Filtering Records with Start Routine

Hello BW Gurus,

I want to load selected records from ODS1 to ODS2. ODS1 contains the Key Field Meter Reading Documents and characteristic Site (Installation).

I want to load only the three most recent MR Docs for each site. Most recent MR Docs are identified by higher MR Doc Number.

Anybody has ABAP code example to help me start?

Thanks

JLT