I would like to share a small information which I experienced couple of days back in my project.
I had a requirement to extract data from 0FC_OP_01 DataSource in my project. I activated the datasource and when checked in RSA3, zero records were extracted. Later when I checked in the DFKKOPBW (OI Extraction) table in SE16, it had no data.
I found the solution to pull data into DFKKOPBW table.
We have to perform the mass run activity from t-code FPBW by giving the Date ID and Identification. It extracts the open items data from base table DFKKOP table to DFKKOPBW table.
Later check the DFKKOPBW table in SE16, it shows records.
Check in RSA3:
Later you can follow the basic steps of replicating in BW and designing the flow as per the project demands.
This is how you can extract data into 0FC_OP_01 (FI-CA Open Items on Key Date) DataSource.