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(at)unl(dot)edu(dot)ar
Programador, Administrador | Centro de Telematica
Universidad Nacional
del Litoral
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