The Internet Engineering Task Force (IETF) has published a Request for Comment on a proposed standard for link relations across multiple web formats. From rel="stylesheet" to rel="bookmark," rel="payment," and rel="me," according the the consensus of the IETF community members, link relations are now first class citizens with a centralized Registry where they can be found. The IETF is a nearly 25 year-old Internet standards body.

What does that mean? "Web linking is the most fundamental web building block," says Yahoo! standards wonk Eran Hammer-Lahav. "Typed links - links with a clear semantic meaning - existed on the web since the very beginning, but for the most part lacked any generally acceptable definition... Agreeing on what a link type means across formats is critical for a semantically rich web, in which links are used to provide a richer user experience, as well as better search and automation features."

Above: Seven of the forty two Link Relations currently included in the Registry

IETF RFC 5988 is the document authored by Yahoo's Mark Nottingham for the IETF that explains the standard and this is the registry where you can find the 42 relations that have been accepted so far.

Hammer-Lahav continues:

"What the new RFC does is establish a registry and a simple process for defining new link relation types across formats (HTML5, XRD, Microformats, HTTP headers, ATOM, etc.).

"What is important about the new registry is its lightweight approach, allowing most stable documents to be used as reference specifications for new relation types. The process is used as a sanity check, and not as another bureaucracy slowing down innovation."

Hammer-Lahav says the HTML5 community has been particularly active in submitting Rels for inclusion in the registry. See also the Web Hypertext Application Technology Working Group's HTML5 rel directory. (Details)

Rich links, expressed across multiple languages, in a standardized semantic format, promise to act as a platform where programatic analysis can be performed on scale - making it far easier than ever before to bring together diverse resources from all around the web to create new experiences for application users.

Below: The Firefox extension Identify uses the rel="me" code to string together all the social networks a person uses when looking at their profile on a single network.

The rel="me" link, for example, has enabled services like the Google Social Graph API to string together semantically marked-up profile pages owned by a single person across multiple different sites and social networks. That makes it easy to draw a picture of who a person is across different services they use, because their profile pages link out to their blogs or Twitter accounts, for example, using the rel="me" link relation.

That kind of cross-site functionality could be built for everything from bookmarks to content licenses to payments and more if the IETF's new web link relations markup proliferates.