Redundent wincc+client+OPC XML DA??

Dear All,

My config as follows.

- 1 pair of Redundent WinCC
- 1 WinCC Client
- OPC XML DA installed on client
- MES will access Wincc Data over OPC XML DA.

Q:
- how / can MES access historic data of WinCC( tag logging data)??
- Whatever tags MES accessing, it must be on Wincc client / can be on wincc server ( because normally all tags will be on server)??
- as per the attached picture, any explanation is available for the mentioned services....especially for get properties??

Thanks