@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="value_type",
   discriminatorType=DiscriminatorType.STRING
)
@Table(name="house_property_value")
@javax.persistence.SequenceGenerator(
   name="seq_house_property_value",
   sequenceName="s_house_property_value",
   allocationSize=1
)
public interface HousePropertyValue extends Serializable {
   @Id
   @GeneratedValue(strategy = GenerationType.SEQUENCE, generator="seq_house_property_value")
   public Long getId();
   public void setId(Long id);
   @Column(name="value_key", nullable = false)
   public String getValueKey();
   public void setValueKey(String valueKey);
   @ManyToOne (fetch = FetchType.LAZY, cascade = CascadeType.ALL)
   @JoinColumn(name = "fk_house_id", referencedColumnName = "id", nullable = false)
   public House getHouse();
   public void setHouse(House house);
   public Object getValue();
   public void setValue(Object value);
}

@Entity
@DiscriminatorValue("DATE")
@javax.persistence.SequenceGenerator(
   name="seq_house_property_value",
   sequenceName="s_house_property_value",
   allocationSize=1
)
public class HousePropertyDateValue implements HousePropertyValue {

   @Id
   @GeneratedValue(strategy = GenerationType.SEQUENCE, generator="seq_house_property_value")
   private Long id;
   private House house;
   private String valueKey;
   @Column(name="value_date", nullable=false)
   private Date value = new Date();
   public HousePropertyDateValue() {}
   public HousePropertyDateValue(Date value) {    this.value = value;    }
   public Long getId() {       return id;    }
   public void setId(Long id) {         this.id = id;    }
   public String getValueKey() {         return valueKey;    }
   public void setValueKey(String valueKey) {   this.valueKey = valueKey;    }
   public House getHouse() {        return house;    }
   public void setHouse(House house) {        this.house = house;    }
   public Date getValue()    {        return value;    }
   public void setValue( Date value )    {        this.value = value;    }
   public void setValue( Object value )    {        this.value = (Date) value;    }
}