HTTP Linkage

This document is for discussion only and has no official status. It is one of three discussion documents for use at the meeting. The others are Boston 1 and, creatively, Boston 2

The charter calls for "A W3C Recommendation providing an HTTP-based mechanism for locating and accessing description resources associated with a particular Web resource."


We want to know that a resource has a DR associated with it.

We want to be able to do this irrespective of resource type, hence HTTP-based.

Want to know whether a WDR is worth fetching without doing so and parsing it. If we want to know about mobileOK, we don't want to parse a WDR that only has ICRA labels etc.


In June 2006 Mark Nottingham wrote

RFC2068 actually did that; it documented the Link HTTP header in an appendix, but by the time RFC2616 rolled around, it was gone because no-one was using it at the time. While it’s perfectly fine to use the Link header today (it’s in the registry), its disappearance confused some people, and led them to believe that they couldn’t.

To this end, I’ve submitted an Internet-Draft to re-define the Link header, just as it was before. Additionally, the draft defines a Profile header, to serve the same function as the profile attribute in HTML.

His IETF draft has expired now and he's not answering my e-mails, sadly, so I can't see what he did for a profile header. But - I recall that he was using the HTML profile to define link relationships (wrong) rather than meta tag prefixes like <meta name="dc:creator" ...> (right) so I don't think this is too much of a blow. Depending on what we decide, the WG may need to submit an RFC?

Meanwhile, here are some ideas.

In the XGR we give this example (it's straight from what we do with RDF-CL at ICRA and Segala etc.)

HTTP Response Header

Link: </cLabels.rdf>; /="/"; rel="cLabel" type="application/rdf+xml"; 

Equivalent XHTML link tag:

<link rel="cLabel" href="" type="application/rdf+xml" />

A convention is building in the RDF world of using the title attribute as a hint but this is less than satisfactory

I suggest the following approach.

Link: <$URI>; /="/"; rel="MOK ICRA" type="application/wdr+xml"; 
Link: <> /="/" rel="LinkProfile" type="text/html";

(requires registration of relationship "LinkProfile" with IANA but otherwise headers need no new definition). The rel attribute formally takes a whitespace separated list of relationships so that's in the spec already.

The idea being that the HTML document at would provide a look-up table that would match MOK with the mobileOK namespace, ICRA with its namespace and so on. A well known look-up table like one on would be enough to tell you what MOK meant without actually having to look it up.

Whilst Mark Nottingham tells us that the header is still in the registry, it would seem prudent to try and revive it officially at IETF to avoid confusion.