DBMS的优点和缺点

1.6  Advantages and Disadvantages of DBMSs （数据库的优点和缺点）

The database management system has promising potential advantages. （数据库管理系统具有广阔的潜在优势。）

promising /pr'ɔmisiŋ/ adj. someone or something that is promising seems likely to be very good or successful.

具有promising性质的人或者物似乎可能是非常好的或者成功的。

A school has honoured one of its brightest and most promising former pupils.

Unfortunately, there are also disadvantages. （不幸，也存在缺点。）

In this section, we examine these advantages and disadvantages. (在这一节，我们学习这些优点和缺点)

Advantages (优点)

The advantages of database management systems are listed in Table 1.2 . (图1.2列出了数据库管理系统的优点和缺点。)

 TABLE 1.2   Advantages of DBMSs

Control of data redundancy 控制数据冗余	Economy of scale 经济规模
Data consistency 数据的一致性	Balance of conflicting requirement 相与冲突的需要平衡
More information from the same amount of data 同样数量的数量有更多的信息量	Improved data accessibility and responsiveness 改进数据访问和响应
sharing of data 数据共享	Increased productivity 提高生产率
Improved data integrity 数据完整性提高了
Improved security 安全性提高	Improved maintenance through data independence 通过数据独立性改善维护
Enforcement of standards 执行标准	Increased concurrency 增加并发
	Improved backup and recovery services 改进了备份和恢复服务

 

Control of data redundancy  (控制数据冗余)

As we discussed in Section 1.2, traditional file-based systems waste space by storing the same information in more than one file

(正如在1.2节讨论的，传统的基于文件系统浪费空间， 用于多于一个文件储存相同的信息。 )

For example, in Figure 1.5, we stored similar data for properties for rent and clients in both the Sales and Contracts Departments.

(例如， 在图1.5中， 在销售和合同两个部门，我们储存了相似的租金和客户属性。)

In constrast, the database approach attempts to eliminate the redundancy by integrating the files so that mulitiple copies of the same data are not stored.

eliminate /il'mineit/ (eliminates, eliminating, eliminated)

1. [verb] V n, v n from n

To eliminate you do not want or need, means to remove it completely (Formal) ( To eliminate 你不想要或不需要的， 意思是完全移除它)

If you think you may be allergic to a food or drink, eliminate it from your diet. (如果你认为， 你可能过敏对于某种食物或饮料，把它从你的食谱里消除掉。)

2. [v-passive] be v-ed from n, be v-ed

When a person or team is eliminated from a competition, they are defeated and so take no further part in the competition.

(当某人或某一团队从一次竟赛中被淘汰，他们是失败的，并且不能参加下一次竟赛。)

If you are eliminated in the show-jumping then you are out of the complete competition.

(如果你在跳跃中被淘汰了，接着，你将对所有竟赛出局。)

3. [verb] v n 

If someone says that they have eliminated an enemy, they mean that they have killed them.

(如果有人说，他们已经 eliminated了敌人，他们的意思是，他们已经杀死了敌人。)

By using the word 'eliminate', they are trying to make the action sound more positive than if they used the word 'kill'.

（通过使用单词'eliminate', 他们试图使动作听起来更积极一些，比起如果他们使用单词'kill'.）

He declared war on the government and urged right-wingers to eliminate opponents.

(他宣布，对政府战争，并敦促右翼分子消灭敌人。)

（相反，数据库方法试图消除冗余通过整合文件，以致于相同数据的多个副本不被存储。）

However, the database approach does not eliminate redundancy entirely, but controls the amount of redundancy inherent in the database.

inherent /inh'erənt/ [adj]  usu ADJ n 

The inherent qualities of something are the necessary and natural parts of it.  (事物的内在品质，是它必要的和自然的组成部分。)

Stress is an inherent part of dieting.(压力是节食的内在组成部分。)

... the dangers inherent in an outbreak of war. (内战爆发的危险。)

（无论如何，数据库方式不能完全消除冗余，但是可以控制数据库内部的冗余数量。）

Sometimes it is necessary to duplicate key data items to model relationship; at other times, it is duplicate some data items to improve performance.

