Do we need a SAP PI system to use SAP SRM enterprise services?
I am working in a project where we need to use some enterprise services like ([Maintain Purchase Request|http://wiki.sdn.sap.com/wiki/display/ESpackages/MaintainPurchaseRequest]) for SAP SRM 7.x. We have an ECC 6 system also in the landscape but the middleware is a non-SAP one. My question is that to be able to use the SRM and Enterprise Services, do we need SAP PI or SAP CE in place. Any help or useful clue/pointers is appreciated.