Rule Definition
One-to-many associations are easily the most important kind of association. In fact, its usage is discouraged when a simple bidirectional many-to-one/one-to-many will do the job. In particular, a many-to-many association may always be represented as two many-to-one associations to an intervening class. This model is usually more easily extensible. In a real system, you may not have a many-to-many association. Usually there is almost always other information that must be attached to each link between associated instances (such as the date and time when an item was added to a category) and that the best way to represent this information is via an intermediate association class. Moreover, changing the definition of a primary key and all foreign keys that refer to it is a frustrating task.

Remediation
In Hibernate, you can map the association class as an entity and map two one-to-many associations for either side.

Violation Code Sample

<class name="A" table="A"> 
    ...  
    <set name="B" table="B">  
        <key column="A_ID"/> 
        <many-to-many column="B_ID" class="B"/> // VIOLATION
    </set> 
</class>

Hibernate in Action (ISBN 1932394-15-X) p 220