Newsgroups: news.software.b
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: How about a 'Replaces' mechanism in addition to supersedes?
Message-ID: <1989Sep21.204025.11748@utzoo.uucp>
Organization: U of Toronto Zoology
References: <17596@looking.on.ca>
Date: Thu, 21 Sep 89 20:40:25 GMT

In article <17596@looking.on.ca> brad@looking.on.ca (Brad Templeton) writes:
>2) Replacement articles move out with the *same* message-id, but a later
>   date of posting.  If inews sees an article come in with a duplicate
>   message id, instead of throwing it away, it checks the date from the
>   history file ...

Unfortunately, in the standard software (both B and C), the date in the
history file is arrival date, not posting date.  This will be difficult
to change; things like NNTP know about it and rely on it.  And having to
dig through the article to decide whether a same-message-id article is
a duplicate or not will be a massive headache -- it will slow news
processing badly, and on NNTP it may not be practical at all.  Many things
assume that message-IDs really are unique identifiers (which is what they
are supposed to be according to the RFCs) and that the message-ID<->contents
relationship does not change.  I think this had better be taken as a clear
requirement.

I don't think the forgery/fraud aspects of this are much worse than we
have now with cancellations and such.

There is a general problem with what the history-file entry for these
things looks like.  For things like duplicate checking and loop breaking,
it is very important that new versions get their own history-file lines.
But if they have distinct message-IDs, do they show up as regular entries
with the same filename(s) as older versions?  There are problems both ways.
For example, expire (any version) is not prepared to cope with the notion
that there might be more than one entry for an article -- it thinks that
when the oldest entry expires, it is okay to remove the file.  You really
have to go back and rewrite the original entry, which is a major hassle.

Appealing though "Replaces" sounds, the complications with things like
the history file strike me as a strong indication that the mechanisms
are being pushed beyond their practical limits.  I suspect that a better
approach is the combination of Supersedes (it is probably easier to get
universal adoption of Supersedes than universal adoption of something
new and strange) plus changes in the news reader(s).
-- 
"Where is D.D. Harriman now,   |     Henry Spencer at U of Toronto Zoology
when we really *need* him?"    | uunet!attcan!utzoo!henry henry@zoo.toronto.edu