1. Department of Information Engineering, University of Brescia, Brescia, Italy. E-mail: federico.cerutti@unibs.it
2. Institute for Web Science and Technologies, University of Koblenz-Landau, Germany. E-mail: thimm@uni-koblenz.de
3. School of Computing and Engineering, University of Huddersfield, Huddersfield, United Kingdom. E-mail: m.vallati@hud.ac.uk