PO vs Requisition amount check

Dear all,

Please suggest is there any standart functionality for nest cases:

1) If PO amount is greater then Requisition amount then logically PO can not be approved if Requisition amount is not changed and Requisition reaaproved. Or something like this. The main idea that PO or Requisition should be reapproved in such cases.

2) If amount of PO created from Oracle Sourcing Application is greater then Requisition amount then logically PO can not be approved if Requisition amount is not changed and Requisition reaaproved. Or something like this. The main idea that PO or Requisition should be reapproved in such cases.