Data access from Xpages is a great feature. This allows so many different kinds of data source to be brought into your application. So is there more than one way to do this. Well yes there is. Odbc drivers have been used for 20 odd years to provide a means of linking to other data. DECS would normally be used at the server level to get data connected. However there is something else which will provide readonly access to data in a way which may be very useful to you.
The Domino JDBC Access (a.k.a. DomSQL) exposes Domino data as relational tables and provides easy access to the tables using a JDBC driver. JDBC stands for Java Database Connectivity. It is a set of technologies that are part of the standard Java Runtime environment, used to connect to relational databases.
Domsql is an OpenNTF project and can be found here
DominoJDBCAccess (2) is a pdf document produced by Nicklas Heidloff as part of the project – and it really gives a flavour of the kinds of things you can do – with this and related products.