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

From: Mark Nottingham <mnot@mnot.net>
Date: Wed, 3 Dec 2008 12:37:53 +1100
Cc: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
Message-Id: <F32C5024-2288-48C0-B1C0-9C485DEE86AB@mnot.net>
To: Eran Hammer-Lahav <eran@hueniverse.com>


On 02/12/2008, at 6:33 PM, Eran Hammer-Lahav wrote:
>>
>> 1.  Introduction
>>
>>   This document defines typed link relations, independent of the
>>   context they occur in.  It does so by clarifying the status of the
>
> I think 'context' needs to be clarified to mean 'content type' or  
> 'transport'. Without the next sentence, this seems to imply that  
> instances of the Link header are not context-sensitive, which they  
> are (resource, representation, etc.).

I'm not sure what you're getting at here; this sentence isn't talking  
about the Link header at all...


>> 4.  Link Relation Types
>>
>>   Relation types are not to be confused with media types [RFC4288];
>>   they do not identify the format of the representation that results
>>   when the link is dereferenced.  Rather, they only describe how the
>>   current context is related to another resource.
>
> I think it should also clarify the fact that 'type' is non- 
> authoritative but informative (suggestion, hint). In addition, it  
> should state that 'type' should not be used to imply relationship as  
> is often the case with single-use content-types (favicon is one  
> example). It seems many people find the distinction between 'rel'  
> and 'type' confusing and the spec should make it clear how the  
> parameters relate to each other.

Yes - type needs to be defined in prose as well.


>>   The context of links conveyed in the Link header field is the
>>   representation that the header is part of.
>
> This makes sense since the header is provided in the context of the  
> representation. However, is there a way to indicate that a link is  
> persistent across representations and is not representation- 
> specific? Do 404 and 303 considered representations?

*sigh* this is the tricky bit; HTTPbis has at least one open issue on  
this. I believe the current position is that all messages have  
entities, and all entities are representations, the trick being that  
the representation isn't always of the resource which the request was  
sent to; sometimes it's an "anonymous" representation.


>>   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...


--
Mark Nottingham     http://www.mnot.net/
Received on Wednesday, 3 December 2008 01:38:35 GMT

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