Inheritance and Foreign Keys

Here's my situation: I have the following relation

table A -----<>------ table B
1:N

I created the two tables, and a foreign key from A into B. Now I want to
create other tables that inherit from B, but I want that the relation
exists for all of them. For that, I created another table, C, that had
just one field and inherited from B. No errors showed up, but it didn't
complain when I inserted some data into C without the corresponding one
in A!!

Is it possible to do what I intended?

Thanks

--
Nelio Alves Pereira Filho
IFX Networks - www.ifx.com.br
+55 11 3365-5863
nelio(at)ifx(dot)com(dot)br