3. TAGS

8. Sub-linear vocabulary growth internal time # of tags

9. del.icio.us > x 0.8

10. Tag frequency distribution

11. Preferential attachment

12. Few tags per resource

19. Distribution of strength

20. Distribution of strength ?

21. Nontrivial clustering & spam detection Clustering coefficient C(k) Average density of triangles around nodes with degree k

22. Nontrivial clustering & spam detection

23. Nontrivial clustering & spam detection k = 502

24. Looking for a k = 502 page...

26. SPAM

27. Nontrivial clustering & spam detection spam k = 502

33. Users' strategies Do users tag resources according to tag conceptual hierarchy?

34. Semantics and hierarchy For example ” Emergence of scaling in random networks” by A.-L. Barabasi and R. Albert

35. Semantics and hierarchy For example ” Emergence of scaling in random networks” by A.-L. Barabasi and R. Albert scale-free networks

36. Semantics and hierarchy For example ” Emergence of scaling in random networks” by A.-L. Barabasi and R. Albert scale-free networks networks HIERARCHICAL

37. Semantics and hierarchy For example ” Emergence of scaling in random networks” by A.-L. Barabasi and R. Albert scale-free networks WWW NON HIERARCHICAL

43. Results: strength distribution

44. Results: clustering