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

From: Eran Hammer-Lahav <eran@hueniverse.com>
Date: Thu, 4 Dec 2008 10:31:31 -0700
To: "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>, Mark Nottingham <mnot@mnot.net>
CC: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-ID: <90C41DD21FB7C64BB94121FBBC2E723412797FC964@P3PW5EX1MB01.EX1.SECURESERVER.NET>

> From: Williams, Stuart (HP Labs, Bristol) [mailto:skw@hp.com]
> Sent: Thursday, December 04, 2008 8:44 AM
>
> If you take the view, which I think is the correct view - and I think
> that you do to, that the links being claimed at least in a response,
> are between the requested resource and the resource targetted by the
> link, the question of which representation is taken as "canonicial" or
> in some sense 'supreme' becomes immaterial.

[It takes a while to get used to my style, but while I usually talk in absolutes, there are very few things I have strong opinions on (this is not one of them). I'm also really new to web architecture (I served a 10 year term in investment banking before I escaped to a web job).]

The 'canonical' question doesn't apply if you take the view that link is between resources and not representations. But it becomes an implementation concern when building an application that defines links to be between resources, and the Link header is not fully compatible with that. Resource discovery (XRDS, POWDER, OpenID, etc.) depends on links having a resource and not representation context. But again, there are easy implementation-based solutions if the spec goes the representation way.

I prefer to define links as between resources regardless of their representation mostly for the following reasons:

1. I think links should be symmetric and 'representation --> resource' isn't symmetric. 'resource --> resource' is nice and clean.
2. If a 'rel' link is defined as 'representation --> resource' that forces 'rev' to be 'resource --> representation'. It means that 'B --(rev)--> A' has nothing to do with 'A --(rel)--> B' because each is between different objects (resource / representation).
3. The other way to accomplish symmetry is 'representation --> representation' which has been rejected here before. That would shift the meaning of 'type' from a hint to an actual part of the relationship context (needed to define the representation of the linked resource in context for the link).

There are clear implications for defining link as 'representation --> resource' vs. 'resource --> resource'. One of them is the impact of the definition of the 'rel/rev' relationship. All I am asking for is clarity.

EHL
Received on Thursday, 4 December 2008 17:32:20 GMT

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