defaults on updates

Hi,
I'm trying to make some sort of function, rule, trigger, or what ever that
would be capable of modifing my table on an update.

Basically, I have 5 fields, one being a PK (SERIAL), 3 with information, and
the last one a timestamp field that will show the last time the register was
modified (tmodif which has a DEFAULT CURRENT_TIMESTAMP).

Now, eveytime someone modifys any, or all of the 3 information fields, I want
the tmodif field of that register to be set to now(). I tried with rules, but
just didn't work (obviously, and not so), even with INSTEAD.

The only way I see of doing it is through a view/rule, but I would leave that
as the last resource.

Any ideas?

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Universidad Nacional
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