1. Department of Computing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
2. Department of Systems Engineering and Engineering Management, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
3. Départment d’Informatique et Recherche Opérationnelle, Université de Montréal, C.P. 6128, Succ Centre-Ville, Montréal, Québec, Canada