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Re: Feedback for draft-nottingham-http-link-header-03

From: Roy T. Fielding <fielding@gbiv.com>
Date: Wed, 10 Dec 2008 13:19:30 -0800
Message-Id: <9193123F-63F1-452B-A0D1-B97467DB3119@gbiv.com>
Cc: Julian Reschke <julian.reschke@gmx.de>, Mark Nottingham <mnot@mnot.net>, HTTP Working Group <ietf-http-wg@w3.org>
To: Yves Lafon <ylafon@w3.org>

On Dec 10, 2008, at 3:01 AM, Yves Lafon wrote:

> On Wed, 10 Dec 2008, Julian Reschke wrote:
>
>>
>> Mark Nottingham wrote:
>>> ...
>>>       <t>HTML4 also has a "rev" parameter for links that allows a  
>>> link's relation to be reversed. The Link header
>>>         has a "rev" parameter to allow the expression of these  
>>> links in HTTP headers, but its use is not encouraged,
>>>         due to the confusion this mechanism causes as well as  
>>> conflicting interpretations among HTML versions.</t>
>>> ...
>>
>> OK, it seems I'm missing something here. Could somebody explain to  
>> me, what the conflicting interpretations are, and which we prefer  
>> (and why?)?
>>
>> HTML2 (<http://tools.ietf.org/html/rfc1866#section-5.7.3>):
>>
>>    REL
>>            The REL attribute gives the relationship(s) described by
>>            the hyperlink. The value is a whitespace separated list
>>            of relationship names. The semantics of link
>>            relationships are not specified in this document.
>>
>>    REV
>>            same as the REL attribute, but the semantics of the
>>            relationship are in the reverse direction. A link from A
>>            to B with REL="X" expresses the same relationship as a
>>            link from B to A with REV="X". An anchor may have both
>>            REL and REV attributes.
>
> In that case, it's not a reversed link, but still a normal forward  
> link, but it expressed a reversed relationship.
> A: link rel="bigger than" B
> is the same relation as
> B: link rev="smaller than" A
>
> Same relation, but different links (and different authority  
> claiming the relationship between both A and B).
> In the HTML4 example, it's reverse and forward links, so the links  
> are supposed equivalent, so not only the relation is equivalent,  
> but also the link.
> I prefer far more the "relationship equivalence" as defined in HTML2.

Yep.  The HTML2 definition is correct but easily misunderstood because
"expresses the same relationship" does not mean "is the same link".
What it should have said is that rev reverses the relationship  
semantics,
e.g., rev=made is equivalent to rel=creator.  Both define a link from  
A to B.

....Roy
Received on Wednesday, 10 December 2008 21:20:15 GMT

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