How to create a new object with an aggregated reference to an existing object?

Hello community:

In my contract I have defined an object with an aggregated relationship to another object (complex data), my problem starts when in UI designer I show a table of existing objects (aggregated object) to the user for select which object will be referenced by the new object. Do you have any clues to do that? In particular, to create a new object linked to an existing object in DB. In all cases I'm using BDM accesors.

Regards...

-- Pablo