Test case hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<class name="ClassA" abstract="true">
<id name="id" type="long"><generator class="native"><param name="sequence">ClassA_seq</param></generator></id>

<many-to-one name="myClassB" class="ClassB" not-null="true" />
</class>

<class name="ClassB" proxy="ProxyB" abstract="true">
<id name="id" type="int"><generator class="native"><param name="sequence">ClassB_seq</param></generator></id>
<discriminator column="myType" />

<property name="name" type="string" />

<subclass name="ClassBSubA" discriminator-value="a" proxy="ProxyBSubA">
<property name="valueA" type="string" />
</subclass>

<subclass name="ClassBSubB" discriminator-value="iTunes" proxy="ProxyBSubB">
<property name="valueB" type="string" />
</subclass>
</class>

</hibernate-mapping>