jdbcPersistenceAdapter & dataDirectory

Is
http://activemq.apache.org/maven/apidocs/org/apache/activemq/store/jdbc/JDBCPersistenceAdapter.html#setDirectory(java.io.File)
not redundant?

Looking at http://activemq.apache.org/jdbc-master-slave.html the example
configures a JDBC persistence adapter with both a data directory and a data
source which is not expected.

James