David,
> Anyway, I don't understand why when tables are built with this
> referential
> integrity the back-end doesn't fullfill any request posted on those
> tables.
Short answer: Because the international specifications for relational
databases, SQL-92 and/or SQL-99, do not work that way.
Longer Answer: You can use:
SELECT * FROM t1 NATURAL JOIN t2;
... to get the functionality you are talking about (provided that the
foriegn key reference has the same name in both tables).
-Josh