W3C home > Mailing lists > Public > ietf-http-wg-old@w3.org > January to April 1995

"Expires" again...

From: Paul Burchard <burchard@horizon.math.utah.edu>
Date: Thu, 12 Jan 95 13:23:14 -0700
Message-Id: <9501122023.AA03067@horizon.math.utah.edu>
To: cwilson@spry.com, allocca@openmarket.com
Cc: Multiple recipients of list <www-talk@www0.cern.ch>, M.J.Cox@bradford.ac.uk, fielding@avron.ICS.UCI.EDU, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com, "Daniel W. Connolly" <connolly@hal.com>
Chris Wilson <cwilson@spry.com> writes:
> Bill Allocca <allocca@OpenMarket.com> writes:
> >Is there any way in HTTP for a Server to automatically update a page
> >without requiring the user of the client to click on anything?
>
> Because of the other problems that you noted (namely,
> that clients are not required to automatically reload a
> document when it passes the Expired time- in fact, it
> would be detrimental to do so),
>
> >there are cases where a page is valid only once --
> >they expire immediately and the client shouldn't get
> >them again.

The current HTTP draft spec *does* specifically
interpret "Expires:" as a client directive to
automatically reload the data at that time -- i.e. expiry
interpreted as "data expiry".

However, along with Dan Connolly, and others that Bill
Allocca mentions, I also originally interpreted
Expires as a server guarantee to deliver constant data up
to that time -- i.e. expiry interpreted as "URL expiry".

My own example of "URL expiry" without "data expiry" was
that of custom inline images inside FORM-generated
documents, which get deleted from the server
immediately upon retrieval.  According to the HTTP draft
spec, I should not tell the client to "expire" these
images.

> I would propose an "Expires-Auto-Update:" field - with a
> value of "yes" or "no", default "no" in case of the header
> line not appearing - which would force the client to
> automatically update the page.

Since, "data expiry" and "URL expiry" are independent
issues, as the examples have shown, it seems like we
really need two independent time headers, say
"Data-Expires:" and "URI-Expires:".

According to the current HTTP spec draft, "Expires:" means
"Data-Expires:", and this does seem like the more generally
useful one.

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Paul Burchard	<burchard@math.utah.edu>
``I'm still learning how to count backwards from infinity...''
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Received on Thursday, 12 January 1995 12:48:43 EST

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