I believe you can obtain this information from Hibernate. If you look at our EJB3 doco, you can see how to obtain a reference to a Hibernate Session or SessionFactory. Then from their, look at the Hibernate doco on how to get at metadata.
Thanks for the reply Bill,
I was afraid for this answers. I think it would be nice that metadata would be part of the (Sun) specification for EJB3. It makes it more transparant.