It's a common problem: database applications cannot access relational databases because firewalls block the necessary ports. A workaround for this limitation is to implement Web Services for the internal business logic API. The drawback of this is that you have to adapt your design or create additional code. Moreover your application now always communicates over a slower API even if your application is deployed in an intranet environment. Therefore it is no good practice to use Web Services only for the sole reason of tunnelling the internal messaging bus through firewalls.
The Universal SQL Gateway Project addresses this issue. The Universal SQL Gateway tunnels SQL requests through firewalls over HTTP by implementing a special JDBC driver. The Universal SQL Gateway Project mission is to provides secure database access by acting as a firewall component commonly referred to as Application Gateway. You don't have to adapt your design for this and even can use it in existing database applications. If your application has to cope with a firewall between the client and the database you use the Universal SQL Gateway JDBC driver. If your application operates behind the firewall you simply switch back to your native driver. The Universal SQL Gateway is database and platform independent. Besides the JDBC driver it also offers an XML Interface, which makes it possible to implement drivers for other languages, too.