1. College of Mathematics and Informatics, Fujian Normal University, Fuzhou, Fujian, 350117, China.
2. École de technologie supérieure (ETS), Montreal, Canada.
3. University of Exeter, UK.
4. Department of Computer Science and Engineering, Sejong University, Seoul 05006, South Korea.
5. Research Chair of Pervasive and Mobile Computing, King Saud University, Riyadh 11543, Saudi Arabia, and also with the Department of Software Engineering, College of Computer and Information Sciences, King Saud University, Riyadh 11543, Saudi Arabia.