问题 问答题

阅读以下数据集成的叙述,在答题纸上回答问题9至问题11。

某互联网销售企业需要建立自己的电子商务平台,将所有产品信息集中在一起,为用户提供全方位的产品信息检索服务。但产品供应商大多数已经建有自己的电子商务平台,且数据独立存储,而且数据格式和数据平台有较大差异,有的供应商甚至没有采用数据库来存储商品信息。为此该企业专门成立专家组来论证其数据集成方案。

李工提出采用集中式集成方式把产品供应商的数据集中在一起,采用数据仓库技术来实现与各家供应商的数据集成。而王工提出采用松耦合的联邦数据库集成方案。专家组经过激烈讨论,认为王工方案更为合理,建议采用王工提出的集成方案。

在方案评审会上,项目组针对李工和王工的方案展开了激烈的讨论。刘工指出两种方案在实施的过程中,都存在数据源之间的语义映射和转换问题,都会带来数据集成的不确定。请简要说明产生不确定的原因。

答案

参考答案:

数据集成系统依靠模式映射来指明数据源中的数据和中介所用数据之间的语义关系,但映射过程中可能发生不确定性,其原因有:

(1)数据源与中介模式之间的语义映射可能是近似的。

(2)用户不熟悉模式或系统的域太宽,不能提供基于表单式的查询接口,需要使用关键字查询,但将关键字查询转换成一组候选的结构化查询时,会带来不确定性。

(3)数据常常是使用信息获取技术从非结构化数据源获取的,而这些获取技术一般只是“大致可用”,所取得的数据可能是不确定的。

解析:

本问题考查在数据集成过程存在的不确定性问题。问题1和问题2中实际已经明确了集成过程中存在不确定性。主要的原因在于数据集成系统依靠模式映射来指明数据源中的数据和中介所用数据之间的语义关系,但映射过程中可能发生不确定性。具体原因有:

(1)数据源与中介模式之间的语义映射可能是近似的。实际系统中往往很难有非常精确、完整的语义映射。

(2)用户不熟悉模式或系统的域太宽,不能提供基于表单式的查询接口,需要使用关键字查询,但将关键字查询转换成一组候选的结构化查询时,会带来不确定性。

(3)数据常常是使用信息获取技术从非结构化数据源获取的,而这些获取技术一般只是“大致可用”,所取得的数据可能是不确定的。

因此,在本试题中,无论采用数据仓库或者联邦数据库集成方案,都存在数据源之间的语义映射和转换问题,都会带来数据集成的不确定。

单项选择题
阅读理解

Everybody is afraid of something.That’s what more than 1,700 kids told us when we asked them about fears and scary stuff.We gave kids a list of 14 scary things and asked which one frightened them most.Here are the top 5 answers from our survey (调查):① Scary movies and TV shows;②Scary dreams;③Thunderstorms,hurricanes(飓风);and other horrible weather;④War and terrorism (恐怖行动);⑤Sounds heard at night.

But not everyone is afraid of the same thing.And what makes one person scared can be of no big deal for someone else.Plenty of kids said their biggest fear wasn’t on our list.

What is fear?

Fear is a feeling that eyeryone has—it’s programmed into all of us—and that’s a good thing because fear is there to protect us.We’re born with a sense of fear so we can react to something that could be dangerous.The baby cries,and their mom comes over to comfort him or her,helping the baby feel safe and OK again.Real vs.Pretend

The best way to get over a fear is to get more information about it.As kids get older,they understand more and start seeing the difference between what is real and unreal.So when William’s imagination leads him to think of witches,he can tell himself,“Wait a minute.They’re only pretend things.I don’t need to worry about them.”

The same goes for the dark.A kid’s imagination can start playing tricks when the lights go out.What’s under my bed?Is that a thief I hear?With the help of a parent,kids can get more comfortable in the dark.Using a nightlight or shining a flashlight under the bed to see that there’s nothing there can help kids fight that fear.

小题1:What did the writer find out from the survey?

A.Some people have never experienced fear.

B.Kids don’t like watching scary movies.

C.All people are afraid of something.

D.People often cry loudly when they are scared.小题2:What is Paragraph 2 mainly about?

A.The list of fears is not complete.

B.The things people fear are of no big deal.

C.Kids have more fears than people think.

D.People are afraid of different things.小题3:In the writer’s opinion,________.

A.having a sense of fear is not a bad thing

B.babies have a weak sense of fear

C.fear is not something that we are born with

D.not all people can react to dangerous things