class ServantBase {
public:

    virtual ~ServantBase ();

    virtual InterfaceDef_ptr _get_interface () throw (SystemException);
    virtual Boolean _is_a (const char *logical_type_id) throw (SystemException);
    virtual Boolean _non_existent () throw (SystemException);

    virtual void _add_ref ();
    virtual void _remove_ref ();

    ...
}