Loading exchange rates from flat files

We need to load at least two sets of exchange rates from flat files, and then use these exchange rates in the queries using currency conversion keys.

Where can I find information on the format of these files? I suppose the file needs information on both the 'from' currency, the 'to' currency, exchange rate and date/period, but I have so far not succeeded in creating a working test file.

We are using BW 3.5.