1) When defining the Consolidation Foundation View, CDS or Calculation view, what is the suggested HANA view technology?
It entirely depends on the way the model has been defined whether he should use the CDS or Calculation view. If the user wants to define a complete consolidation model which should integrate with BPC, then it is advised that user utilizes the Calculation view as the foundation view. This is because BW virtual provider will now only consumes Calculation views.
If the user defines a model only for some simple group reporting, then he does not require BPC functionalities such as manual journals, elimination, and so on. Then he should use CDS view as the foundation view. The advantage is that the user does need to touch BW and BPC technologies. And he can utilize S/4HANA Embedded Analytics for creating his customized reports.
There is absolutely no performance difference in using CDS and Calculation view. RTCMD can still provide you with the same CDS views for the easy consumption in S/4HANA side, even using Calculation view as the foundation view.
2) If Calculation view is selected, does this refer that we will go away from CDS view?
No, even upon using the calculation view as the foundation view, the user is still close to the CDS view. As a S/4HANA application, Real-time Consolidation leverages a lot of CDS views. RTCMD generates CDS views which are based on Calculation foundation view. A user can completely leverage CDS technologies irrespective of whether the foundation view is CDS or Calculation.
3) What's the difference between HDI view and Calculation view?
Post 1709 FSP02, the HANA Repository is replaced by HANA Deployment Infrastructure (HDI) Container. The terminology "HDI View" equals to the HANA Calculation view, only as a differentiation with the HANA repository based Calculation view. The source code of "HDI View" has been stored in ABAP side(S/4HANA), and is capable of leveraging the standard ABAP transportation.