试题与答案

在数据库系统中,()用于对数据库中全部数据的逻辑结构和特征进行描述。其中,外模式、模

题型:单项选择题

题目:

在数据库系统中,()用于对数据库中全部数据的逻辑结构和特征进行描述。其中,外模式、模式和内模式分别描述()层次上的数据特性。

在数据库系统中,()用于对数据库中全部数据的逻辑结构和特征进行描述。

A.外模式

B.模式

C.内模式

D.存储模式

答案:

参考答案:B

解析:

本题考查数据库系统基本概念方面的基础知识。 在数据库系统中,模式用于对数据库中全部数据的逻辑结构和特征进行描述,即模式用于描述概念视图层次上的数据特性。外模式也称为用户模式或子模式,是用户与数据库系统的接口,是用户用到的那部分数据的描述,即外模式用于描述用户视图层次上的数据特性。内模式也称为存储模式,是数据物理结构和存储方式的描述,即内模式用于描述内部视图层次上的数据特性,是数据在数据库内部的表示方式。

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Today, we’ll talk about what other effects watching TV might produce on children. Children should be (1) a lot of television, many experts and parents agree, but there is at least one circumstance when it might be beneficial: (2) . A recent study conducted by Italian researchers found that children (3) immediately preceding and during blood tests experienced less pain than children whose mothers (4) during the procedure, or children whose mothers were present but (5) .
The research, led by Carlo Brown, MD, at the University of Siena, is published in the Archives of Disease in Childhood. (6) the study. None received any type of anesthesia; the children and their mothers (7) . Both the group whose mothers attempted to distract them from the blood tests and those whose mothers simply observed reported (8) than the group who watched cartoons. For that group, the levels of pain were less and the children were better able to (9) .
One of the possible explanations is that children might have (10) during the procedures, exacerbating their perception of pain. "The higher pain level reported by children during (11) shows the difficulty mothers have in interacting positively (12) in their children’s life," the authors write.
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Another possibility offered for consideration is the notion that the (16) might release pain-quelling endorphins. Endorphins, (17) produced by the pituitary gland, resemble opiates in their ability to produce analgesia and a sense of well-being. In other words, they might (18) .
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