class A
{
   String id;
}

class AA extends A
{
}

class BA extends A
{
}

abstract class CA extends A
{
}

class ACA extends CA
{
}

class BCA extends CA
{
}


class A is in  table T_A
+-------------------------------
| TABLE T_A
| -------------------------------
| ID_A NUMBER(28) not null
+-------------------------------

calss AA is in table T_AA
+-------------------------------
| TABLE T_AA
| -------------------------------
| ID_AA NUMBER(28) not null
+-------------------------------

class BA is in table T_BA
+-------------------------------
| TABLE T_BA
| -------------------------------
| ID_BA NUMBER(28) not null
+-------------------------------

class CA, ACA, BCA are in table T_CA 
... where table  T_CA contains a column for discriminator TYPE_CA, so I can hava a ACA or a BCA
+-------------------------------
| TABLE T_CA
| -------------------------------
| ID_CA NUMBER(28) not null
| TYPE_CA varchar(5) notnull
+-------------------------------


I WANT ( skipped unnessary info )
-------

<class name="A" table="T_A">
  <ID name="id" column="ID_A" />
  ...
  <joined-subclass name="AA" table="T_AA">
    ...
  </joined-subclass

  <joined-subclass name="BA" table="T_BA">
    ...
  </joined-subclass

  <joined-subclass name="CA" table="T_CA">
     ...
     <discriminator column="TYPE_CA">
     <subclass name="ACA" discriminator-value="ACA" >
       ...
     </subclass>
     <subclass name="BCA" discriminator-value="BCA" >
       ...
     </subclass>
  </joined-subclass