What counts as tagging / a true tagging system, and what is the best way to do it? My CMS comparison (dated info: 8/08) got another mailed-in comment like Harry's at the Joomla forum in an ongoing thread about Drupal vs. Joomla where I have praised and maligned both systems in an effort to be fair. In the comparison, I indicated that Drupal and Joomla both do not have a core system for tagging but Wordpress does. At the time I wrote that I suppose I was imagining Wordpress and this sort of concept as the standard. But... Wordpress doesn't really have tagging either without extensions/plugins. It all depends on what you mean by "tagging." Apparently there is some kind of standing debate about this.

As I recall, tagging kind of evolved out of the flexible article categories in blog engines like Wordpress. Technorati started treating Wordpress categories as tags. Eventually "free tagging" seemed to become the ideal, the standard of what tagging really is or should be--being able to spontaneously make up tags for any content item as you create that item. The tags then serve as metadata keywords and allow your site to link and list all items according to their tags. You're also able to display a sorted list of all the tags used on a site, or in parts of it, possibly with a tag "cloud" that visually illustrates tag density. Tag clouds show the frequency of a tag's usage by proportionally increasing its font size in a cluster or list of multiple tags. In some cases, you might even open your content to being free-tagged by visitors or designated users with login credentials. This was termed  "folksonomy," AKA collaborative tagging, social classification, social indexing, and social tagging."

I really need to catch up on Wordpress, but I think it's correct WP can't do any of this out of the box. [Update: Basic tagging and tag lists are standard in Wordpress 2.7+ and some really nice auto-tagging or auto-recommend plugins exist for WP.] With Drupal, you can indeed do most of this with the core Taxonomy module, which has always been like "categories" but really, really flexible and too smart for its own good. With Wordpress, categories are very flexible and can be used for tagging. With Joomla, there's not much flexibility at all in its sections and categories, so the various tagging extensions for Joomla create their own fields or just play off of keywords and use the site search to generate lists of content by keyword/tag as search results pages. (That's what I'm doing here.) All of the aforementioned forms of tagging can be done via one or more extensions for Drupal, Joomla, and Wordpress.

And then there is really serious autotagging for the semantic web--via OpenCalais (which is sponsored by Reuters) and really, really nifty. Drupal has a Calais module. Wordpress has a Calais plugin. A Joomla developer participating in the 2008 Google Summer of Code was thinking about bringing Calais into Joomla last year. Discussion of the semantic web in the Joomla community seems to have slacked off since then, unfortunately.