Let's start with trackback, since it is the most powerful of the new standards we've implemented. Trackback is a piece of technology that works in the background, communicating between servers. It lets one server 'ping' another server to 'tell it' about some action a user has made - provided of course that both servers implement the trackback standard. In the web-logging world, trackback has mostly been used to allow disparate writers - using disparate systems - to create distributed discussions across multiple sites. It allows a user on site-A, who links to a piece of content on site-B, to 'tell' site-B about that link. Trackback has also been used to share common categorical metadata terms for posts across mutliple sites, and has many other potential uses, which we'll touch on later in this document.

An example:

For instance, if a blogger-A encounters an interesting piece of content on Blog-B, and has something to say about it, she could of course leave a simple comment on Blog-B, but then her own readers would only come across it if they happened to read that item on Blog-B. With trackback, she can, instead, write about the Blog-B content on her own Blog-A, and have her blogging server software 'send a trackback ping' to Blog-B to inform it about this. The two entries are now two-way linked; Blog-A's entry includes a link to the Blog-B item it is discussing, while Blog-B's item includes a link back to the item which 'pinged' it (and which, presumably, has something to add to its content).

Impact on web-logging culture:

In practice, this has created an explosion of cross-annotation and link-cascading, and a very interesting culture of mutual linking and distributed conversation. There are two very interesting differences between the kinds of discussion emerging from weblogging trackbacks and those supported by conventional online forums. The discussions which emerge are structurally quite different from the thread-tree discussions found in online forums. Typically, blog entries will either have no trackbacks at all, or will be intensively linked-to, and become part of extremely non-tree-like trackback discussion branchings and loops. The number of potential entry-points into the discussion is also much higher in trackback-nets as opposed to thread trees: In emergent trackback nets, every node - being part of a particular writer's discursive structuring and readership base - will have its own range of ways of being discovered by users from a range of communities andinterests; in tree-structured discussion forums, the top-level discussion topic, on the site hosting the forum, is the only entry point.

What we have done:

We have created server-side software which implements trackbacks 'out' and 'in' for any content on our servers. We have also begun the implementation of user-interfaces for leveraging this power. There are two aspects to trackback: 'out' (pinging other servers, or other content on our own servers) and 'in' (receiving pings and associating their content with ours):

'out':

We can send a trackback ping to any compliant server to 'tell it' about content on our sites which reference it. On our test server, for instance, if a user adds a link to a discussion item, the system will try to contact the target of that link with a trackback ping, so that the content being linked to can link back to our discussion item. Of course, we can also use this within our own sites as a mechanism for connecting two pieces of content.

'in':

We can receive trackback pings from any compliant server, to tell our content that it has been referenced elsewhere, and also 'expose' our content for 'auto-discovery' of trackback urls. On our test server, for instance, if someone 'blogged' a piece of content, the details of their blog entry would be displayed in a little portlet within our site alongside our content.

Many potential new features:

It is important to realise that the examples given above are just a sampling of the new features that can be explored now that we have trackback working behind the scenes. We'll touch on some of the new possibilities in the second half of this document ('Why implement these new ingredients?')

Where to find out more:

Most writing about trackback is rather technical, but you can get the gist by scanning the first document linked-to below, and by visiting some sites which make use of trackback and following some of thetrackback links there ( URLs follow - you can generally find trackbacks for a blog entry either listed, or linked-to, at the bottom of the text for that entry)

• http://www.movabletype.org/trackback/beginners
• http://www.plasticbag.org/archives/2003/03/observation_on_the_trackback_how_to.shtml
• http://weblogs.mozillazine.org/hyatt/

New features based on trackback:

The new features we are planning, based on trackback, are covered separately in the 'Why implement these new ingredients?' section below.