How to mirror remote sites?

Let's say we have a main location wich have a couple of remote sites. We want to ensure that the main location gets updated by the remote sites at least once a day. We obviously don't want to export the whole database or even specific tables (too much data), and the actual Oracle tools to do such things are not very ellaborated. We can't use SQL*Net (phone lines are too slow, and the application does not require it).

Each remote site access only it's own data, but the main location can read any remote site information.

I was wondering if it would be possible to do something with log files... But the information (specifically, the file format) is scarce.

Any suggestion or similar experience are welcome!

--
 Stephane Hamel (SHamel_at_Mais.Hydro.Qc.Ca) | AutoControl Inc.
 Senior Programmer-Analyst                | Montreal, Quebec, Canada