Thanks Sander.. yeah I got confused with DSOs and Datasources in ECC 
After some search and study, I can see that there are 2 scenarios which provided by Informatica for SAP can be used in our case. 1. Business Content Integration (BCI) to extract data from Data Sources 2. ABAP program to extract directly from tables
Informatica Supports Delta extraction in both the cases.
Thanks again 
Regards,
Ashok Oleti