8 116 2005-09-05T14:37:24-04:00 $Date: 2005-09-11 10:27:02 -0400 (Sun, 11 Sep 2005) $ NormanWalsh 2005Norman Walsh Microformats, a technique for embedding machine readable data in human readable formats, are growing in popularity. I've added support for the hCalendar microformat in travel itineraries, but I'm not optimistic about the technique. Dan Connolly and I are travelling to Edinburgh later this month for a TAG meeting. In the course of looking at our respective online schedules, we got to chatting about microformats, specifically hCalendar. Dan's been experimenting with using it and I've obviously got calendar data on the web, so you'd think I could use it too. One of the reasons this blog exists is so that I have a place to experiment, so I spent a few hours one evening last week tinkering to get hCalendar supported on my itineraries pages. It turned out to be a little tricky because that page doesn't have all the detailed information needed to generate the event data, but I managed to work around that. Right now, only a few of the events are actually formatted with hCalendar, but over time I'll probably get all of them into that format. Microformats are becoming quite popular. Old timers like myself recognize that these are what we used to call “architectural forms” being reinvented. Exactly what constitutes a microformat is probably open to debate. On one end of the scale there are really simple things, like adding a rel attribute to anchor tags, and on the other, considerably more complex things like hCalendar and hCard which have nested structure. The idea develops pretty naturally. You start with some markup vocabulary (DocBook, XHTML, whatever you have lying around) that has an attribute that's used for specialization. In DocBook, we call it role. In XHTML, it's called class. You use it when you want to distinguish two pieces of data that are marked up with the same element. This works perfectly well on an ad hoc basis, and if you pass the document to someone who isn't familiar with your extensions, the fallback is natural and obvious. Microformats (and architectural forms, and all the other names under which this technique has been invented) take this one step further by standardizing some of these attribute values and possibly even some combination of element types and attribute values in one or more content models. This technique has some stellar advantages: it's relatively easy to explain and the fallback is natural and obvious, new code can be written to use this “extra” information without any change being required to existing applications, they just ignore it. Despite how compelling those advantages are, there are some pretty serious drawbacks associated with microformats as well. Adding hCalendar support to my itineraries page reinforced several of them. They're not very flexible. While I was able to add hCalendar to the overall itinerary page, I can't add it to the individual pages because they don't use the right markup. I'm not using div and span to markup the individual appointments, so I can't add hCalendar to them. I don't think they'll scale very well. Microformats rely on the existing extensibility point, the role or class attribute. As such, they consume that extensibility point, leaving me without one for any other use I may have. They're devilishly hard to validate. DTDs and W3C XML Schema are right out the door for validating microformats. Of course, Schematron (and other rule-based validation languages) can do it, but most of us are used to using grammar-based validation on a daily basis and we're likely to forget the extra step of running Schematron validation. It's interesting that RELAX NG can almost, but not quite, do it. RELAX NG has no difficulty distinguishing between two patterns based on an attribute value, but you can't use those two patterns in an interleave pattern. So the general case, where you want to say that the content of one of these special elements is “an abbr with class="dtstart" interleaved with an abbr with class="dtend" interleaved with…”, you're out of luck. If you can limit the content to something that doesn't require interleaving, you can use RELAX NG for your particular application, but most of the microformats I've seen use interleaving in the general case. Is validation really important? Well, I have well over a decade of experience with markup languages at this point and I was reminded just last week that I can't be relied upon to write a simple HTML document without markup errors if I don't validate it. If they can't be validated, they will often be incorrect. At the end of the day, I'm not a fan of microformats, at least not on the complex end of the spectrum. There are undoubtedly lots and lots of situations where they're the only practical answer, but if you don't have to use them, I'm not sure you should. If you want to embed data in your documents, embed data. The XML source for the individual itinerary pages, for example, doesn't use DocBook littered with role attributes to store itinerary information, it uses markup suited to that purpose: 2005-09-18T12:45:00 2005-09-18T14:30:00 BDL-RDU/AA 4695 #BDL #RDU 4695 American Airlines …]]> I think that's a better answer when it's a practical answer.