Hi Harsha
There are at least three types of interfacing them. We have implemented both of them with the help of SAP MII. Very briefly, they are:
1) Interfacing the SCADA/DCS alarms with SAP Notifications. You build your own logic and MII will do the translations of alarms into SAP Notifications.
2) Although most of the DCS/SCADA systems generate measurement readings, and these readings are captured in DATA HISTORIANS, a selective and/or filtered reading of these measurement might be copied into SAP. (If you want to trigger some condition based or counter based maintenance).
3) BI/BW can be used to link and report the measurement readings from the historians with SAP Breakdown Notifications. This might give you a better visibility on correlations between measurement readings and breakdowns.
I hope this will help.
Regards