how to write the inverns dns file

[David Portabella]

in named.conf, I have:
--------
zone "." {type hint; file "db.cache"; };
zone "example.com" {type master; file "db.example.com"; };
zone "209.17.22.7.IN-ADDR.ARPA" {type master; file "db.209.17.22.7"; };

------
in db.example.conf, I have:
----------
$TTL 86400
example.com. 43200 IN SOA 192.168.1.1. david.example.es. (193149117 21600
10800 1728000 43200)
example.com. IN NS 209.17.22.7.
example.com. IN RP davidp.otherexample.com. David.example.com.
David.example.com. IN TXT #David, NIC handle: DAVID127#
example.com. IN A 209.17.22.7
www.example.com   IN CNAME example.com.
--------

can you give the minium example of "db.209.17.22.7" enough to work?

Thank you very much!
ps: example.com and that IP are only examples.