HCM Form Scenario Integrate with FPM in WD ABAP

Can anybody help me out with how the HCM form scenario is integrated with the FPm for WD ABAP?

I am facing a problem how data is coming in the web dynpro. I debugged and found that it is coming from standard method. But not sure how and exactly where the data is being fetched and exactly where the form scenario is attached for the specific FPM.