问题 问答题 简答题

试述概念模式在数据库结构中的重要地位。

答案

参考答案:

概念模式是数据库中全部数据的整体逻辑结构的描述。它由若干个概念记录类型组成。概念模式不仅要描述概念记录类型,还要描述记录间的联系、操作、数据的完整性、安全性等要求。数据按外模式的描述提供给用户,按内模式的描述存储在磁盘中,而概念模式提供了连接这两级的相对稳定的中间观点,并使得两级的任何一级的改变都不受另一级的牵制。

阅读理解

阅读理解。

     A history teacher was talking to his class about the ancient Romans (古罗马人). "They were very strong,

brave people, and they were good soldiers, too," he said."They always wanted to have strong bodies, so they

played a lot of games."

     "Did they like swimming?" one of the girls asked. "That makes people strong." She was very good at

swimming. "Oh, yes, some of them swam a lot," the teacher answered. Then he told them a story about a

famous Roman. "There was a big, wide river in the middle of Rome," he said, "and one man swam across it

three times every day before breakfast!"

     The girl laughed when she heard this. "Why are you laughing?" the teacher asked her angrily. "Did I say

something interesting?" "Well, sir," the girl answered, "Why didn't he swim across the river four times to get

back his clothes back?"

1. The ancient Romans played many games because ______.

A. they were not old enough

B. they were free

C. they wanted to be strong

D. they were not brave

2. The teacher taught ______.

A. swimming

B. English

C. history

D. P.E.

3. The girl asked the teacher if (是否) the Romans like swimming because ______.

A. she was a good swimmer

B. the teacher was good at swimming

C. she was going to learn swimming

D. she didn't like swimming 

4. The underlined (划线的) word "them" means here ______.

A. the teachers

B. the girls in the class

C. the Romans

D. Strong, brave people

5. Why did the girl laugh?

A. Because the teacher was interesting.

B. Because the man swam without (没有) breaast.

C. Because the man couldn't swim at all.

D. Because she didn't understand the teacher.

单项选择题