SQL Syntax problem

Hello.

I've got a problem in porting the following select statement from Oracle to 
Postgres, because of the characters after "b.bet_id" and "f.ask_id" in the 
where clause: (+)
I don't know what these characters mean and how I can transform these into 
PostgreSql Syntax.


select        ...
from         auswahlkatalog k, anspruchkorrektur a, beteiligter b, v_betkorr f
where           k.awk_id = a.awk_id and b.bet_id(+) = a.bet_idemp    and a.ask_id = f.ask_id(+);


Hoping for help.
Doris