文献综述和外文翻译的撰写要求

通知：（4.30-5.4）完成毕业设计
(5.7-5.11)提交论文
4.30-5.11之间自己带上电脑来演示系统并讲解功能等。对于文献综述和外文资料翻译情况的要求如下：

一、文献综述

1.查阅中外文献资料，所查阅的中外文献资料不得少于16篇（其中中文文献不得少于14篇，外文文献不得少于2篇）。


2.文献综述

　含本选题国内外研究现状、研究主要成果、发展趋势、存在问题等内容，字数不少于5000字，力求内容切题，具综合归纳性。格式按论文要求格式撰写。



二、外文资料翻译（不少于3000外文印刷字符）

如：
1．所译外文资料：
①作者：Abraham Silberschatz , Henry E Korth , S.Sudarshan
②书名：DATABASE SYSTEM CONCEPTS
③出 版 社（或刊物名称）：China Machine Press
④出版时间（或刊号）：1999
⑤所译页码：1-4

A database-management system (DBMS) consists of a collection of interrelated data and a set of rograms to access those data. The collection of data usually referred to as the database, contains information about one particular enterprise. The primary goal of a DAMS is to provide an environment that is both convenient and efficient to use in retrieving and efficient to use in retrieving and storing database information.
Database systems are disigned to manage large bodies of information. The management of data involves both the difinition of structures for the storage of information and the provision of mechanisms for the manipulation of information. In addition, the database system must provide for the safety of the information stored, despite system crashes or attempts at unauthorized access. If data are to be shared among several users, the system must avoid possible anomalous results.
The inportance of information in must organizations – which determines the value of the database – has led to the development of a large body of concepts and techniques for the efficient management of data. In this chapter, we present a brief introduction to the principles of database systems.
1.1 Purpose of Database Systems
Consider part of a savings-bank enterprise that keeps information about all customers and savings accountsl. One way to keep the information on a computer is to store it in permanent system files. To allow users to manipulate the information, the system has a number of application programs that manipulate the files, including.
?A program to debit or credit an account
?A program to add a new account
?A program to find the balance of an account
?A program to generate monthly statements
These application programs have been written by system programmers in response to the needs of the bank organization.
New application programs are added to the system as the need arises. For example, suppose that new government regulations allow the saving bank to offer checking accounts. As a result, new permanent files are cre

ated that contain information about all the checking accounts maintained in the bank, and new application programs may need to be written to deal with situations that do not arise in savings accounts, such as handling overdrafts. Thus, as time goes by, more files and more application programs are added to the system.
The typical file-processing system just described is supported by a conventional operating system. Permanent record are stored in various files, and different application programs are written to extractrecords from, and to add records to, the appropriate files. Before the advent of DBMSs, organizations typically stored information using such systems.
Keeping organizational information in a file-processing system has a number of major disadvantages.
?Data redundancy and inconsistency. Since the files and application programs are created by different programmers over a long period, the various files are likely to have different formats and the programs may be written in several programming languages. Moreover, the same information may be duplicated in several places (files). For example, the address and telephone number of a particular customer may appear in file that consists of savings-account records and in a file that consists of checking-account records. This redundancy leads to higher storage and access cost. In addition, it may lead to data inconsistency; that is, the various copies of the same data may no longer agree. For example, a changed coustomer address may be reflected in savings-account records but not elsewhere in the system.
?Difficulty in accessing data. Suppose that one of the bank officers needs to find out the names of all customers who live within the city’s 78733 zip code. The officer asks the data-processing department to generate such a list. Because this request was not anticipated when the original system was designed, there is no application program on hand to meet it. There is, however, an application program to generate the list of all customers. The bank officer has now two choices: Either obtain the list of all customers and have the needed information extracted manually, or ask the data-processing department to have a system programmer write the necessary application program. Both alternatives are obviously unsatisfactory. Suppose that such a program is written, and that, several days later, the same officer needs to trim that list to include only those customers who have an account balance of $ 10,000 or more. As expected, a program to generate such a list does not exist. Again, the officer has the preceding two options, neither of which is satisfactory.
The point here is that conventional file-processing environments do not allow needed data to be retrieved in a convenient and efficient manner. More responsive data-retrieval systems must be developed for general use.
?Data isolation. Because data are scattered in various files, and files may be in different formats, it is difficult to write n

ew application programs to retrieve the appropriate data.
?Integrity problems. The data values stored in the database must satisfy certain types of consistency constraints. For example, the balance of a bank account may never fall below a prescribed amount (say $25). Developers enforce these constraints in the system by adding appropriate code in the various application programs. However, when new constraints are added, it is difficult to change the programs to enforce them. The problem is compouned when constraints involve several data items from differents files.
?Atomicity problems. A computer system, like any other mechanical or electrical device, is subject to failure. In mary applications, it is crucial to ensure that, once a failure has occurred and has been detected, the data are restored to the consistent state that existed prior to the failure. Consider a porogram to transfer $50 from account A to B. If a system failure occurs during the execution of the program, it is possible that the $50 was removed from account A but was not credited to account B, resulting in an inconsistent database state. Clearly, it is essential to database consistency that either both the credit and debit occur, or that neither occur. That is, the funds transfer must be atomic – it must happen in its entorety or not all. It is difficult to ensure this property in a conventional file-processing system.
?Concurrent-access anomalies. So that the overall performance of the system is improved and a faster response time is possible, many systems allow multiple users to update the data simultaneously. In such an environment, interaction of concurrent updates may result in inconsistent data. Consider bank account A, containing $500. If two customers withdraw funds (day $50 and $ 100 respectively) from account A at about the same time, the result of the concurrent executions may leave the account in an incorrect (or inconsistent) state. Suppose that the programs executing on behalf of each withdrawal read the old balance, reduce that value by the amount being withdrawn, and wirte the result back. If the two programs run concurrently, they may both read the value $500, and writes back $450 and $400, respectively. Depending on which one writes the value last, the account may contain either $450 or $400, rather than the correct value of $350. To guard against this possibility, the system must maintain some form of supervision. Because data may be accessed by many different application programs that have not been coordinated previously, however, supervision is difficult to provide.
?Security problems. Not every user of the database system should be able to access all the data. For example, in a banking system, p0ayroll personnel need to see only that part of the database that has information about the various bank employees. They do not need access to information about customer accounts. Since application programs are added to the system in an ad hocmanner, it is diff

