Appendix V:  News overview database

     There are now many  newsreaders  available  that  are  able  to  do
"threading."   This  is  the  ability  to  track a discussion within a
newsgroup by using the References header (or other data), regardless  of
changes  in  headers  like  the Subject line.  Examples of these readers
include nn, trn, and gnus,  and  more  are  becoming  available.   Until
recently, a major problem with these readers is that they all required a
specialized external database that contained the threading data.

     In late 1992, Geoff Collyer <geoff@world.std.com> released the nov,
or  "news  overview,"  package.  This included database tools and, and
client access routines, that let the current threaded newsreaders use  a
common,  textual,  database.   An  overview database typically adds adds
about 7-9% to your storage requirements.  By default, the overview files
are  stored  in  the  spool  directory;  you  can  change this to use an
alternate  tree  that  mirrors  the  spool  hierarchy  by  changing  the
_PATH_OVERVIEWDIR parameter.

     INN includes full support for creating and expiring  news  overview
databases.   To  do  this,  add  an  entry  like  the  following to your
newsfeeds file:

     overview:*:Tc,WO:/path/to/bin/overchan

(Make sure to replace /path/to/bin with the value of your  _PATH_NEWSBIN
parameter.)   Then reload the newsfeeds file or restart your server.  To
create the initial database, run the following command  after  you  have
started overchan:

     expireover -a -s

You will also need to expire the overview data.  The easiest way  to  do
this  is  to  add  the  "expireover" keyword to the cron job that runs
news.daily.

     The nnrpd server includes two  command  extensions  to  access  the
database;  they  are  documented  in the "protocol extensions" part of
doc/nnrpd.8.  INN does not include any client code or  modifications  to
any  newsreaders to use the overview data.  Most maintainers have agreed
to support the overview  database,  including  the  INN  extensions  for
remote  access.   You  can find prototype versions of many readers (work
done by Geoff) on world.std.com in  the  directory  src/news;  look  for
files named reader.dist.tar.Z.