"output file name must be specified if database not mounted"
*Cause: A datafile restore specified no target file name, but the
database is not mounted. The database must be mounted when no
target file name is specified, so that the target file name
can be obtained from the control file.
*Action: The restore conversation remains active. If you wish to restore
datafiles without their target file names, then mount the database
before continuing. Otherwise, a target file name must be specified
on all datafile restoration calls.