Oracle: Creating graphviz files showing referential integrity dependencies

with tabs as (
    select
       user own,
       table_name tab
    from
       user_tables
    where
       table_name like '‥'
    and
       table_name not in (‥)
)
select 'digraph {  node [shape = box]' l from dual union all
select
-- lower(substr(tac.tab, 9) || ' -> ' || substr(tap.tab, 9))  l
   lower(       tac.tab     || ' -> ' ||        tap.tab    )  l
from
   tabs                 tap                                                                            join
   dba_constraints      cpk  on tap.own   = cpk.owner and tap.tab             = cpk.table_name         join
   dba_constraints      cfk  on cpk.owner = cfk.owner and cpk.constraint_name = cfk.r_constraint_name  join
   tabs                 tac  on tac.own   = cfk.owner and tac.tab             = cfk.table_name
union all
   select '}' from dual;