The bean-managed persistence mechanism for entity beans imposes that each entity bean has a primary key which is to be used for uniquely identifying data to be loaded from the persistent storage. This primary key will so have to be unique for each BEAN INSTANCE. Also since ejb are not multithreaded , the application server when faced with the issue of concurrent requests generates multiple bean instances.Hence multiple bean instances can exist at runtime, which represent the same underlying data. However in such a situation , wont multiple bean instances have the same primary key ?????????????    More>>