How to generate new records using export datasource

Hi

I have an ODS with the fields field1, field2 and field3. I have another ODS say ODS2 that has the fields field2, field3 and field4. Now for each record in ODS1 I have to insert multiple records in ODS2 from ODS1 and also populate field4 of ODS2 by fetching some values from a ztable using some logic.

I have created an export datasource of ODS1 and I am trying to do the coding in the start routine of ODS2, is this correct? and since the data package structure does not have the field4 how can i populate this field in ODS2?

Regards,

Sujai