Undirected graph in Oracle SQL -

i'm trying represent undirected graph in oracle sql, example, have stations graph:

create table station (    station_id integer not null );  create table station_link (   from_station integer not null,   to_station integer not null ); 

this directed graph, have no idea, how make undirected.

point: i need vertices, have path current vertex , information level (how many vertices on path).

for directed graph pretty easy:

select sl.to_station, level   station_link sl start sl.from_station = :curvertex connect nocycle prior sl.to_station = sl.from_station 

but one-way verticies.

question: do problem have solution, except adding additional links (2 -> 1 1 -> 2)?

there sql fiddle tests: http://sqlfiddle.com/#!4/6c09e/24

for "fast win" can use structure "as is", every edge shold have 2 records in station_link table.

if want "not_so_fast_but_without_doble_edge_records_please win", can use weirdo-trick:

select   x.to_station,   x.lvl (         select sl.to_station, level lvl           station_link sl         start sl.from_station = :curvertex          connect nocycle prior sl.to_station = sl.from_station          union         select sl.from_station to_station , level lvl           station_link sl         start sl.to_station = :curvertex          connect nocycle prior sl.from_station = sl.to_station ) x 

it work. actually, combines 2 traversal directions.

but if i'll want implement serious algorithms on graphs in plsql, sdo_geometry data type , oracle spatial , graphs datasheets.