Related tables for collection of collections

Hi,

In my Process Entity (PE), there is (among ohers) an attribute CA which is a collection of entities A.

Entity A has (among others) an attribute CB which is a collection of entities B.

What is the best (easiest) way to design a form for the following scenario ?

In the same form, have one table TA for collection CA and one table TB for collection CB in a way that when I select a row (A entity) on table TA, the table TB displays the list of items (B entities) from CB attribute corresponding to the selected row in TA.

Complementary question : is there a way to set an action when selecting a row in a table (with expression accessing the selected row = entity instance) ?

In advance, thanks for your advise.

Regards,

Walter