http://www.oracle.com/technology/obe/11gr2_db_prod/ha/dataguard/dg_broker/dg_broker.htm
http://www.oracle.com/technology/obe/11gr2_db_prod/ha/dataguard/activedg/activedg.htm
http://www.oracle.com/technology/obe/11gr2_db_prod/ha/dataguard/physstby/physstdby.htm