1. School of Software, Northwestern Polytechnical University, Xian 710072, China
2. Division of Computer Science, University of Camerino, 62032 Camerino, Italy
3. National Engineering Laboratory for Big Data System Computing Technology, Shenzhen University, Shenzhen 518060, China
4. School of Computer Science, College of Science, Mathematics and Technology, Wenzhou-Kean University, Wenzhou 325015, China