The reasons for controlled duplication will become clearer as you read the next few chapters.

 

 

Data consistency
By eliminating or controlling redundancy, we reduce the risk of inconsistencies occurring.
（通过消除或者控制数据冗余，我们减少了不一致发生的风险。）
If a data item is stored only once in the database; any update to its value has to be performed only once
and the new value is available immediately to all users.
(在数据库中，数据项目如果仅存一次，对这个什的更新只能执行一次，新的更新值立即对所有用户都有用。)
If a data item is stored more than once and system is aware of this，
the system can ensure that all copies of the item are kept consistent.
(如果被存储的数据项多于一次，并且系统意识到这一点,系统可能确保所有该项目的副本保持一致。)
Unfortunately, many of today's DBMSs do not automatically ensure this type of consistency.
(不幸的是，今天，许多的DBMS不能自动确保这种类型的一致性。)
More information from the same amount of data
(从同样多的数据量提取更多的信息)

With the integration of the operation data, it may be possible for the organization to derive additional information
from the same data.
在操作数的整合下，从同一数据里，公司可能提取额外的信息。
derive/dir'aiv/ (derives deriving derived)
1. [verb] v n from n/-ing
If you derive something such as pleasure or benefit from a person or from something, you get it from them. (Formal)
如果你获得了某些事情，比如快乐和好处从一个人或者一些事情，你得到它从他们中间。
Mr. Ying is one of those happy people who derive pleasure from helping others.
银先是喜欢帮助人并且从中获得快乐人群中的一员。
2.[verb] be v-ed from n, v from n
If you say that something such as a word or feeling derives or is derived from something else,
you mean that it comes from that thing.
如果你说某些事情，诸如一个单词或工种感情，来源于某些其它事情，你的意思是，它来自那件事情。
Anna's strength is derived from her parents and her sisters...
The word Easter derives from Eostre, the pagan goddess of spring.
复活节这个单词来原于奥斯塔， 春天的女神。
For example, in the file-based system illustrated in Figure 1.5, the Contracts Department does not know who owns a leased property.
例如， 在图1.5中，基于文件系统的实例， 合同部门并不知道谁有租赁物业。

lease /li:s/ (leases leasing leased)
1. [N-count]  A lease is a legal agreement by which the owner of a building, a piece of land, or something such as a car allows someone else to use it for
a period of time in return for money.
He took up a 10 year lease on the house at Rossie Priory.
(他签约了10年的租期，在Rossie Priory)
2.[verb]V n, V n to n,  V n n;
If you lease property or something such as a car from someone or if they lease it to you, they allow you to use it in return for regular payments of money.
如果你租赁物业或者一些事情，诸如此类，来自某人的汽车，或者，如果他们把它租给你，他们允许你使用它，返回正规的付款。
He will need more grazing land and perhaps La Prade could lease him a few acres.
(他将需要更多的牧场， 也许拉.普拉德可能租给他一些。)
3. [Phrase] Phr after v  If you say that someone or something has been given a new lease of life, you are emphasizing that
they are much more likely or successful than they have been in the past.
如果说某人或者某事已经被赋予了新生，你是强调，他们是更可能或者更成功比起他们曾经。
The operation has given me a new lease of life.
操作给他的生命赋予了新生。

Similarly, Sale Department has asno knowledge of lease details.
相似，销售部门没有租赁明细。
When we integrate these file, the Contract Department has access to owner details and the Sales Department has access to lease details.
当我们整合这些文件时，合同部门录入用户的详细信息，销售部门录入租赁详细信息。

We may now be able to derive more information from the same amount of data. 
我们可以从相同的数据量导出更多的信息。