Hi,
It is possible in CMP and it is a peice of cake. You need to do following things :
1. create class which contains all required attribute of your composite PK and make it sure that this class implement serializable interface.
2. override equal and hashcode as per your business rule.
3. mention your class name with fully pkg name in descriptor of your entity.
4. I think tag called comp-pk ... but check in spec.
for eg.
class myPK implements Serializable
{
Intger col1;
String col2;
Inetger col3;
.... getter and setters
.. equals and hashcode....
}
hope that this help you...
Sunil