Department of Computer Science, Xiamen University, China.|Department of Computer Science, Xiamen University, China.|Department of Computer Science, Xiamen University, China.|ITOP Section, DNB Bank ASA, Solheimsgaten, Bergen, Norway.|Universidad Politécnica de Madrid (UPM) Campus Montegancedo s/n, Boadilla del Monte, Madrid, Spain.|Department of Computer Science, Xiamen University, China.|Department of Computer Science, Xiamen University, China.