PROCEDURE button_proc IS
  action varchar(80);

  -- hide a button (for ENTER_-, EXECUTE_- or CANCEL_QUERY)
  PROCEDURE show_off(item_name VARCHAR2) IS
  BEGIN
    IF NOT Id_Null(Find_Item(item_name)) THEN
      Set_Item_Property(item_name, ENABLED,PROPERTY_FALSE);
    END IF;
  END;

  -- try to show a button (for the two query-states. If there is no button to show,
  -- return FALSE to the calling procedure.
  FUNCTION show_on(item_name VARCHAR2) RETURN BOOLEAN IS
  BEGIN
    IF NOT Id_Null(Find_Item(item_name)) THEN
	    Set_Item_Property(item_name,DISPLAYED,PROPERTY_TRUE);
      Set_Item_Property(item_name,ENABLED,PROPERTY_TRUE);
      RETURN TRUE;
    ELSE
      RETURN FALSE;
    END IF;
  RETURN NULL; END;

BEGIN    
  action := Get_Item_Property(NAME_IN('SYSTEM.TRIGGER_ITEM'),ITEM_NAME);

  IF action = 'ENTER_QUERY' THEN
    -- only hide the ENTER_QUERY button, if there are EXECUTE_QUERY and (!!) CANCEL_QUERY
    -- buttons. Otherwise an existing EXECUTE_QUERY button will be shown.
    IF show_on('EXECUTE_QUERY') AND show_on('CANCEL_QUERY') THEN
      show_off('ENTER_QUERY');
    END IF;
  END IF;
  IF action IN ('EXIT_FORM', 'EXIT','QUIT') THEN
    action := 'EXIT_FORM';
    IF NAME_IN('SYSTEM.MODE')='ENTER-QUERY' THEN
      Do_Key('EXIT_FORM');
    END IF;
  END IF;
  IF action = 'CANCEL_QUERY' THEN 
    action := 'EXIT_FORM';
  END IF;
 
  Do_Key(action);
 
 IF NAME_IN('SYSTEM.MODE') != 'ENTER-QUERY' THEN
    IF show_on('ENTER_QUERY') THEN
      show_off('EXECUTE_QUERY');
      show_off('CANCEL_QUERY');
    END IF;
  END IF;
  
  
END;

button_proc;
commit;