Hi Ali,
It is purely depends on how the system and events architect & solutions. You want to update from which system to which system.
I can give you standard approach...
Some events like below:
Shipping Line system -> SAP PI -> SAP ERP -> SAP EM
Some events directly update in both systems:
Shipping Line system -> SAP PI -> SAP ERP
Shipping Line system -> SAP PI -> SAP EM
Acknowledgement update:
SAP EM -> SAP ERP
Regards
GGOPII