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

From: Mark Nottingham <mnot@mnot.net>
Date: Wed, 3 Dec 2008 21:39:05 +1100
Cc: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>, Eran Hammer-Lahav <eran@hueniverse.com>, Drummond Reed <drummond.reed@cordance.net>
Message-Id: <3E24A925-128B-4E1D-A2F5-D615901E306E@mnot.net>
To: Phil Archer <phil@philarcher.org>

I think the key is to define the semantics of rel vs. rev well enough  
that a relation doesn't necessarily have to say something about them,  
but that it still can without conflicting.

Yes, that's a fine line to walk.


On 03/12/2008, at 8:53 PM, Phil Archer wrote:

> I'd just like to jump in on one point:
>
> Eran Hammer-Lahav wrote:
> [..]
>>>>>  Each link-value MUST have at least one "rel" or "rev" parameter
>>>>> whose
>>>>>  value indicates the relation type.  If the "rel" parameter is
>>> used,
>>>>>  it indicates that the link's direction for that relation type is
>>>>>  outbound; if the "rev" parameter is used, the given relation
>>> type's
>>>>>  direction is inbound.
>>>> Is 'rev' considered as authoritative as 'rel' (as in, 'type' is  
>>>> non-
>>>> authoritative, just a hint)? Forward looking links using 'rel' are
>>>> clearly authoritative as they indicate the view-point of the
>>>> resource, which has the authority to declare its own perceive links
>>>> to other resources. However, 'rev' can go both ways. It seems to be
>>>> semantically equivalent to an identical 'rel' coming from the  
>>>> linked
>>>> resource. For example:
>>>>
>>>> Resource A: Link: <http://example.com/b>; rel="friend"
>>>> Resource B: Link: <http://example.com/a>; rev="friend"
>>>>
>>>> If the two are semantically identical, 'rev' must be non-
>>>> authoritative as it serves as a hint as to what another resource
>>>> view the relationship as: "A declares B to be <<its friend>>, B
>>>> hints that A <<declares B its friend>>". However, if 'rev' is meant
>>>> to be authoritative, the two links above cannot be semantically the
>>>> same, as they read: "A declares B to be <<its friend>>, B declares
>>>> that A <<consider it a friend>>". The question is, is 'rev' simply
>>>> an implied 'rel' from the other direction (and so, non-
>>>> authoritative), or 'rev' is a reverse "opinion" of 'rel' which is
>>>> completely relative to the resource regardless of any actual 'rel'
>>>> from the other direction (and so, authoritative).
>>> This draft isn't attempting to establish a framework for semantics  
>>> or
>>> trust, and I'm tempted to take out anything that might imply this...
>> I think at a minimum it needs to clearly define the relationship  
>> between 'rel' and 'rev'. This is why I liked it better when 'rev'  
>> was dropped. If you only have 'rel', you can express 'rev' with  
>> another 'rel' value, and that will solve my issue. If you keep  
>> both, I can't see how you can avoid explaining their relationship  
>> to one another as listed in the example above.
>
> I just wrote out an argument for why I felt it was important to keep  
> rev... and realised that my own arguments convinced me that it  
> probably isn't needed for HTTP Link after all. The arguments over  
> the relative authority and semantics of rel and rev links is pretty  
> compelling.
>
> And yet, and yet... I would still be concerned to see it go because  
> it is *really* useful in RDFa. HTML 5 has dropped rev for the link  
> element and if the tide is against keeping rev in HTTP Link then the  
> impression being given might be that rev is deprecated everywhere.  
> Even though that is not what is being said or implied here, it could  
> lead to future confusion.
>
> Phil.
>
> -- 
>
> Phil Archer
> w. http://philarcher.org/


--
Mark Nottingham     http://www.mnot.net/
Received on Wednesday, 3 December 2008 10:39:44 GMT

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