RMAN experiemnt demo: recover of missing a datafile

RMAN> alter database open;
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of alter db command at 11/07/2012 13:18:18
ORA-01157: cannot identify/lock data file 12 - see DBWR trace file

RMAN> list failure;
List of Database Failures
=========================
Failure ID Priority Status    Time Detected Summary
---------- -------- --------- ------------- -------
515922     HIGH     OPEN      07-NOV-12     One or more non-system datafiles are missing

RMAN> advise failure;
....
Automated Repair Options
========================
Option Repair Description
------ ------------------
1      Restore and recover datafile 12 
  Strategy: The repair includes complete media recovery with no data loss
...
#repair  failure;
RMAN> restore datafile 12;
RMAN> recover datafile 12;
RMAN> alter database open;