Tagging tags

I like the classification system presented in "The Structure of Collaborative Tagging Systems" (Scott A. Golder and Bernardo A. Huberman,Information Dynamics Lab, HP Labs):

1. Identifying What (or Who) it is About.
Overwhelmingly, tags identify the topics of bookmarked items. These items include common nouns of many levels of specificity, as well as many proper nouns, in the case of content discussing people or organizations.

2. Identifying What it Is.
Tags can identify what kind of thing a bookmarked item is, in addition to what it is about. For example, article, blog and book.

3. Identifying Who Owns It.
Some bookmarks are tagged according to who owns or created the bookmarked content. Given the apparent popularity of weblogs among Delicious users, identifying content ownership can be particularly important.

4. Refining Categories.
Some tags do not seem to stand alone and, rather than establish categories themselves, refine or qualify existing categories. Numbers, especially round numbers (e.g. 25, 100), can perform this function.

5. Identifying Qualities or Characteristics.
Adjectives such as scary, funny, stupid, inspirational tag bookmarks according to the tagger’s opinion of the content.

6. Self Reference.
Tags beginning with “my,” like mystuff and mycomments identify content in terms of its relation to the tagger.

7. Task Organizing.
When collecting information related to performing a task, that information might be tagged according to that task, in order to group that information together. Examples include toread, jobsearch. Grouping task-related information can be an important part of organizing while performing a task (Jones et al. 2005).

While their system is Del.icio.us-specific, it is almost general enough to apply to many of the other tagging systems as well.

Such classifications can be important building blocks for making tagging more usable for the average joe, by leading them through the tagging process in a more guided, structured way.