问题 单项选择题

在数据库逻辑设计中当将E-R图转换为关系模式时下面的做法哪一个是不正确的

A.一个实体类型转换为一个关系模式

B.一个联系类型转换为一个关系模式

C.由实体类型转换成关系模式的主键是该实体类型的主键

D.由联系类型转换成关系模式的属性是与该联系类型相关诸实体类型的属性的全体

答案

参考答案:D

解析:解析:由E-R图向关系模型转换,转换规则有如下三条:首先,一个实体型转换为一个关系,实体的属性就是该关系的属性,实体的码就是该关系的码,故A), C)正确。其次,一个联系也可转换为一个关系,故B)正确。第三,与该联系相连的各实体的码,以及联系的属性可转换为关系的属性。

阅读理解

阅读理解。

    Kataria is the founder of the worldwide laughter  movement.  The  celebration  of World Laughter

Day is a positive activity for world peace and is intended to build up a global sense of brotherhood

and friendship through laughter. The first "World Laughter Day" gathering took place in Mumbai,

India, on 11th January, 1998. 12,000 members from India and international Laughter Clubs attended

it. Now there are over 5,000 Laughter Clubs worldwide on all 5 continents.

     "HAPPYDEMIC" was the first World Laughter Day gathering outside India. It took place on 9th

January, two years after the Mumbai gathering.  In Copenhagen, Denmark, more than 10,000 people

gathered at Town Hall Square. The event went into Guinness Book of World Records."World Laughter

Day" is now organized on the first Sunday of May every year. Hundreds of people gather worldwide

on that day to laugh together.

     Today, many people fear widespread international terrorism. The world has never faced so much

unrest before. People are at war within themselves. Laughter is a universal language, which has the

ability to unite humanity without religion. Laughter can build a common connection between various

religions and create a new world order. The idea may sound overambitious(野心太大的), and maybe

it is. But maybe it is not. It is our deep belief that laughter and only laughter can unite the world, building

up a global sense of brotherhood and friendship.

     Studies also say that laughter helps your body do the following:  lower blood  pressure;  lighten

depression;  reduce stress; work out the heart, especially for those who are unable to perform physical

exercise. So in life, when you can laugh, you should laugh loudly and with your entire body-because it's

good for you.

1. The purpose of celebrating World Laughter Day is ________.  

A. to build up a global sense of brotherhood and friendship through laughter

B. to build a common connection between various religions

C. to reduce stress and lighten depression

D. to lower blood pressure

2. The first World Laughter Day gathering outside India took place________.

A. on 11th January, 1998  

B. on the first Sunday of May

C. on 9th January, 1996    

D. on 9th January, 2000

3. The author's attitude towards laughter movement is ________.  

A. positive                    

B. negative

C. uninterested                

D. objective

4. The passage is mainly about ________. 

A. World Laughter Day and its significance

B. the worldwide laughter movement

C. a universal language

D. laughter

单项选择题