[NNTP] Article references

[Clive D.W. Feather]

A recent thread in news.software.nntp asks whether the same article can
have two different article numbers in the same newsgroup. The requirements
on arrival times means there can't be any other valid number between them,
but I don't see it actually outlawed by our text.

I propose modifying section 6 as follows:

   News reading clients have available a variety of mechanisms to
   retrieve articles via NNTP.  The news articles are stored and indexed
   using three types of keys.  One key is the message-id of an article.
   Another key is composed of the newsgroup name and the article number
   within that newsgroup.  That key MUST be unique to a particular
   server (there will be only one article with that number within a
   particular newsgroup), but is not required to be globally unique.
   Additionally, because the same article can be cross-posted to
   multiple newsgroups, there may be multiple keys that point to the
-  same article on the same server.  The final key is the arrival
+  same article on the same server; however, these keys MUST each refer
+  to a different newsgroup.  The final key is the arrival
   timestamp, giving the time that the article arrived at the server.

Any objections?

-- 
Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:    +44 20 8495 6138
Internet Expert     | Home:  <clive at davros.org>  | Fax:    +44 870 051 9937
Demon Internet      | WWW: http://www.davros.org | Mobile: +44 7973 377646
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