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Re: Proposal for issue #101 (strong/weak validators).

From: Werner Baumann <werner.baumann@onlinehome.de>
Date: Fri, 14 Nov 2008 23:10:51 +0100
Message-ID: <491DF76B.5090900@onlinehome.de>
To: Yves Lafon <ylafon@w3.org>
CC: ietf-http-wg@w3.org

Yves Lafon wrote:
> 
> Here is a proposed change for issue #101 [1], as the issue is more the 
> definition of "weak validator", being linked to both unreliable 
> identification of changes _and_ the will to signal only significant 
> (read: semantic) changes.
> 
> In paragraph 5 of Part 4 [2], change:
> 
>    [...]
> 
> =>
> 
>    However, there might be cases when a server prefers to change the
>    validator only on semantically significant changes, and not when
>    insignificant aspects of the entity change, or cases where the
>    validator is use does not allow reliable identification of changes.
>    A validator that does not always change when the resource changes
>    is a "weak validator".
> 
>    Entity tags are normally "strong validators", but the protocol
>    provides a mechanism to tag an entity tag as "weak".  One can think
>    of a strong validator as one that changes whenever the bits of
>    an entity changes, while a weak entity tag value changes whenever
>    the meaning of an entity changes. Alternatively, one can think of
>    a strong validator as part of an identifier for a specific entity,
>    while an entity tag used as a weak validator is part of an identifier
>    for a set of semantically equivalent entities.
> 
> Thoughts?
> 
> [1] <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/101>
> [2] 
> <http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-04#section-5>
> 

This does not resolve the contradiction.

"cases where the validator is use does not allow reliable identification 
of changes". In current practise this means changes within the same 
second and there is nothing that restricts the kind of changes that 
might occur.

"a weak entity tag value changes whenever the meaning of an entity 
changes. .. a weak validator is part of an identifier for a set of 
semantically equivalent entities" simply is not true for current practise.

Why do you want to promise or suggest some kind of semantic equivalence 
when arbitrary changes may happen without changing the weak etag?
Just make up your mind and either remove that "semantic equivalence" 
stuff or deprecate current practise.

A specification should not be intentionally ambivalent.

Werner
Received on Friday, 14 November 2008 22:11:45 GMT

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