Sample NH code which shows how to extend the domain model.
Instructions
Create two databases "Test" and "ExtendedTest"
Run scripts "NhibernateTest.sql" and "ExtendedNHibernateTest.sql" respectively on these databases
This has got two projects "NHibernateTest", "ExtendedNHibernateTest", the first one uses the normal code model and second one uses the extended core model