在并发控制中，事务是数据库的逻辑工作单位，是用户定义的一组操作序列：一个程序可以包含多个事务，事务是并发控制的 【11】 。
参考答案：单位
解析： 事务是数据库的逻辑工作单位，是用户定义的一组操作序列。如在关系数据库中，一个事务可以是一组SQL语句、一条SQL语句或整个程序。通常情况下，一个应用程序包括多个事务。DBMS的并发控制是以事务为单位进行的。
Mrs. Green has_31_children ,one is Tom,_32_is Ann.Tom is seven years old, and Ann is two years younger. Tom goes to school,but Ann_33_.When Tom is at home, he often_34_with Ann.Usually he's very _35_to his little sister. One day the two children are playing _36_the garden,Ann begins to cry. Their mother _37_over and asks ,"_38_are you crying ,Ann?" "Tom breaks(弄坏)my toy dog,"says Ann. "_39_does he break it?" "I hit(打) him on the head(头)_40_it,"says Ann. 小题1:Ａ. one B.two C.three D.four
|