Unknown primary-key class
When writing an entity bean for Enterprise Java Bean Version 2.0, the minimum requirements usually include a primary-key class. However, in some cases you might choose not to specify the primary-key class for an entity bean with container-managed persistence. Perhaps there is no obvious primary key, or you want to allow the deployer to select the primary key fields at deployment time. The primary key type is usually derived from the type used by the database system that stores the entity objects, and you might not know what this key is.
So, the unknown key type is actually a type chosen at deployment time, making it changeable each time the bean is deployed. Your client code must deal with this key as type Object.
Currently, WAS supports top-down mapping and enables the deployer to choose String keys generated at the appserver. For an example of how to use this function, see the Samples library.