1. Eindhoven University of Technology, Eindhoven, The Netherlands. E-mails: n.tax@tue.nl, n.sidorova@tue.nl, wvdaalst@pads.rwth-aachen.de
2. Bol.com, Utrecht, The Netherlands. E-mail: ealasgarov@bol.com
3. Philips Research, Eindhoven, The Netherlands. E-mail: r.haakma@philips.com
4. RWTH Aachen, Aachen, Germany. E-mail: wvdaalst@pads.rwth-aachen.de