1. College of Computer Science, Chongqing University, Chongqing 400044, China
2. Department of Software Engineering, Chongqing Institute of Engineering, Chongqing 400056, China
3. College of Automation, Chongqing University, Chongqing 400044, China
4. College of International Education, Chongqing University, Chongqing 400044, China
5. PetroChina Chongqing Marketing Jiangnan Company, Chongqing 400060, China