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Re: 'Age' for webpages

From: Aryeh Gregor <Simetrical+w3c@gmail.com>
Date: Tue, 8 Jun 2010 18:20:29 -0400
Message-ID: <AANLkTim1RKsnI0WBFxs-KqcZOG11baNft-tREuJrQmIt@mail.gmail.com>
To: Julian Reschke <julian.reschke@gmx.de>
Cc: Merin Tresa Willy <merintwilly@gmail.com>, David Woolley <forums@david-woolley.me.uk>, asseerao@gmail.com, adam.delvecchio@go-techo.com, www-html@w3.org
On Tue, Jun 8, 2010 at 1:09 AM, Julian Reschke <julian.reschke@gmx.de> wrote:
> Why does "changes every few minutes" make it meaningless?

Strictly speaking, it doesn't.  However, there are plenty of pages
that include so much dynamic content that any utility in providing a
Last-Modified header would be outweighed by the effort you'd have to
go through to figure out which piece was actually the most recent.
For instance, look at this page:


It includes the current time, the last post in each top-level forum,
the post counts for all forums and for the board as a whole, and a
list of users online.  You'd have to do a pretty large amount of
careful work to figure out which of those actually changed most
recently, and you'd have to take into account all other possible
options that the admins might enable.  If you look at
<http://www.phpbb.com/community/viewforum.php?f=46>, it even includes
the number of *views* for each thread, and the software probably
doesn't even bother storing when the last view was, so computing
Last-Modified correctly is actually impossible.

And after all this you end up with a Last-Modified header that will be
the beginning of the current minute at the earliest.  That's not very
useful for any client application that I can think of.  So clearly not
worth the effort, contrary to the earlier suggestion that
competently-authored dynamic content will have Last-Modified.

(Of course, Last-Modified is useful for *some* dynamic content, just
not all.  MediaWiki serves it on article pages, for instance, but not
for most special pages.)
Received on Tuesday, 8 June 2010 22:21:02 UTC

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