  A distributed classification paradigm known as collaborative tagging has been
widely adopted in new Web applications designed to manage and share online
resources. Users of these applications organize resources (Web pages, digital
photographs, academic papers) by associating with them freely chosen text
labels, or tags. Here we leverage the social aspects of collaborative tagging
and introduce a notion of resource distance based on the collective tagging
activity of users. We collect data from a popular system and perform
experiments showing that our definition of distance can be used to build a
weighted network of resources with a detectable community structure. We show
that this community structure clearly exposes the semantic relations among
resources. The communities of resources that we observe are a genuinely
emergent feature, resulting from the uncoordinated activity of a large number
of users, and their detection paves the way for mapping emergent semantics in
social tagging systems.
