[Zhou, Pingyi;Liu, Jin] Wuhan Univ, Comp Sch, State Key Lab Software Engn, Wuhan, Peoples R China.^[Yang, Zijiang] Western Michigan Univ, Dept Comp Sci, Kalamazoo, MI 49008 USA.^[Zhou, Guangyou] Cent China Normal Univ, Sch Comp, Wuhan, Peoples R China.