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i39, was: Moving to editorial: i39 / i51 / i61 / i64 / i94

From: Julian Reschke <julian.reschke@gmx.de>
Date: Thu, 03 Apr 2008 17:23:52 +0200
Message-ID: <47F4F688.10903@gmx.de>
To: Mark Nottingham <mnot@mnot.net>
CC: HTTP Working Group <ietf-http-wg@w3.org>

Mark Nottingham wrote:
> ...
> * i39 - ETag uniqueness
> ...

Looking at 

"Entity tags are used for comparing two or more entities from the same 
requested resource. HTTP/1.1 uses entity tags in the ETag (Section 7.1), 
If-Match (Section 7.2), If-None-Match (Section 7.4), and If-Range 
(Section 6.3 of [Part5]) header fields. The definition of how they are 
used and compared as cache validators is in Section 5. An entity tag 
consists of an opaque quoted string, possibly prefixed by a weakness 

   entity-tag = [ weak ] opaque-tag
   weak       = "W/"
   opaque-tag = quoted-string

A "strong entity tag" MAY be shared by two entities of a resource only 
if they are equivalent by octet equality.

A "weak entity tag," indicated by the "W/" prefix, MAY be shared by two 
entities of a resource only if the entities are equivalent and could be 
substituted for each other with no significant change in semantics. A 
weak entity tag can only be used for weak comparison.

An entity tag MUST be unique across all versions of all entities 
associated with a particular resource. A given entity tag value MAY be 
used for entities obtained by requests on different URIs. The use of the 
same entity tag value in conjunction with entities obtained by requests 
on different URIs does not imply the equivalence of those entities."

...it already seems clear that each entity has it's own etag (expect for 
the special case of weak etags).

Now, what we may want to clarify though is when entities are indeed 
different -- we know that implementors got that wrong with 
Content-Encoding, for instance. That would make it a change to Part 3, I 

- should we try to improve 
(introduction of "Entity"), or

- would it be sufficient to add a warning to the description of 

BR, Julian
Received on Thursday, 3 April 2008 15:24:45 UTC

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