groups in postgres

I building an application that will load data on a database by lots of 
people. So I thought about putting them in a group and giving priviledges to 
the group.

The problem is the the information on the main table is related with fields 
of other tables, and depending on how it's related, I want some users to be 
able to modify the data and I don't want those users to insert new data if 
the relation is right for them.

Am I clear up to know?

Now, how can I do this? Is it posible manipulating groups? Or do I have to 
play with triggers.

Saludos... :-)

-- 
El mejor sistema operativo es aquel que te da de comer.
Cuida tu dieta.
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Martin Marques                  |        mmarques@unl.edu.ar
Programador, Administrador      |       Centro de Telematica                      Universidad Nacional                           del Litoral
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