  Collaborative tagging describes the process by which many users add metadata
in the form of keywords to shared content. Recently, collaborative tagging has
grown in popularity on the web, on sites that allow users to tag bookmarks,
photographs and other content. In this paper we analyze the structure of
collaborative tagging systems as well as their dynamical aspects. Specifically,
we discovered regularities in user activity, tag frequencies, kinds of tags
used, bursts of popularity in bookmarking and a remarkable stability in the
relative proportions of tags within a given url. We also present a dynamical
model of collaborative tagging that predicts these stable patterns and relates
them to imitation and shared knowledge.
