Have a look at the SAP Condition Based Maintenance RDS (http://service.sap.com/rds -> Lines of Business -> Asset Management -> Asset Visibility and Performance -> Condition Based Maintenance) or you can directly go here:
http://service.sap.com/rds-cbm
This will talk about how best to integration an OT system like the OSI Soft PI historian with the SAP PM backend. There's more to simply calling the service and for example the OSI Soft PI/AF environment will not know the details of the equipment as defined in the SAP PM backend.
Sam
