1. Department of Computer Science and Engineering, Yanshan University, Qinhuangdao, China
2. Computer Science, TU Wien, Vienna, Austria
3. School of Computing Science, Newcastle University, Newcastle upon Tyne, U.K.
4. Faculty of Earth Sciences, China University of Geosciences, Wuhan, China
5. School of Computer Science, China University of Geosciences, Wuhan, China