1 Department of Software Engineering, School of Information Science and Engineering, Yanshan University, Qinhuangdao, China.
2 The Key Laboratory of Software Engineering of Hebei Province, Yanshan University, Qinhuangdao, China.
3 Department of Computer Science and Technology, School of Mathematics and Information Science and Technology, Hebei Normal University of Science and Technology, Qinhuangdao, China.
4 Department of Educational Technology, College of Education, Hebei Normal University of Science and Technology, Qinhuangdao, China.