Newsreaders all need some way to quickly grab data from
a range of articles.  trn, tin, nn, and others each developed
their own database format, and their own extensions to the NNTP
protocol for clients to read the database.  Then, Geoff Collyer
invented NOV, the database to end all other databases.

Rather than support a different database format for each newsreader,
INN supports Geoff Collyer's news overview database, NOV.  INN includes
everything you need to create/maintain/expire NOV's .overview files.
You only need Geoff's distribution (available via FTP on ftp.std.com
src/news/nov.dist.tar.Z) if you want to see how he implements things,
or to get his client library (useful when building some newsreaders).

It is very easy to configure INN to use NOV.  Read Part 4/9 of
this faq: Subject: Cookbook example of setting up NOV ("overchan")
NB: The NOV code in INN 1.3 is buggy.  Use 1.4 or higher.

The xover command is used for querying the NOV database.  The xover
command is very smart in that if the article has been canceled, the
data isn't given out.  If the article is so new that it's data isn't in
the NOV database, nnrpd opens the article and digs out the data.  xhrd
and xpat make every effort to use NOV data before they dig the data out
of the actual articles, thus making them considerably faster than other
implementations.  The "xoverview" command does not exist.  If your
server supports this command you need to upgrade.

What about TRN's xthread command?

The xthread command has code but it is not supported; look at
$inn/nnrpd/nnrpd.h.  This code will probably vanish after 1.4.

What about TIN's many commands?

Tin commands are not supported.  However, other people have
added TIN support.  See the next section.

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