To answer myself, it is described in section 3.1.1 of the ejb 3 persistence spec. Regards, Milan Wölke View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3985495#3985495 Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&p=3985495