a trigger for time

Hello to everyone,
I've got a set of tables where I need to store both the inserting and updating 
time of a tuple. These columns are of coure two "time" columns. I'd like to 
build a trigger (before) so that the time can be set up rightly when my 
programs perform an insert or an update, but I cannot understand how to do 
it. Does anybody know where I can find some example (or better is there 
anybody who can send me an example)?

Thanks,
Luca

-- 
Luca Ferrari,
fluca1978@xxxxxxxxxxx

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