And for your question about the meaning of "mapped-name": I think this is the JNDI name of the JDBC datasource (and thus the same as declared in your oracle-ds.xml file) + prefix "jdbc/...".
The "res-ref-name" is the name of the entry in your Environment Naming Context (needed only for programmatic JNDI lookups), it is NOT the name of the datasource in JNDI.
Hope this helps
Wolfgang