CREATE TABLE t AS SELECT * FROM ( 
SELECT 'A' v1, 'S' relation_type, 'B' v2, 'O' relation_direction, NULL component FROM DUAL UNION ALL 
SELECT 'B', 'S' ,'C',  'O', NULL FROM DUAL UNION ALL 
SELECT 'D', 'S' , 'E',  'O', NULL FROM DUAL UNION ALL 
SELECT 'E', 'S' , 'F',  'T', NULL FROM DUAL UNION ALL 
SELECT 'Y', 'M' , 'Y1', NULL, NULL FROM DUAL UNION ALL 
SELECT 'Y', 'M' , 'Y2', NULL, NULL FROM DUAL UNION ALL 
SELECT 'X', 'S' , 'X1', NULL, 'C' FROM DUAL UNION ALL 
SELECT 'X', 'R' , 'X2', NULL, 'C' FROM DUAL UNION ALL 
SELECT 'X0','S' , 'X1', 'T', 'C' FROM DUAL UNION ALL 
SELECT 'Y0','S' , 'Y1', 'O', NULL FROM DUAL UNION ALL 
SELECT 'Y1','S' , 'Y11', 'O', NULL FROM DUAL UNION ALL 
SELECT 'P','S' , 'Q', 'T', NULL FROM DUAL UNION ALL 
SELECT 'Q','S' , 'R', 'T', NULL FROM DUAL UNION ALL 
SELECT 'R','S' , 'S', 'T', NULL FROM DUAL UNION ALL 
SELECT 'S','S' , 'T', 'T', NULL FROM DUAL UNION ALL 
SELECT 'B', 'S' , 'A',  'O', NULL FROM DUAL) 

with 
  h (parent, child, priority) as ( 
    select  connect_by_root(v1), v2, 1 
    from    t 
    where   connect_by_iscycle = 0 
    start   with v1 = :item 
    connect by nocycle prior relation_type != 'M' 
                   and prior component is null 
                   and v1 = prior v2 
  ) 
, q (parent, child, priority) as ( 
    select v1, :item, 0 
    from   t 
    where  v2 = :item and relation_direction = 'T' 
  ) 
select min(parent) keep (dense_rank first order by priority) over () as parent, child 
from   ( select * from h union all select * from q )