Triggers, Stored Procedures to Aggregate table ?

Hi,

Very new to the Triggers and Sprocs.

I have few tables which stores raw data on minute basis. I want to aggregate
this data into another table to store every hour worth of data. And from there
on - from this hourly Aggregated table, want to store into another Aggregate
Table for a day's worth of data.

You got the direction I am going with this.. :-).... Hourly, Daily, Weekly
aggregated data into their respective tables.

I could write some Java code to run periodically on these tables to transform
them into Aggregate tables but that would have the overhead (Network, Disk
I/O). I am wondering if there is any easy way to be able to write something at
the Postgres level, where some Trigger will call some Stored Procedure on a
particular table which will do the Aggregate (min, max, avg) and store that into
a new table.

Any pointers or suggestions or examples would be highly appreciated !

Thanks!
Arvind