1. Department of Information, ZiBo Normal College, Zibo 255130, China
2. Center for International Education, Philippine Christian University, Manila 1004, Philippines
3. School of Computer Science and Technology, Shandong Jianzhu University, Jinan 250101, China
4. School of Information Science and Engineering, Linyi University, Linyi 276000, China
5. School of Software, Shandong University, Jinan 250101, China