1. GESIS - Leibniz Institute for the Social Sciences, Cologne, Germany
2. Institute of Computer Science, FORTH-ICS, Heraklion, Greece
3. Chongqing University of Technology, Chongqing, China
4. GESIS - Leibniz Institute for the Social Sciences, Heinrich-Heine-University, & L3S Research Center, Cologne, Düsseldorf & Hannover, Germany