About parameter file

Hi Vital,,,good morning 
here what my question was?
. At one time you lost parameter file accidentally and you don't have any 
backup. How you will recreate a new parameter file with the parameters set to 
previous values.
Can u plz tell me ...How we can proceed in this situation?

You don't want to loose your SPFILE.  You should always use SPFILE for 
production -- PFILE should only be used temporary for clones/moves etc..

When you use SPFILE and RMAN backups (the ONLY right way) you should also 
enable RMAN control and spfile autobackup using this command:

CONFIGURE CONTROLFILE AUTOBACKUP ON;

This way everytime you take RMAN backup it will automatically include SPFILE 
and CONTROL file in the backup set.  You'll never loose it this way.

If you inherit a bunch of COLD datafiles and no SPFILE to go with them then 
there's nothing you can do to get the original SPFILE values back.  Instead you 
just bring up the database with default PFILE and go from there ... trial and 
error kind of thing -- not a good scenario to be in.