Hi,
please discuss with your functional team and take source team help.
Once you got requirement along with base tables then you can create custom generic data sources.
Later based on ecc fields we can use correct or similar bw info objects.
if you the be info object name then at bw side use table - RSOSFIELDMAP.
try to see table contents with selection on IOBJNAM - give your info object name and execute it.
it may shows related ecc field and data source. by using data source you can debug at RSA3 source side.
thru that way also you can find base table for your fields.
Thanks