I am trying to understand how to migrate data domains and .lar files from Endeca 3.0 to Endeca 3.1 with minimal efforts. Can I use the same data indexes from 3.0 into 3.1, if not can I run the same graphs in new integrator. Does Lar files work between two version given they have same data set/data source names.
Studio does not generally support importing .lar files that were exported from a different version.
There are also some significant differences in 3.1, in particular the addition of data sets (called collections in Endeca Server), which are required for Studio data, as well as to some of the components. So you will in any case be required to make some changes to your applications.
You'll need to follow the migration instructions for Endeca Server, Integrator, and Studio.
The Endeca Information Discovery page on OTN (Endeca Information Discovery - Documentation) contains links to the documentation sets for all of the Endeca Information Discovery releases.
For each release, click the Endeca Information Discovery Link, which displays a landing page with the full documentation set (Endeca Server, Integrator, and Studio).
On each landing page are links to the migration guides for each of the products.