R12 How to update the item cost according to either PO or AP in OPM

Hello

I am almost new in OPM Cost Managemente and in discrete manufacturing we have a program called Mass Edit where you can update the items cost according to a monthly average of PO or AP invoices.

Will you please give me an overview about OPM, because in Discrete Manufacturing we have BOM (Bill of Materials) for the recipies and CST (Cost Management).

I was wondering if we need to have two inventories one define in Discrete and another in OPM.

a) OPM Inventory

b) OPM Product Development

c) OPM Process Execution

d) OPM System Administration

e) OPM Cost Management