Database design for tagging

Social bookmarking is everywhere these days. If your're at home building the next amazing del.icio.us- or digg-clone it's important you plan the design of the database carefully. Philipp Keller shows a few variations on the post "Tags: Database schemas" and gets an enormous response in the comments.

Also read "Explaining and Showing Broad and Narrow Folksonomies" by Thomas Vander Wal (the man who coined "folksonomy"). Interesting reading about "broad" and "narrow" ways of user-tagging.