign any non-base categories as you wish.