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RE: ETags? (was: WG Last call for BIND)

From: Jim Whitehead <ejw@soe.ucsc.edu>
Date: Tue, 18 Jan 2005 17:08:00 -0800
Message-Id: <200501190108.j0J189VC025174@services.cse.ucsc.edu>
To: "'Brian Korver'" <briank@xythos.com>, "'WebDAV'" <w3c-dist-auth@w3.org>

 
>   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.

My recollection is that a server might decide to implement Etags as a simple
integer that is updated on every state modification. In this case, all of
the resources on a server would start out with the same Etag value of "1".
In this case, the fact of all Etags being "1" certainly doesn't imply that
all URIs are mapped to the same resource. The fact that all Etags have the
value "1" is still consistence with Etags being defined on resources.

>    Entity Tags and Bindings
> 
>    It might be thought that ETags would be associated with resources,
>    not URIs, and as such two different URIs with identical ETags
>    would imply that the URIs are bindings to the same resource.
>    This is not the case, however.  Section 3.11 of [RFC2616]
>    states that ETags are on URIs, not resources.

So, if we were to put in language, I'd add something like:

Implementors note: Etag values are only required to be unique across all
  versions of a particular resource, not unique across all versions and
  all resources. As a result, two separate resources may have the same
  Etag value, and hence Etag values cannot reliably be used to establish
  the identity of a resource accessible via multiple URIs.

- Jim

PS - How is the quota specification coming along?
 
Received on Wednesday, 19 January 2005 01:08:11 GMT

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