We describe online collaborative communities by tripartite networks,
the nodes being persons, items and tags. We introduce projection
methods in order to uncover the structures of the networks, i.e.
communities of users, genre families... <br />To do so, we focus
on the correlations between the nodes, depending on their profiles,
and use percolation techniques that consist in removing less correlated
links and observing the shaping of disconnected islands. The structuring
of the network is visualised by using a tree representation. The
notion of diversity in the system is also discussed.
