triggers

Dear list,
Just starting out with postgresql, I've got a 18 table db listing info
on organisations and on the main organisation table I've got an
update column (timestamp), to keep a record of the last time
information was updated for each organisation.
Obviously I can do it on the client app, but I think table /row
triggers might be a better solution
is there a straight forward way of, on updating any of the
organisation tables I can update the update column for that
organisation?

eg On update orgsubtable wher orgId = X
trigger update orgMainTable.timestamp Values(now()) where
orgId = X

TIA

Paul Butler

Sorry about the previous post