Twist on this I just remembered. With entity caching, user types can be part of the FQN as well. Primary key of the entity is the last element of the FQN. A user type in an FQN is of course generally possible; entity caching is just a particular example where I've had to handle it with region-based marshalling. (The region portion of the FQN is only strings). View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4115363#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...