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Re: ISSUE VARY: Proposed wording

From: Henrik Frystyk Nielsen <frystyk@w3.org>
Date: Tue, 08 Jul 1997 14:31:59 -0400
Message-Id: <>
To: Koen Holtman <koen@win.tue.nl>
Cc: http-wg@cuckoo.hpl.hp.com
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/3689
At 10:04 PM 7/7/97 +0200, Koen Holtman wrote:

>>An HTTP/1.1 server MUST include a Vary header field with any cachable
>                                 ^^^
> why did you leave out `an appropriate'?  I think that leaving this
> out makes the text worse.  `an appropriate' signals that is the
> responsibility of server to ensure that the client does the right
> thing based on the vary header field contents.

To me, "appropriate" doesn't make a lot of sense in a spec - it is a
nothing but a fill word. The whole spec is about describing the "right
thing" or what's appropriate compared to what is "unappropriate", "bogus"
or "brain dead".

>>response that is subject to server-driven negotiation. Doing so allows a
>>cache to properly interpret future requests on that resource and informs
>>the user agent about the presence of negotiation on that resource. A server
>>SHOULD include a Vary header field with a non-cachable response that is
>>subject to server-driven negotiation, since this might provide the user
>>agent with useful information about the dimensions over which the response
>>vary at the time of the response.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Again, I liked the old text better.  The addition of `at the time of the
> response' only begs questions which need not be answered.

There is an important note to this in that it points out how the vary
header allows a cache to handle _future_ requests based on what a server
knows _at the time_ of the response. This was one of the things that was
confusing in the current wording in the spec.

The time of the response is well-defined - it's the time at which the
message was originated and which may be put into a Date header. This is
described in section 14.19.


Henrik Frystyk Nielsen, <frystyk@w3.org>
World Wide Web Consortium
Received on Tuesday, 8 July 1997 11:35:58 UTC

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