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Re: ldp-ISSUE-10 (Guidance around ETags): Include clarifications and guidance around ETags [Linked Data Platform core]

From: Raúl García Castro <rgarcia@fi.upm.es>
Date: Mon, 04 Feb 2013 09:24:00 +0100
Message-ID: <510F7020.3030906@fi.upm.es>
To: Henry Story <henry.story@bblfish.net>
CC: Steve Battle <steve.battle@sysemia.co.uk>, "Linked Data Platform (LDP) Working Group" <public-ldp-wg@w3.org>
El 03/02/13 19:15, Henry Story escribió:
>
> On 3 Feb 2013, at 18:19, Steve Battle <steve.battle@sysemia.co.uk> wrote:
>
>> ETags (entity tags) can be strongly or weakly validating:
>>
>> A strong ETag match indicates byte-for-byte, syntactic equivalence.
>> A weak ETag match indicates semantic equivalence.
>>
>> For RDF models, semantic equivalence is more important than strong syntactic equivalence. The same RDF content can be serialized in many different, but semantically equivalent ways. This is true even where the same serialization format is used.
>>
>> * I propose that an LDP server should return only _weak_ ETags for LDP Resources and Containers.
>> * For other kind of resources then _strong_ eTags should be used.
>>
>> Weak ETags are prefixed with 'W/'.
>> e.g. "W/1234567890" instead of "1234567890"
>
> Ah thanks for pointing this out. I did not know.
> For others:
>
>     http://tools.ietf.org/html/rfc2616#section-3.11
>
> certainly for graph resources it makes more sense to use weak
> e-Tags, and so especially if one were to create a  :weakEtag relation
> on an LDPR it would be the type of relation one could use
> when describing things in a container or in a metadata file
> ( the atom-entry file )

Dear all,

I also agree on using weak ETags instead of strong ones. Therefore, my 
proposal is to replace:

[[
4.1.13 BPR server responses must contain accurate response ETag header 
values.
]]

with

[[
BPR server responses MUST use weak entity tags as response ETag header 
values.
]]

Two comments on this:
.- I think that using ETags should be a MUST, since it is the minimum 
requirement for detecting conflicts in updates.
.- I would keep things simple and not mention in the specification 
things like using :weakEtag properties in resource descriptions.

Kind regards,

>> On 2 Oct 2012, at 15:13, Linked Data Platform (LDP) Working Group Issue Tracker <sysbot+tracker@w3.org> wrote:
>>
>>> ldp-ISSUE-10 (Guidance around ETags): Include clarifications and guidance
>>> around ETags [Linked Data Platform core]
>>>
>>> http://www.w3.org/2012/ldp/track/issues/10
>>>
>>> Raised by: Raúl García Castro
>>> On product: Linked Data Platform core
>>>
>>> "4.1.13 BPR server responses must contain accurate response ETag header
>>> values."
>>>
>>> I don't know what "an accurate response" means in this context. Maybe the
>>> intention is to say that strong entity tags MUST be used (and not weak
>>> ones).
>>>
>>> If so, I would rewrite this as: "BPR server responses MUST use strong entity
>>> tags as response ETag header values.".
>>>
>>> This issue may also include the comments made about the use of ETags by
>>> Leigh Dodds
>>> (http://lists.w3.org/Archives/Public/public-ldp-wg/2012Jun/0013.html) and
>>> Steve Speicher
>>> (http://lists.w3.org/Archives/Public/public-ldp-wg/2012Jul/0006.html) which
>>> led to the need of "crafting the right set of guidance around ETags".


-- 

Dr. Raúl García Castro
http://delicias.dia.fi.upm.es/~rgarcia/

Ontology Engineering Group
Departamento de Inteligencia Artificial
Universidad Politécnica de Madrid
Campus de Montegancedo, s/n - Boadilla del Monte - 28660 Madrid
Phone: +34 91 336 36 70 - Fax: +34 91 352 48 19
Received on Monday, 4 February 2013 08:24:18 UTC

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