【文献翻译／第一页】数据库系统简介1An Introduction to ...

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翻译：数据库系统简介（1）
数据库管理系统（DBMS）是由一组
相互关联的数据和访问这些数据的一组程序。数据库是通过集中数据和最小化冗余数据（data redundancy ）来高效地为许多应用程序服务的数据集合。数据库管理系统的主要目标是提供一个在检索和存储数据库信息时既方便又高效的环境。
数据库系统设计用于管理大量信息。数据管理包括定义存储信息的结构和提供存储信息的机制
尽管系统必须避免可能的异常结果，但／并对存储的信息进行操作。
信息在大多数组织中的重要性决定了数据库的价值，这导致了数据库概念和技术的大量发展，也导致了数据高效管理概念和技术的大量发展。
典型的文件处理系统由传统的操作系统支持。永久记录存储在各种文件中，并编写不同的应用程序来从适当的文件中提取记录并向其中添加记录。在DBMS出现之前，组织通常使用此类系统存储信息。
在文件处理系统中保存组织信息有许多主要缺点。
数据冗余和不一致。数据冗余是指多个数据文件中存在重复数据。因为文件和应用程序是由
不同的程序员在很长一段时间内不同的文件可能有不同的格式，程序可能用几种编程语言编写
信息可能在多个位置（文件）重复。这种冗余会导致更高的存储和访问成本。此外，可能导致数据不一致；也就是说，相同数据的不同副本可能不再一致。
访问数据的困难。这里的要点是
文件处理环境不允许以方便和高效的方式检索所需的数据。必须为通用开发响应性更强的数据检索系统。
完整性问题。存储在数据库中的数据值必须满足某些类型的一致性约束。开发人员强制
通过在各种应用程序中添加适当的代码，在系统中添加约束。但是，当添加新的约束时，很难更改程序以强制执行它们。问题是
当约束涉及来自不同文件的多个数据项时，会变得复杂。
原子性问题。计算机系统和任何其他机械或电气设备一样，都会发生故障。在许多应用程序中，确保一旦发生故障并检测到数据，就将数据恢复到故障之前存在的一致状态。考虑一个程序从帐户A转移50美元到B。IFA系统故障在程序执行期间发生，50美元可能已从帐户A中删除，但未贷记到帐户B中，从而导致数据库状态一致。显然，要保持数据库一致性，必须同时发生贷记和借记，或者两者都不发生。也就是说，必须进行资金转账（转移）
tp：不确定的词：credit 好像是类似debit借方相对贷方人的记录帐
原文：An Introduction to Database Systems 1
A Database Management System(DBMS consists of a collection of
interrelated data and a set ofprograms to access those data.A database is acollection of data organized to server many applications efficiently by centralizing thedata and minimizing redundant data.The primary goal o f a DBMS is to provide anenvironment that is both convenient and efficient to use in retrieving and storing databaseinfor mat io n.
Database systems are designed to manage large bodies of information.Themanagement of data involves both the definition of structures for the storage ofinformation and the provision of mechanisms for the
manipulation of information stored,despite system must avoid possible anomalousre s ults.
The important of information in most organizations,which determines the value ofthe database,has led to the development of a large body ofconcepts and techniques forthe database,has led to the development of a large body ofconcepts and techniques forthe efficient management ofdata.
The typical file-processing system is supported by a conventional operating system.Permanent records are stored in various files,and different application programs arewritten to extract records from,and to add records to, the appropriate file s.Before theadvent o f DBMS s,organizations typ ically stored information using such systems.
Keeping organizational information in a file-processing system has a number ofmajor disadvantages.
Data redundancy and inconsistency.Data redundancy is the presence of duplicatedata in multiple data files.S ince the files and application programs are created by
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different programmers over a long period, the various files are likely to have differentformats and the programs may be written in several programming languages.Moreover,the same
information may be duplicated in several places (files.This redundancy leads tohigher storage and access cost. In addition, it may lead to data inconsistency; that is, thevarious copies of the same data may no longer agree.
Difficulty in accessing data.The point here is that conventional
file-processing environments do not allow needed data to be retrieved in aconvenient and efficient manner.More responsive data-retrieval systems must bedeveloped for general use.
Integrity problems.The data values stored in the database must satisfy certain typesofconsistency constrains.Developers enforce the
constraints in the system by adding appropriate code in the various applicationprograms.However,when new constraints are added, it is difficult to change theprograms to enforce them.The problem is
compounded when constraints involve several data items from different files.
Atomicity problems.A computer system, like any other mechanical or electricaldevice, is subject to failure. In many applications, it is crucial to ensure that,once afailure has occurred and has been detected, the data are restored to the consistent statethat existed prior to the failure.Consider a program to transfer$50 from account A to B.Ifa system failure occurs during the execution of the program, it is possible that the$50was removed from account A but was not credited to account B,resulting in aninconsistent database state.Clearly, it is essential to database consistency that either boththe credit and debit occur,or that neither occurs.That is, the funds transfer must be