Object like pg_class.relkind = 's' or 'c' have on-disk file?

Hi.
I'm writing backup guide and script.

I will look up on-disk-filename should be backuped
in a pg_class, like:
>SELECT oid,relfilenode,relname,relkind FROM pg_class;
it return like:
> 17173 | 17173 | sql_packages | r
> 17182 | 17182 | pg_toast_17178_index | i
> 17180 | 17180 | pg_toast_17178 | t
> 376 | 0 | pg_xactlock | s

I'll include backup set relkind='r' or 'i' or 'S' or 'v' or 't'.
but PostgreSQL 8.0.1 Documentation "41.9. pg_class" say
>c = composite type, s = special

1)relkind = 's' is always have not on-disk file?

2)when exist relkind='s' object except pg_xactlock?
user(administrator) can create it?

3)relkind = 'c' is always have not on-disk file?
(I create TYPE. but no file exist.)
I will only include pg_type relation in backup set. is it OK ?

4)any other advice to backup? :-)

Regards,
--
----------------------------------------
Katsuhiko Okano
k_okano _at_ po.ntts.co.jp
NTT Software Corp. (division "NBRO-PT6")