will I need nested transactions ?

Hi,

will I need "nested transactions" which - as I read - aren't
implemented, yet ?

I have some objects that rely on each other.
Each has a status like proposal, working, canceled.

table-A <--- table-B <--- table-C <--- table-D

Those are (1, OO) relationships,
A status change above gets cascaded down but not upwards.
If I try to cancel a table-A-record every "lower" record in B, C, D
should be canceled, too, when the transaction is committed.
Since it is possible, that I cancel e.g. a table B object only its
children should get updated but not table-A.

I thought somthing along this to cancel a type B object:

BEGIN
BEGIN
BEGIN
UPDATE table-D
END
if no error UPDATE table-C
END
if no error UPDATE table-B
END

Does this make sense and will it provide the necesary protection ?

BTW the client is Access 2000 via ODBC talking to an PostgreSQL 7.4.2 on
Linux.

Regards
Andreas