Hi guys, it seems to be a bug. Here it's the link to Hibernate bug tracker. It seems to happen when using both annotations and orm.xml. In fact, in my projects I had created two jars, one with annotations and another one without.
Originally posted by Mirko Bonasorte: According to you, it is an error of the book or an Hibernate bug?
I wouldn't call it a bug in Hibernate. Looks like the book missed out on that definition. Hibernate does make a mention about adding the schema declaration for persistence.xml (i would consider, it holds true for orm.xml too):
Be sure to define the grammar definition in the persistence element since the EJB3 specification requires the schema validation