Hi Ashok,
Let me try to answer your questions:
Q1. Will Informatica extract data directly from tables or from DSOs in the ECC system?
A1. A DSO is a persistent metadata object in BW. So you normally will not find DSOs in ECC. I think that Informatica will extract data directly from tables.
Possibly Informatica can connect to so called DataSources. A DataSource is an extraction program created by SAP or the customer. This is best practice way to extract data by BW or Data Services. A strong advantage is the packaging concept.
Q2. What would be the approach to extract the delta data daily from SAP and load into target (Hadoop in this case)
A2. DataSources often offer an out-of-the-box delta mechanism. Recently SAP also introduced the so called ODP (Operational Data Provisioning) framework. I don't know if Infomatica can connect to it or not.
If it does not answer your questions, please share the configuration guide / documentation which you have obtained. Please indicate where we can read the most important information.
Best regards,
Sander