FBL3N - Urgent help!!

Hi SAP gurus,

I got a requirement to create a report from scratch using the tcode FBL3N.

For data extraction, I need to follow the data extraction logic used in FBL3N.

I found that RFITEMGL is the report program of FBL3N, but even after debugging, I am unable to find the logic of data extraction.

Please help me !!!!!!

Thanks and regards,

Lucy