23.4.5. Associations on alternate keys

<class name="Person">
    <id name="id">
        <generator class="hilo"/>
    </id>
    <property name="name" length="100"/>
    <one-to-one name="address" 
        property-ref="person"
        cascade="all"
        fetch="join"/>
    <set name="accounts" 
        inverse="true">
        <key column="userId"
            property-ref="userId"/>
        <one-to-many class="Account"/>
    </set>
    <property name="userId" length="8"/>
</class>
<class name="Address">
    <id name="id">
        <generator class="hilo"/>
    </id>
    <property name="address" length="300"/>
    <property name="zip" length="5"/>
    <property name="country" length="25"/>
    <many-to-one name="person" unique="true" not-null="true"/>
</class>
<class name="Account">
    <id name="accountId" length="32">
        <generator class="uuid"/>
    </id>
    <many-to-one name="user"
        column="userId"
        property-ref="userId"/>
    <property name="type" not-null="true"/>
</class>