a> annotations.
 It is used to map composite foreign keys.

 <pre>
    Example: ValuedCustomer subclass

    &#064;Entity
    &#064;Table(name="VCUST")
    &#064;DiscriminatorValue("VCUST")
    &#064;PrimaryKeyJoinColumns({
        &#064;PrimaryKeyJoinColumn(name="CUST_ID", 
            referencedColumnName="ID"),
        &#064;PrimaryKeyJoinColumn(name="CUST_TYPE",
            referencedColumnName="TYPE")
    })
    public class ValuedCustomer extends Customer { ... }
 </pre></div>
<dl>
<dt><span class="si