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Re: ETags, next call, was: Notes on call from today ...

From: Lisa Dusseault <lisa@osafoundation.org>
Date: Tue, 29 Nov 2005 11:49:55 -0800
Message-Id: <d798963775414caa9ac27ac98c41ee4a@osafoundation.org>
Cc: Julian Reschke <julian.reschke@gmx.de>, Geoffrey M Clemm <geoffrey.clemm@us.ibm.com>, WebDav <w3c-dist-auth@w3.org>, Cullen Jennings <fluffy@cisco.com>
To: Wilfredo Sánchez Vega <wsanchez@apple.com>

I hadn't thought that a client could use weak etags at all for 
authoring.  I had started from considering the cases of a JPG or a 
Photoshop file or a Word document.  What does a weak ETag mean for 
those documents?  If I edit a Word document on a WebDAV server and all 
I do is fix a couple inconsistent fonts and a space or two, one might 
think that the weak ETag need not change -- but I would not find the 
system very usable if these changes were lost on a subsequent update.

Lisa

On Nov 29, 2005, at 11:09 AM, Wilfredo Sánchez Vega wrote:

>   Agreed.  If you can only guarantee semantic equivalence and not 
> byte-for-byte equivalence between GETs, you have to must weak etags 
> according to HTTP/1.1.
>
>   A weak etag, as per rfc2616, should sufficient for CalDAV and 
> accurately reflects what's going on in the server if it is generating 
> the iCalendar dynamically.  I don't see why a client can't use that to 
> do sync just fine.  All you care about is whether the etag changes, 
> not whether it's strong or weak, unless you actually need 
> byte-for-byte replication, but I don't know why you would.
>
> 	-wsv
>
>
> On Nov 29, 2005, at 1:24 AM, Julian Reschke wrote:
>
>>>> On the other hand, a server that implements RFC2616/RFC2518 would 
>>>> just use weak ETags, allowing to reformat the content as long the 
>>>> semantics stay the same.
>>> How do weak ETags solve this?  What can a client really rely on if 
>>> the weak ETag is the same, or different?  Do you believe a client 
>>> could rely on weak ETags to do synchronization?  Wouldn't we need 
>>> restrictions on
>>
>> Yes, I would think so.
>>
>>> what changes could be allowed before the weak ETag had to change in 
>>> order to use weak ETags?
>>
>> <http://greenbytes.de/tech/webdav/rfc2616.html#rfc.section.3.11>:
>>
>> "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."
>
Received on Tuesday, 29 November 2005 20:46:56 GMT

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