23.4.4. Content based discrimination

<class name="Person"
    discriminator-value="P">
    <id name="id" 
        column="person_id" 
        unsaved-value="0">
        <generator class="native"/>
    </id>
    <discriminator 
        type="character">
        <formula>
            case 
                when title is not null then 'E' 
                when salesperson is not null then 'C' 
                else 'P' 
            end
        </formula>
    </discriminator>
    <property name="name" 
        not-null="true"
        length="80"/>
    <property name="sex" 
        not-null="true"
        update="false"/>
    <component name="address">
        <property name="address"/>
        <property name="zip"/>
        <property name="country"/>
    </component>
    <subclass name="Employee" 
        discriminator-value="E">
            <property name="title"
                length="20"/>
            <property name="salary"/>
            <many-to-one name="manager"/>
    </subclass>
    <subclass name="Customer" 
        discriminator-value="C">
            <property name="comments"/>
            <many-to-one name="salesperson"/>
    </subclass>
</class>