A few nits to pick with Trackback in the UserLand environment (which is, after all, a first or second draft, and thus may still be a bit malleable).
First, a tiny bit of background from my perspective. It’s important to remember that there’s more than one sort of TrackBack.
The most visible sort is post-to-post, where one post expands on, comments on, or replies to another post, and so the reply post sends a TrackBack ping to the original post (or, depending on the conversation, to several posts). That sort of ping is intended to give a reader of the original post a path to follow to later posts. It’s also important to note that doing so doesn’t actually require that the later post link to the original. Most of the time, it will, since the usual pattern is Jane posts, John replies on his weblog, and needs to include a little summary and a link to Jane’s post, so his readers will know what he’s replying to, but it’s not a part of the TrackBack contract. Suppose instead that John has a FAQ post, explaining how to do something, and Jane publishes a post asking the world how to do that something. By sending a ping from his FAQ post, John provides a link to Jane and any readers of her post to his answer, but there’s no reason to have a link in his post to her question: people already reading the answer don’t need to know the question. In that case, autodiscovery based on links in the entry isn’t enough.
Though that’s the most visible sort of TrackBack, post-to-category, or category-to-post or -category, are also very useful ways to ping. Post-to-category pings, where an individual post sends a ping to a collection of pings, rather than a particular post, is commonly used for conferences, like the O’Reilly Emerging Technology Conference, where someone just making an entry or two might send pings directly from those entries, either by autodiscovery from a link, or manually, but someone live blogging the whole conference would be more likely to just add a category for the conference, and have any post in that category ping the ETCON TrackBack URL. Category-to-category (or post-to-category) pings are also what powers things like the Internet Topic Exchange, or my pinging of the MovableBLOG sidebar. Used that way, it’s like a finer-grained form of aggregation: Richard wouldn’t want to publish links to my every post by aggregating my whole RSS feed, but by pinging just the Movable Type related posts, I can let him aggregate just the on-topic stuff.
That said, when I talk about TrackBack, I usually mean post-to-post, and that’s certainly true when I say, yet again, A TrackBack Is A Comment. I say that a lot, but
Outbound Trackback is easy for both products, inbound will be hard for Radio, where the content system may be behind a firewall. Some kind of proxy will be needed, perhaps a Manila site.
I get the feeling that even if some of the philosophy is getting through, the practical aspects aren’t. A TrackBack is a post to a script at a particular URL, including the ID number for what’s being pinged, and a name, a link, a title, and some text. A comment is a post to a script at a particular URL, including the ID number for what’s being commented on, and a name, a link, maybe an email address, perhaps a title, and some text. If you have a comment system, and want to support TrackBack, it’s just a matter of writing a script that sticks together the title and the body text, tacks a [more] link on at the end, and stores it as a comment. A system that stores them separate from comments, but can intermingle them, will be more flexible, but with a little tweaking and another script, RadioComments.UserLand.Com could be accepting TrackBack pings without much trouble.
If a content management application supports outbound Trackback, as Manila does, it can notify another site that a post points to a post on the other site. You may see a list of inbound Trackbacks in a separate window linked to the post.
I’d much prefer “a post responds to” or “a post replies to” rather than “a post points to”. We already have a way to know that a post points to a post on another site: that’s what referrers do. We also have a way to know in a cleaner, quicker way, getting just a referrer from the permalink location without anyone clicking the link: that’s Pingback. And although MT’s basic implementation (and perhaps Radio’s as well) is stuck using a popup window, because MT’s single-threaded approach can’t always afford the time to rebuild every possible page where the ping might appear before it replies and dies, there’s nothing specifically TrackBacky about that. You may see a list of inbound TrackBacks in a separate popup window, or listed at the end of the entry itself, or intermingled with (local) comments.
When you post a News Item to the home page of the site, if Trackback is turned on (by default it’s not) we scan the message text for URLs, and then read each of the pages.
Danger Will Robinson! I hope you’ve got some safeguards in place that you just didn’t happen to mention, or that Manila’s a lot better about being able to suck down enormous quantities of data: probably the most commonly reported problem with MT’s autodiscovery is “I tried to save a post, but the script keeps timing out. Well, yes, I did link to a 5MB MP3 with autodiscovery turned on.” Better to pick some length (I like 100K) that’s the maximum you’ll ever read before giving up. Especially if
If Automatic Pings is not turned on, we just do the auto-discovery work, and later, the user, when editing the message, may choose to ping sites that are linked to, on a case by case basis.
If I understand that right, that there are two Prefs, one to turn on TrackBack, and another to automatically ping, so that it’s possible to choose what to ping and what not to ping, by saving the entry and then editing to choose what to ping, I like it, but… only autodiscovery? A person who only occasionally wants to ping would have to turn on TrackBack, and turn off automatic pinging, and then have his site download every single thing he links to, just for the odd ping every now and then. Isn’t there any room on the entry page to slip in a little textarea for TrackBack URLs? Add a third Pref: Trackback on or off, Autodiscovery on or off, and Automatic pinging on or off (with Automatic pinging as a sub-pref of Autodiscovery, so that selecting Automatic pinging selects Autodiscovery), so that shotgun pingers could send pings everywhere without thinking, frequent pingers could download everything they link to and then choose what to ping, and selective pingers could just do a quick copy-n-paste when they want to ping. If not, well, it’s a lucky thing Radio users tend not to do too many big link-dump posts with links to ten or twenty things in a post, or the traffic while upstreaming, downloading everything linked to, and then sending pings, will get a bit ugly on dialup.