School of Informatics, University of Edinburgh, Edinburgh, United Kingdom.|School of Informatics, University of Edinburgh, Edinburgh, United Kingdom.|L2S-Univ. Paris Sud-CentraleSupélec, Gif sur Yvette, France.|L2S-Univ. Paris Sud-CentraleSupélec, Gif sur Yvette, France.|School of Informatics, University of Edinburgh, Edinburgh, United Kingdom.