Have I mentioned that syndicating microformats is hot. That it's important? That it's possibly one of the most important things in syndication? Ever?
Well, I have now.
Avoiding plain XML and presentational markup from Tantek Çelik is a collection of links and observations. The takeaway for me is that if given the choice between enhancing an already semantically rich format like XHTML to carry the data you want or creating new elements in new namespaces, choose the former rather than the latter.
The marketing message of XML has been for people to develop their own tags to express whatever they wanted, rather than being stuck with the limited predefined tag set in HTML. This approach has often been labeled "plain XML" or "generic XML" or "SGML, but easier, better, and designed just for the Web
The problem with this approach is that while having the freedom to make up all your own tags and attributes sounds like a huge improvement over the (mostly perceived) limits of HTML, making up your own XML has numerous problems, both for the author, and for users / readers, especially when sharing with others (e.g. anything you publish on the Web) is important.
Of course, if you are syndicating microformats then that means that someone had to publish that information, so we also get a nice intersection of the Atom Publishing Protocol and microformats. I've outlined how microformats should interact with the APP on the [atom-protocol] mailing list.
If you have any doubt how important it is to get this right in the APP then go listen to Adam Bosworth's "Database Requirements in the Age of Scalable Services" [via lesscode.org].
To quote Sam Ruby:
My theory is that most of the interesting metadata is in the content.