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The Overview Database

first of all, nov, or the netnews overview database, the overview
database are all the same thing.  it is a database of a couple of the
most popular headers.  it was designed by Geoff Collyer as a standard
way of quickly getting header information, so that it could be used by
threading newsreaders.  it is organized, one file per newsgroup, ala

	/usr/spool/news/<group>/.overview

the file contains a one-line summary, in order, of every article in
that group.  the fields are separated by tabs and any tabs or newlines
in the original headers are replaced by spaces.  the fields in order
are article number (filename), subject, author, date, message-id,
references, byte count, line count.  other optional locally arranged
headers maybe tacked on the end, but they should be proceded by the
header keyword.

this is how Geoff wrote this for Cnews, INN allows additional
flexibility by allowing the database to be in a different directory
hierarchy than /usr/spool/news, and you can call the .overview file
something else, like overview--without the dot.

ie
 artno<T>Subject<T>From<T>Date<T>Mess-Id<T>References<T>Bytes<T>Lines

the format is very straight forward, and is not prethreaded, the
reason behind this being that threading can be done reasonably quickly
on the client, and rather than going for a particular kind of
threading, just make the data *quickly* available and let the client
decide how to order it.

The XOVER Command

the XOVER command is an extension to NNTP to allow access to the
overview database.  the syntax of the command is basically:

        XOVER range
        range := artno | artno '-' artno
        artno := [0-9]+

one has to have done a 'GROUP' command earlier to establish a current
group.  if successful, it returns a code '224', the data [as described
above], then a '\r\n.\r\n' to let you know it's done.


Support

the overview database is supported in Cnews by Geoff's nov
distribution available for ftp at world.std.com
/src/news/nov.dist.tar.Z.  in the future, it will probably be included
in future versions of Cnews.  this package also contains some wiz bang
threading routines for clients, plus the official newsoverview.5 man
page!

there are patches to the reference implementaion of NNTP, to add the
XOVER command.  hopefully stan barber will include them in his next
release of the reference implementaion.

InterNet News 1.3 (released real soon now) will support both the
overview database and the XOVER command.

as far as newsreaders go, new versions of trn and tin which are both
in beta test support the overview database and the XOVER command.
i've posted patches for GNUS, and Felix Lee promises to post even
better ones.  

hope this explains it and if i got anything wrong, please let me know.

rob
--
			  william robertson
			rob@agate.berkeley.edu

     "when i was your age, i walked 10 miles to school, unarmed."