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Re: Design problem with "HTTP vocabulary in RDF"

From: Shadi Abou-Zahra <shadi@w3.org>
Date: Tue, 17 Oct 2006 12:51:36 +0200
Message-ID: <4534B5B8.5030901@w3.org>
To: Johannes Koch <johannes.koch@fit.fraunhofer.de>
Cc: public-wai-ert@w3.org

Hi,

On a related issue, I was wondering about the significance of the order 
of the http request/response header pairs in EARL. To reconstruct a test 
subject, one would need to know the precise sequence of the 
client/server interaction. This would be especially important for AJAX 
applications and other dynamic Web content.

While this is clearly more an EARL issue rather than a a design problem 
with the "HTTP Vocabulary in RDF" document, it is somewhat related and 
worth discussing in the context. Are there other restrictions that we 
need to consider?

Regards,
   Shadi


Johannes Koch wrote:
> 
> Hi Charles
> 
> Charles McCathieNevile schrieb:
>>> Assuming we have two content-encodings (first gzip, then compress), 
>>> the HTTP response would contain the header:
>>>
>>>    Content-Encoding: gzip, compress
>>>
>>> in RDF/XML:
>>>
>>>    <http:content-encoding>gzip, compress</http:content-encoding>
>>>
>>> AFAIK this could also appear as two headers:
>>>
>>>    Content-Encoding: gzip
>>>    Content-Encoding: compress
>>>
>>> in RDF/XML:
>>>
>>>    <http:content-encoding>gzip</http:content-encoding>
>>>    <http:content-encoding>compress</http:content-encoding>
>>
>> This is wrong. It should be
>>
>>     <http:content-encoding>tar, gzip</http:content-encoding>
>>
>> since it describes a single encoding (which happens to be the result 
>> of applying multiple transformations).
> 
> This was only an example. See section the last paragraph of 4.2 of HTTP 
> 1.1 (<http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2>):
> 
>    Multiple message-header fields with the same field-name MAY be
>    present in a message if and only if the entire field-value for that
>    header field is defined as a comma-separated list [i.e., #(values)].
>    It MUST be possible to combine the multiple header fields into one
>    "field-name: field-value" pair, without changing the semantics of the
>    message, by appending each subsequent field-value to the first, each
>    separated by a comma. The order in which header fields with the same
>    field-name are received is therefore significant to the
>    interpretation of the combined field value, and thus a proxy MUST NOT
>    change the order of these field values when a message is forwarded.

-- 
Shadi Abou-Zahra     Web Accessibility Specialist for Europe |
Chair & Staff Contact for the Evaluation and Repair Tools WG |
World Wide Web Consortium (W3C)           http://www.w3.org/ |
Web Accessibility Initiative (WAI),   http://www.w3.org/WAI/ |
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Received on Tuesday, 17 October 2006 10:51:48 GMT

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