Doing sth. like oracles "connect by"

What is the most effective and elegant way to substitute the connect by
clause from oracle in postgresql?

Explanation of connect by:

with "connect by" in oracle it is possible to formulate queries returning
whole hierarchies.

Example:

TablePersonal

ID IdOfChef Name PositionLevel
1 2 Karlchen 2
2 3 Melanie 3
3 4 Katja 4
4 5 Simon 5
5 NULL Miriam 6

select * from TablePersonal start with id=1 connect by prev.idofchef=id
where PositionLevel < 6

selects the total hierarchie above karlchen ... up to Simon.

select * from TablePersonal start with id=3 connect by prev.id=idofchef

gets Katja and all her downlinks (Katja, Melanie, Karlchen)

the ideas I can think are:
a) join with a a limited number of hierarchie-levels and perform well.
b) program a function "is_downlink_of(id1, id2) returns boolean" - and
check this function for every row in the table
c) (the same as c but with "is_uplink_of(id1,id2)")

Who has an idea which does not have the high processing costs of b and c and
not the limitation of a)

Thanks for your thinking

Harald