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Re: Variant IDs

From: Larry Masinter <masinter@parc.xerox.com>
Date: Tue, 12 Mar 1996 00:30:45 PST
To: paulle@microsoft.com
Cc: fielding@avron.ICS.UCI.EDU, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <96Mar12.003053pst.2733@golden.parc.xerox.com>
> Good point. The one thing that I think still differs is that lost is 
> the ability for the cache to know that several things with the same URI 
> are variants of one another, as opposed to just a single instance that 
> has changed over time. With IF-ID/Unless-ID/Content-ID:
> 	Client			Server
> 	GET /foo.txt HTTP/1.1
> 				HTTP/1.0 200 OK
> 				Content-ID: "asdasfa"
> 	GET /foo.txt HTTP/1.1
> 				HTTP/1.0 200 OK
> 				Content-ID: "xxxxx"

> How does the cache know if the two "foo.txt" are variants of one 
> another, or if the one-and-only "foo.txt" has changed?

The 'last-modified' of a negotiable resource should be the
maximum of the last-modified of all presentations. If the two
responses have the same last-modified, the two contents are variants
(and need a Vary header); if the second has a different last-modified,
then it marks all the other variants than the one being served as
stale.
Received on Tuesday, 12 March 1996 00:34:49 EST

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