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集中式数据库系统Centralized Database System

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There are some real advantages in a centralized database system:
集中式数据库系统有一些优点:

1 .Consistency 一致性
It's easier to avoid multiple listing of individual pieces of data-and the possible inconsistency so introduced-if a central programming group has control of all data entry.
如果由一组中央程序控制所有数据项,则容易避免数据的多重目录一多重目录可能导致不一致性。

2.Retrievability 可检索性
  A central controlling group can make certain that all data entry follows a standard format and that the accessing of information also follows a standard and compatible format-all of which makes it very unlikely that any data will simply disappear。
控制程序可保证所有的数据项是标准格式的,对信息的访问也是标准的,而且是兼容格式,这样任何数据都不可能轻易丢失。

3. Data Independence 数据的独立性 
User applications should be immune to possible changes in data storage and access methods. This immunity is easier to achieve if a central programming group is in control of all internal-clever and conceptual-level storage and all user interfaces with the conceptual level. If the system gives all these important advantages, one might wonder if there is any alternative to the centralized system-that is,any reason to choose a decentralized system? There is one:
用户应用程序应不受数据存储和访问方式变化的影响,这种功能在中央程序控制所有内部级以及所有概念级数据存储和所有概念级用户接口时,比较容易实 现。既然提出了这些明显的优点,人们很自然地要问,除了集中式系统就没有其它方案了吗?即有理由选择分散式系统吗?理由有一个:  

A centralized system is efficient, but it may note responsive to user needs.This is particularly tureen large organizations- the worldwide meteorological network, for example. Data- gathering methods in the Himalayas, the equatorial jungles,and the North African desert are different in every possible way. It’s reasonable to believe that the best choices for the corresponding data storage and access structure sought to be just as different. A centralized databases stem would not accommodate such differences.
集中式系统虽然效率高,但它可能满足不了用户的要求,在大中型结构中,例如全球气象网络,尤其如此。喜马拉雅山、赤道丛林和北非大沙漠中的数据采 集方法就大不相同。因而必须承认,所选择的最佳数据存储方法和访问结构必然也是不同的。集中式数据系统必然不能解决这些差异文题。

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