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Path: utzoo!mnetor!uunet!seismo!rochester!ritcv!moscom!jgp
From: jgp@moscom.UUCP (Jim Prescott)
Newsgroups: news.admin
Subject: A possible solution to the Expires: problem
Message-ID: <1026@moscom.UUCP>
Date: Wed, 29-Jul-87 22:26:39 EDT
Article-I.D.: moscom.1026
Posted: Wed Jul 29 22:26:39 1987
Date-Received: Sat, 1-Aug-87 02:07:07 EDT
Reply-To: jgp@moscom.UUCP (Jim Prescott)
Organization: MOSCOM Corp, E. Rochester, NY
Lines: 47
Summary: Invent a Supersedes: header line

It occurs to me that OtherRealms is not the only place where it is
desirable to try and insure that an old article stays around until
a new one shows up.  Things like arbitron results, newuser documents
and uucp maps all have a lifespan that ends when the next posting of
the info is received.  What makes OtherRealms look different is that
the length of time between postings necessitates very long expiration
times.  With OtherRealms the idea is to keep at least one version
around, with groups like newusers the idea is to keep at most one
version (the most current).

How about a new header line of the form:
	Supersedes: message_id [message_id ...]
When an article comes in with a Supersedes line news posts it normally
and then does a cancel on the message_ids indicated.  As an example,
a weekly posting could be given a one month expiration date but would
carry a Supersedes line for the previous 4 weeks messages.  Even if a
site misses one or two postings they will always have only the most
recently received copy available.

This is similar to just having the people who make the periodic postings
send a normal cancel for the old copies but has the advantage that the
cancel and the replacement article always arrive together.  It is also
more efficient since in the above example the poster would need to send
4 cancel messages every week to get the same protection against articles
being lost.

Some problems I can see with this are:
	- It is more bookkeeping to track the old message_ids.  Since
	most of the periodic postings are probably largely automated
	this shouldn't be too bad.
	- It might lead to longer expiration times being used with
	the intent that the article would be superseded before expiring
	anyway.  This will annoy the people whose software doesn't
	understand the new header line.
Some benefits are:
	- Savings of disk space since old messages will be removed as
	soon as they become obsolete instead of waiting for expire.
	- One of the groups this would help would be newusers, anything
	that cuts down the volume there without losing info will make
	it more likely that people will consider reading the stuff in
	the first place.
	- It becomes easier to make sure that even sites with flaky
	newsfeeds always have a recent copy of your article.

Any comments?
-- 
Jim Prescott	seismo!rochester!moscom!jgp or moscom!jgp@cs.rochester.edu