问题 问答题

【说明】
设有关于银行借贷管理系统的E-R图。图中矩形表示实体,圆表示属性,双圆表示关键字属性,菱形表示实体间的联系。为了答题的方便,图中的实体和属性同时给出了中英文说明,回答问题时只需写出英文名即可。


1. 【问题1】
根据E-R图中给出的词汇,按照“有关模式名(属性1,属性2,…)”的格式,将此E-R图转换为关系模式,并指出每个关系模式中的主码和外码,其中模式名根据需要取实体名或联系名。要求其中的关系模式至少属于第三范式。

答案

参考答案:这样的系统算不上分布式数据库系统。分布式数据库系统并不是简单地把集中式数据库系统安装在不同场地,用网络连接起来实现的(这是分散的数据库系统),它是具有自己的性质和特征。
分布式数据库系统具有以下特点:
1.数据的物理分布性。
2.数据的逻辑整体性。
3.数据的分布独立性。
4.场地的自治和协调。
5.数据的冗余及冗余透明性。
虽然上述银行的数据库系统具有性质1、3以及4和5的一部分,但关键是没有数据的逻辑整体性和不同场地之间的协调性等,这恰恰是分布式数据库系统的关键所在。因此,上述银行数据库系统算不上分布式数据库系统。

解析:

[分析]:本题主要考查分布式数据库系统的必备条件。

选择题
阅读理解

Many children use the Internet to get useful knowledge and information, and to relax in their free time. But some of them are not using it in a good way. Here are some rules to make sure you are safe and have fun on the Internet.

※Make rules for Internet use with your parents. For example, when you can go online, for how long and what activities you can do online.

※Don’t give your password(密码)to anyone else, and never give out the following information: your real name, home address, age, school, phone number or other personal information.

※Check with your parents before giving out a credit(信用)card number.

※Never send a photo of yourself to someone in email unless your parents say it’s OK.

※Check with your parents before going into a chat(聊天)room. Different chat rooms have different rules and attract different kinds of people. You and your parents will want to make sure it’s a right place for you.

※Never agree to meet someone you met on the Internet without your parent’s permission(允许). Never meet anyone you met online alone.

※Always remember that people online may not be who they say they are. Treat everyone online as if they were strangers.

※If something you see or read online makes you uncomfortable, leave the site. Tell a parent or teacher right away.

※Treat other people as you’d like to be treated. Never use bad language.

※Remember - not everything you read on the Internet is true.

小题1:The writer tells children to _________.

A.send their own photos to him

B.make rules for Internet use with parents

C.believe everything they read on the Internet

D.give out their personal information小题2:It’s good for children to ______ on the Internet.

A.give password to others

B.get useful knowledge and information

C.give out a credit card number

D.go into a chat room as they’d like to小题3:What shouldn’t be done when you are on line? _________

A.Using bad language

B.Sending messages and emails

C.Leaving the site if you feel uncomfortable

D.Treating everyone online as strangers小题4:If your parents don’t agree, never ________.

A.read anything on the Internet

B.relax in your free time

C.have a face-to-face meeting with anyone you met online

D.treat other people as you’d like to be treated小题5:The passage is mainly about _________ .

A.How to use computers

B.Surfing on the Internet

C.Information on the Internet

D.Internet safety rules