Interface with three system involved

Hi Experts,

Could you please help me to figure out a way to develop an Interface in which a three systems :

1. Websrvice Consumer (The initiator - say System A ) ,
2. SAP ECC (Source of Data, say System B) &
3. Oracle database (say System C).

I have to Pull records from SAP ECC's table and update in the Oracle database when my System A calls the webservice.

What should be my approach?

Thank you!

Best Regards,
Prabhat.

UPDATE: Also for another interface where in System A is initiator (again) but System C(oracle db) will the source and System B(ECC) will be Reciever.