[1] Telecom Paris, Inst Polytech Paris, Paris, France
[2] Lab Informat Paris Nord, Paris, France
[3] Vrije Univ Amsterdam, Elsevier Discovery Lab, Comp Sci, Amsterdam, Netherlands
[4] FIZ Karlsruhe, Leibniz Inst Informat Infrastruct, Karlsruhe, Germany
[5] Open Univ, Milton Keynes, Bucks, England
[6] Univ Cagliari, Cagliari, Italy