Data Source Migration in BI 7.0

Hi experts,

What is Migration , explian in detail about Data Source Migration in BI 7.0 ? How we can Migrate DS from 3.5 to 7.0 .

what is that With export and with out export and Direct Data Access and Real time data acquisition , how it will work ?

Plz explian in a detail manner, i will assign points for ur valuable answers.