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

Jim Whitehead wrote:
>>  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.

Correct. For instance, subversion could use it's global version counter 
as Etag.

>>   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.

That's correct, but I really have a hard time understanding why anybody 
would *think* that ETags can be used that way. If they could, we 
wouldn't need DAV:resource-id...

 > ...

Best regards, Julian

<green/>bytes GmbH -- -- tel:+492512807760

Received on Wednesday, 19 January 2005 01:15:03 UTC