NHibernate in Action, Working with persistent objects, Using business

Quote from book: "Notice that it’s almost never correct to override Equals() on a subclass and include another property in the comparison. It’s tricky to satisfy the requirements that equality be both symmetric and transitive in this case; and, more important, the business key wouldn’t correspond to any well-defined candidate natural key in the database (subclass properties may be mapped to a different table)."