[edoceo]

Oh, I've done this. The 4DBs are for forward-origination, servicing and reverse origination, servicing.

We had a prime app, a fifth DB driving it. It had scripts to pull rates and a UI to adjust. Logs all changes.

These rates are pulled by the other systems (eg the AS400 pulled over FTP). Additional internal apps could query over SMB and HTTP.

The prime updated slowly and each of the services would poll it very frequently (4m) + on-demand when needed