How-to define CDS View/Entity to generate a BO with Header and Item

Dear Members,

I've a really simple scenario (on NW7.5 sp3). I've two self-defined DDIC tables: document header and item. I want to define CDS on top of them, and let the framework to generate the BO from it with the header and item node. I could manage to generate the root node from the header table, but the child item node was not generated. Do you have a CDS snippet with @ObjectModel annotations to realize this ? What are the requirements to do this ?

Thank you very much

Attila