Hibernate version: 3.0.2

Table description
TableA:
ID LONG (PK)
[...] other columns

TableB
ID LONG (PK)
[...] other columns

ATOB
ID LONG (PK)
ID_A LONG (FK to TableA)
ID_B LONG (FK to TableB)

Mapping documents:
Unidirectional many-to-many:
Exactly as in the documentation (page 74: 7.3.4 Unidirectional many-to-many association)

I have scanned the forum with no success for this, but I have the feeling I have read the solution somewhere (so I am very sorry that I still have to ask it).

1/ How should the mapping be in the above case?

2/ In case I use above mentioned unidirectional many-to-many association mapping (so ignoring the identity column) is there any drawback?

greatfully,