ODBC Pathway is a set of products which are based around an XML to ODBC bridge server. This concept is based on an old open-source project called ODBC Socket Server, but with an extended syntax (while retaining backwards compatibility for older clients). The server (which now takes two forms as a Window service and a stand-alone Tray Application) has been completely re-written using the .NET Framework Version 1.1.
Put simply, it allows your application, sitting anywhere on the internet, to send an XML request to the ODBC Pathway Server which will perform the requested database operation, and return the results. Although the intention of the legacy product was originally that the database operation should be a single query, we now permit a wide variety of operations, and even multiple operations in a single request. For more details, see the Protocol page which details how the system works.
You could use Unix ODBC, get the appropriate drivers for the target database, then open all the required ports on your firewall. But each of these steps is both complex and ties you to a specific platform/technology. The intention of ODBC Pathway is to open up database access and free it from the constraints of single vendor limitations.
By using ODBC Pathway you need only open one TCP port (9628) on your firewall and you need only use one client API (the ODBC Client Protocol). As the protocol is a simple TCP connection, you only need to open the connection OUT through your client firewall (Many database protocols will require you to open a return path as well, which could be a security risk).