Oracle7+NW3.12:Rebuild after crash?

I'm posting this for a friend.

He has a Oracle 7 server with NetWare 3.12 and it seems that the database is crashed (he don't know exactly what had happend). All files in the RDBS-directory are shortened to length 0 which meens that the system-table-space is lost. The other table-spaces are ok (in another directory).

He has tried to build a new system-table-space exact like the old one and to replace the data-table-space by the old, but Oracle said "That's not mine!".

1. Has anybody an idea what had happened and how to avoid it in future?
2. Is there a way to get the data from the data-table-space back (like this one tryed, but with a trick or so)?

!!! Please reply by e-mail to: Huetter_at_Informatik.TU-Muenchen.DE !!!

Many Thanx in advance,

Alex