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