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Re: Issue 535 - viewing state for things removed from cache

From: Charles McCathieNevile <charles@w3.org>
Date: Thu, 11 Apr 2002 08:36:26 -0400 (EDT)
To: "Ian B. Jacobs" <ij@w3.org>
cc: WAI UA group <w3c-wai-ua@w3.org>
Message-ID: <Pine.LNX.4.30.0204110824420.11798-100000@tux.w3.org>
There is no necessity for a user agent to implement a cache in order to
implement a history mechanism.

In practical terms I suspect that requiring state information for cached
content might be appropriate.

Why I suspect, instead of agree: For systems that do not implement a cache
(or have it as part of a chained/proxy based system, like WAP-style browsers,
or "network computers"), it might be difficult to identify this. So I think
there are cases where a history mechanism should "pay this tax" even though
it doesn't have the cache.

Does this help lead to a resolution?


On Wed, 10 Apr 2002, Ian B. Jacobs wrote:

  What about if the user configures the user agent to not cache more
  than, say 1M of data? If the user has visited a page recently, but
  the page has been removed from the cache due to the user's memory
  preferences, are you suggesting that the user agent track state
  information that is is no longer caching? Even if the answer to that
  question is "yes", that can't be done infinitely either. So at some
  point, the user may have recently visited a page and the user agent
  may not have state information stored anymore. It is for this case
  that the notes (not really a formal proposal yet) suggest that the
  UA is not required to restore state.

  Note that this checkpoint does not require a history mechanism.
  It starts:

    "For user agents that implement a viewport history mechanism..."

  [One developer referred to a required history mechanism as a
    "history tax."]

  This checkpoint requires UAs to store state information, but it
  does not require user agents to store an infinite amount of
  state information. I don't think that we should tell user agent
  developers how to implement cache mechanisms, or how much to
  cache (though user-configurable seems like a good idea). In this
  light, it makes sense to me to say "When info is no longer in the
  cache (that is implemented by definition for a history mechanism,
  but UAAG 1.0 does not require a minimal size), state information
  need not be saved."

    - Ian

Charles McCathieNevile    http://www.w3.org/People/Charles  phone: +61 409 134 136
W3C Web Accessibility Initiative     http://www.w3.org/WAI  fax: +33 4 92 38 78 22
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Received on Thursday, 11 April 2002 08:36:27 UTC

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