中文摘要：

Yi-Song Wang is a member of China Computer Federation. He received the B.S., M.S. and Ph.D. degrees from Guizhou University in 1998, 2004 and 2007, respectively. He has been a post-doctoral researcher in Hong Kong University of Science and Technology, and he is currently a post-doctoral researcher of the Department of Computing Science in the University of Alberta. His main research interests contain artificial intelligence, knowledge representation and reasoning, and logic programming.E-mail：ys_wang168@yahoo．com．cn Corresponding Author Ming-Yi Zhang is a member of China Computer Federation. He received the B.S. and M.S. degrees in mathematics from Guizhou University in 1965 and 1980, respectively. He is a professor in Applied Mathematics Institute at the Guizhou Academy of Sciences. His research interests include computer science, artificial intelligence, nonclassical logics and their applications, non-monotonic reasoning and logic programs. E-mail：Zhangmingyi045@yahoo．com．cn； Jia-Huai You received his Ph.D. degree in computer science from University of Utah in 1985. He held a visiting position at Rice University during 1985-1986, and joined the Department of Computing Science at University of Alberta in 1986, and is now a professor. His general research interest is in knowledge representation and reasoning, declarative problem solving, and various techniques for solving constraints. His research involves： logics of non-monotonic reasoning, constraint programming, answer set programming, abduction, and Boolean satisfiability. He is currently on the editorial board of the Journal of Artificial Intelligence Research.you@cs．ualberta．ca