How does Item Master get identified during Requisition Import or PO Creation

Summary:

How does Item Master Id get identified during Requisition Import or PO Creation.

Content (please ensure you mask any confidential information):

 For type-in Requisitions, or Requisitions created in external systems without Oracle MTL Item Id, I am looking for some information around the logic Oracle fusion uses to identify an itemId in procurement when importing a Req from external sources, or converting a Requisition into a Purchase Order.  Are there certain set of attributes fields which can be populated during the requisition import/or conversion into a purchase order from an Oracle Requisition to derive the MTL ItemId automatically ? We are hoping that if the correct ItemId is derived, the system will automatically pull the associated Unit Price, MFG Part