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Re: Reviving HTTP Header Linking: Some code and use-cases

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Tue, 11 Mar 2008 10:05:33 -0400
Message-ID: <47D691AD.5000305@ibiblio.org>
To: Julian Reschke <julian.reschke@gmx.de>
Cc: ietf-http-wg@w3.org

Julian Reschke wrote:
> Harry Halpin wrote:
>>> [snip]
>> The links are to the GRDDL transform URIs themselves. And a non-licensed
>> GRDDL transformation is not technically a GRDDL transformation. That's
>> why we use Profile in our definition.
>
> Understood. But wouldn't two different link relations have the same
> semantics?
Operational semantics, yes. But one would be authorized by the creator
of the document while the other's wouldn't. I think that's a valid
distinction. One could "link" to page containing a GRDDL transform and
not want it run, because you do not trust it, it is still experimental,
etc.
>>> So, let's rephrase this: if a link relation could be a URI (or IRI),
>>> would we need Profile?
>> Explain precisely how this would work. I'm not sure what document I
>> should be looking at to explain "link relations" to me. If there's
>> another header that can do it, that might work.
>
> No, I meant the link header...:
>
> Link: <http://example.com/grddl.xslt>;
>   rel="http://www.w3.org/2003/g/data-view/transform"
Yep, that would be another way to do it, but only *if* rel allows URIs.
I thought it did not. Am I wrong?

But if there is, still think there's an argument for profile, see below.

>> I can see how there might be conflict if HTML drops Profile and HTTP
>> re-instates it. It would be better for it to be either re-instated
>> uniformly or not. But I think Profile does have a pretty good URI-based
>> extensibility case going for it.
>
> Yes, I totally agree that URI based extensibility is good. I'm just
> not sure it's good enough with Profile, given the fact it doesn't
> solve the disambiguation problem.
What profile does is provide a meta-data profile for the resource of the
URI itself, not just the links, although it can be used to disambiguate
the links (albeit imperfectly if lists of profiles and links are used).
In this manner, it's still very useful. For example, it's usage in
microformats in HTML allows microformats to have GRDDL transformations
without a centralized repository. The same case can be made for HTTP.
The only alternative is to "stick everything" in a centralized registry.

So, we could imagine a case where someone wants to use a profile URI for
their microformat-enabled page, and we want GRDDL to go to that profile
and get the GRDDL transform. I guess one could try to do this.

Link: <http://example.com/mymicroprofile>;
  rel="http://example.com/itsaprofile"

But it seems that Profile would work too:

Profile: <http://example.com/mymicroprofile>;

Again, I think I've already made a request for Link to be re-instated.
If Link is re-instated, then we'd also like URIs to be allowed in rel
fields. I think there's no argument here.

We'd also like Profile to be kept, but could probably live if an
alternate mechanism was approved, i.e. URIs in rel fields.

However, this would break existing software and so we'd have to change
it. I think the same would go for the microformat community if HTML 5
got rid of profiles.





> BR, Julian
>


-- 
		-harry

Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Tuesday, 11 March 2008 14:05:57 GMT

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