START --+-> DEFAULT TRANSACTION --------------------------+-->
          +-> TRANSACTION -+------------------------------+-+
                           +--+-+-> transaction-mode -+-+-+
                              | +-> isolation-level --+ |
                              +---------- , <-----------+

  transaction-mode =

  --+-> READ ONLY ---+-->
    +-> READ WRITE --+

  isolation-level =

  ---> ISOLATION LEVEL --+-> READ COMMITTED ----+-->
                         +-> REPEATABLE READ ---+
                         +-> SERIALIZABLE ------+