public class Tariff implements Serializable
{
   private ClientType clientType;
   private Calendar fromDate;
   private String name;
   private Double markUp;

//getters, setters, equals(), hashCode()...
}

public class CommissionableTariff extends Tariff
{
   private Double commission;
//getters, setters
}

public class NetTariff extends Tariff
{
//getters, setters
}

<class name="es.tariff.Tariff" discriminator-value="T">
    <composite-id>
       <key-many-to-one name="clientType" class="es.agency.ClientType" column="clientType"/>
       <key-property name="fromDate" type="date"/>
   </composite-id>
   <discriminator column="type" type="character" />
   <property name="name" type="string"/>
   <property name="markUp" type="double" length="12"/>   
   
   <subclass name="es.tariff.NetTariff"
       discriminator-value="N" dynamic-update="true"
       dynamic-insert="true">
    </subclass>
   
    <subclass name="es.tariff.CommissionableTariff"
       discriminator-value="C" dynamic-update="true"
       dynamic-insert="true">
       <property name="commission" type="double" length="12"/>
    </subclass>   
</class>

ClientType clientType = (ClientType)HibernateSession.currentSession().load(ClientType.class, new Long(rq.getClientTypeCode()));
         Calendar fromDate = rq.getTariffFromDate();
         Double markUp = new Double(NumberUtils.getDouble(rq.getTariffMarkUpInt(),rq.getTariffMarkUpDec()));
         String name = rq.getTariffName();

NetTariff nTariff = new NetTariff();
            nTariff.setClientType(clientType);
            nTariff.setFromDate(fromDate);
            nTariff.setMarkUp(markUp);
            nTariff.setName(name);
            
            HibernateSession.currentSession().saveOrUpdate(nTariff);
            HibernateSession.currentSession().flush();

public boolean equals( Object o )
   {
      if( o instanceof Tariff )
      {
         Tariff other = (Tariff) o;
         return (
               (this.clientType.equals(other.getClientType())) &&
               (this.fromDate.equals(other.getFromDate())));
      }

      return false;
   }

   public int hashCode()
   {
      return fromDate.hashCode() ^ clientType.hashCode();
   }