Oracle Database Discussions

Hallo!I am an Oracle 10g newbie who is studying for the Administration OCA exam.

I was trying to place the database in archive log mode and I had tried to come up with the archive log file name.

I was forced to restart the instance and from sqlplus I have tried to start the instance each time via the startup commands :startup force, startup nomount; startup mount; startup open but the ORA 19905 error still appears as below

SQL> conn /as sysdba;
Connected to an idle instance.
SQL> startup force;
ORA-19905: log_archive_format must contain %s, %t and %r

How do I resolve or bypass this.Also using an example,give me the best format for naming an archive log file which adheres to the archive log format.

Thanks.