Extraction from legacy system

Hello Gurus,

My client wants me to load data from mainframe system to BW in near real time. They want me to use some ETL tool like Datastage, Infomatica... for doing that. Since I will have to use staging BAPI for doing extraction, I will have to handle delta at ODS object level( If I am not wrong only service API support queue delta extraction). But is delta handling at ODS object level effective in a near real time scenario?

I do not have any prior experience in staging BAPI.

If I use staging BAPI for data loading, will I have to write

function module for each info-object that I define Or are they already built in to staging BAPI?

Any help will be appreciated.

Thanks

Anand