问题 单项选择题

对关系模式进行规范化的目的是( ),并避免出现插入异常、删除异常和更新异常。

A.减少数据冗余

B.提高查询速度

C.保证数据安全

D.提高查询效率

答案

参考答案:A

解析: 一个“不好”的关系数据库模式会存在数据冗余、更新异常(不一致的危险)、插入异常和删除异常4个问题。为了解决这些问题,人们才提出了关系数据库的规范化理论。规范化理论研究的是关系模式中各属性之间的依赖关系及其对关系模式性能的影响,探讨“好”的关系模式应该具备的性质,以及达到“好”的关系模式的设计算法。

阅读理解

阅读理解。

     Liu Ting is a student of Zhejiang Forestry College. One month after he went to the college, he rented

a house outside the school and took his mother there. In this small room, they began their new life. Every

morning, as soon as Liu Ting gets up, he takes his mother's blood pressure (血压)-After that, he makes

breakfast and then goes to school. In order to manage daily cost, he has a part-time job in the school's

canteen (食堂). Thanks to this job, he can have free dinners and get 50 yuan a month. Besides, he is allowed

to bring meals to his mother from the canteen every day.

     Liu Ting doesn't have time to do his homework until his mother gets to sleep late at night. The 19-year-old

boy sleeps only six hours every day. It is no surprise that he got ill. "He was absent that day. We went to his

house to see what had happened. When we arrived, we saw that both he and his mother were lying in bed

because of illness," said his classmates.

     From then on, Liu Ting's story was known by his classmates and teachers. Even more people knew his

story after it was reported on TV. People donated over 200, 000 yuan in order to treat his mother's illness.

In late 2005, a hospital in Shanghai agreed to operate (手术) on his mother. Now his mother is getting better

and better. Liu donated the rest 40, 000 yuan to set up a fund (基金) to support other poor college students.

     Liu Ting said, "I know that there are people who have a better life. I just try my best to control my life and

make it better. I'll take part in more charity activities to express my thanks to society. I am very happy when

helping others."

1. What does Liu Ting do first every morning?

A. He fetches meals from the canteen.

B. He goes to school.

C. He makes breakfast for his mother.

D. He takes his mother's blood pressure.

2. Liu Ting got ill one day because _____.

A. he ate some bad food

B. he got up too late

C. he had only a short time to sleep

D. he watched TV too much

3. We can learn from the passage that _____.

A. his mother's operation was successful

B. he kept all the rest money as his own

C. his classmates knew his story from newspapers

D. he could get 50 yuan every year

4. The passage mainly tells us that _____.

A. Liu Ting has the ability to make money

B. Liu Ting is a person with great love

C. Iiu Ting goes to college with his sick mother

D. Liu Ting is willing to help his classmates

单项选择题