Simple Object Implementation

Hi,

We are migrating excel based functionality to SAP CRM. We created Simple Objects Z-table and configured in SPRO and its working fine.

Problem is how can we link simple object to other root object with custom relation. I have gone through SCN blogs and threads but i could not find linking of simple objects to other root objects.

Also how can we update custom table of simple object for initial load with around 250000 entries?

Thanks,

Ripal