问题
单项选择题
在数据库系统中，用户所见的数据模式为( )。
A．概念模式
B．外模式
C．内模式
D．物理模式
答案
参考答案：B
解析： 外模式也称用户模式，是用户的数据视图，也是用户所见到的数据模式。
搜题请搜索小程序“爱下问搜题”
在数据库系统中，用户所见的数据模式为( )。
A．概念模式
B．外模式
C．内模式
D．物理模式
参考答案：B
解析： 外模式也称用户模式，是用户的数据视图，也是用户所见到的数据模式。
A well-known speaker started his speech by holding up a $20 bill. In the room of 200, he asked, “What is this piece of 1 and is it worth anything?” Hands started going up. “It is a $20 bill, encashable(可兑现的) in international and national 2 .”replied one of the 3 who raised their hands. The speaker continued, “I am going to give this $20 to one of you, but first, let me do this.” He continued to crumple the 20 dollar bill using both his hands. He then 4 it and asked, “Who still wants it?” Still the hands were up in the air. “Well,” he said, “what if I do this?” He dropped it on the 5 and started to step on it. He picked up the crumpled and 6 bill and said, “Now, who still wants it?” 7 went back into the air. “I think this bill is still 8 its value”, said a young man in an unsure 9 . “We can still use the bill to 10 goods worth 20 dollars,” said the other people. “My friends, you have all learned a very 11 lesson in this exercise that we are just through with. You’ve 12 that I can crumple the $20 bill during the process as the effects can be seen clearly. 13 , no matter what I did to the piece of paper, you were 14 in your mind that my actions did not actually decrease its 15 . It was still worth $20.” “Many times in our lives, we feel like as if we are 16 , crumpled, and ground into the dirt by the decisions we make and the circumstances that come our way. We feel as though we are 17 ; but no matter what happened or what will happen, please 18 , you will never lose your value.” Values that you keep in your heart will always 19 you from a difficult situation. Dirty or clean, crumpled or not, you are still priceless to those who love you. The worth of our lives comes, not in what we do or who we know, but by ...WHO WE ARE.” “You are 20 — don’t ever forget it.”
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