问题 填空题

数据的独立性分为逻辑独立性与物理独立性。当数据的存储结构改变时,其逻辑结构可以不变,因此,基于逻辑结构的应用程序不必修改,这称为______。

答案

参考答案:物理独立性

解析: 数据的独立性是指数据和应用程序相互独立,分为物理独立性和逻辑独立性。其中物理独立性是指数据的物理结构(包括存储结构、存取方式)改变时,不需要修改应用程序。而逻辑独立性是指当逻辑结构改变时,不需要修改应用程序。

阅读理解

阅读下面短文,把A~D四个句子填入文中空缺处(1~4), 使短文内容完整正确,然后完成第5题。

     Babies sleep for up to eighteen hours a day. Sleep, no one can live without it. 1______ 

     Research (研究) by the National Sleep Foundation in Washington says that we all need eight hours' sleep

every night. Scientists have found that people who sleep for less than six and a half hours a night are more

often ill than people who sleep for eight hours. 1______  "Workaholics (工作狂)" who sleep for less than five

hours often die young, and do less well at work.

     It also says that the idea that we need less sleep as we get older is untrue." People have no idea how

important sleep is to their lives," Dr Thomas Roth, director of the Foundation says," 3______ "

     "But not too much of it," says Professor Jim Horne." Sleep is like food and drink," he believes:" 4______ 

" Professor Horne studied a group of people who could spend as hours as they wanted in bed; after ten hours

they didn't find it any easier to get up in the morning. And people who sleep for more than nine hours a night

die younger than people who usually sleep for seven or eight.

A. But how much do we really need?

B. You would always like to have a little bit more, but that doesn't mean you need it.

C. Good health needs good sleeps.

D. Going without sleep also increases the chance of illness.

5. What's the best title for this passage?

A. Children and Sleep

B. The Secrets of Sleep

C. Sleep and Work

D. Are You Having Enough Sleep?

单项选择题