Matt McAlister writes how the site combines both freeform and structured tags:
What I like most in this new architecture is that the related links are now driven by del.icio.us. Our edit team is tagging content in del.icio.us. The engineers are pulling down the del.icio.us RSS feeds. And then we create matching logic based on the common tags. We also link back out to del.icio.us pages via the tags for the article on display.
This is a first step with several more ideas for leveraging tags coming soon. We need a more densely tagged data set behind us before some of the other plans can become real. The accuracy of the related links will also be a little shady, I’m sure, until we get more sophisticated with our tagging. But we’re all excited about the possibilities for the site now that we have these tags. New ideas seem to crop up daily.
Our lead engineer Derek Butcher defined this problem in an interesting way. “Structured tags give you low precision but high volume. Freeform tags give you high precision but low volume.”