中文摘要：

Corresponding author.Yunyan Xing is a research assistant in School of Information Systems and Management at National University of Defense Technology. She received her Ph.D. degree in control science and engineering from National University of Defense Technology in 2010. Her research fields are reliability, maintainability, and system evaluation. E-mail： xingyy2005 @ sina.com.cn Xiaoyue Wu is a professor in School of Information Systems and Management at National University of Defense Technology. He received his Ph.D. in management science and engineering from National University of Defense Technology in 2000. His research fields are reliability, maintainability and system test evaluation ＆ design. E-mail： xiaoyuewucn@ yahoo.com.cn