> I thought JCA uses JDBC 3.0 and not vice versa!

What I meant here is that core of the driver is implementation of
ManagedConnection, ManagedConnectionFactory, XAResource and
LocalTransaction. They wrap API. All JDBC classes call methods of JCA
implementation. JCA implementation manages all handles, controls
connections and transactions. Therefore we need javax.resource.* and
javax.transaction.* classes.

Also I do not see how JCA can use JDBC 3.0 or JDBC 3.0 can use JCA.
In my opinion these architectures serve different purposes and are
rather complementary (I ignore here CCI interfaces).

Best regards,
Roman Rokytskyy