Joined-subclass is a mapping strategy in Hibernate and NHibernate that is also known as "Table per subclass".
Joined-subclass mapping is a mapping strategy in Hibernate and NHibernate where a superclass A is mapped to its own table and all subclasses that extend A is mapped to their own table, but with a join to A's table. Only the properties defined at each level in the inheritance hierarchy will be stored in corresponding columns in each class' database table.
When selecting a derived class B from the database, Hibernate does a select on A with a left outer join on B as well as all other classes extending from A. Depending on which left outer join returns any data, Hibernate constructs a new instance of the correct class (in this case, B) and fills it with data from table A and B.