icult to enforce such security constraints.
These difficulties, among others, have prompted the development of DBMSs. In what follows, we shall see the concepts and algorithms that have been developed for database systems to solve the problems mentioned. In most of this book, we use a bank enterprise as a running example of a typical data-rpocessing application found in a corporation. A typical data- processing application stores a large number of records, each of which is fairly sipmle and small.

2．译成中文：

数据库管理系统（DBMS）由一个互相关联的数据的集合和一组用民访问这些数据的程序组成，这个数据集合通常称作数据库，其中包含了关于某个企业的信息。DBMS的基本目标是要提供一个可以方便地、有效地存取数据库信息的环境。
设计数据库系统的目的是为了管理大量信息。对数据的管理既涉及到信息存储结构的定义，又涉及信息操作机制的提供。另外，数据库系统还必须提供所存储信息的安全性保证，即使在系统崩溃或有人企图越权访问时也应保障信息的安全性。如果数据将被多用户共享，那么系统还必须设法避免可能产生的异常结果。
对大多数组织而言，信息都非常重要，这决定了数据库的价值，并使得大量的用于有效管理数据的概念、技术得到发展。本章将简要介绍数据库系统的基本原理。

1.1数据库系统的目的

假设储蓄银行的某个部门需要保存所有客户及储蓄帐户的信息，在计算机上保存这些信息的一种方法是将它们存放在永久性系统文件中。为了使用户对信息进行操作，系统中应有一些对文件进行操作的应用程序，包括：
?处理某帐户的借/贷程序。
?创建新帐户的程序。
?查询帐户余额的程序。
?产生每月财务报告的程序。
这些应用程序是由系统程序员根据银行的需求编写的。
随着需求的增长，新的应用程序加入到系统中来。例如，如果政府颁布新条例允许储蓄银行开设支票帐户，这时银行就需要创建新的永久文件来存放银行所维护的所有支票帐户的信息，同时还可能需要编写新的应用程序来处理那些在储蓄帐户里不会出现的情况（例如：透支）。因此，随着时间的推移，越来越多的文件和应用程序加入到系统中。
以上所描述的典型的文件处理系统是传统的操作系统所能以持的。永久记录被存储在多个不同的文件中，人们编写不同的应用程序来将记录从适当的文件中取出或加入到适当的文件中。在DBMS出现以前，各个组织通常都采用这样的系统来存储信息。
在文件处理系统中存储信息的主要弊端包括：
?数据的冗余和不一致。由于文件和程序是很长一段时间内由不同的程序员创建的，因此不同文件可能采用不同

格式，不同程序可能采用不同语言。此外，相同的信息可能在几个地方（文件）重复存储。例如，某个客户的地址和电话号码可能既在由储蓄帐户记录组成的文件中出现，也可能导致数据不一致，即同一数据的不同副本不一致。例如，某个客户地址的更改可能只在储蓄帐户记录中得到反映而在系统的其他地方却没有得到反映。
?数据访问困难。假设银行的某个高级职员想要找出所有居住地邮编为78733的客户的姓名，这时他会要求数据处理部门生成这样的一个列表。由于在最初的系统设计时并未预料到会有这样的需求，所以没有现成的应用程序去满足此需求。但是，系统中邓有一个产生所有客户列表的应用程序，这时该高级职员有两种选择：一种是取得所有客户的列表并从中手工提取所需信息；另一种是要求数据处理部门让某个系统程序员编写相应的应用程序。这两种方案显然都不太令人满意，假设编写了相应的程序，几天后这个高级职员可能又需要将该列表减少到只列出帐户余额不少于S10000的那些客户，可以预见，产生这样一个列表的程序又不存在，这个高级职员就又再一次面临着前面那两种不尽人意的选择。
这里要着重指出的是，传统的文件处理环境不能支持以一种方便而有效的方式去获得所需数据，需要开发通用的、能过变化的需求作出更快反应的数据检索系统。
?数据孤立。由于数据分散在不同文件中，这些文件又可能具有不同的格式，因而编写新的且检索恰当数据的应用程序是很困难的。
?完整性问题。数据库中所存储数据的值必须满足某种一致性约束。例如，银行帐户的余额永远不会低于某个预定的值（如：$25）。开发者通过在不同应用程序中加入适当的代码来体现系统中的这些约束。然而，当新的约束加入时，很难通过修改程序来体现这些新的约束，尤其是当约束涉及不同文件中的多个数据项时，问题就变得更加复杂了。
?原子性问题。如同其他的机械或电子设备一样，计算机系统也常常会发生故障，一旦故障发生并被检测到，数据就应恢复到与故障发生前一致的状态。对许多应用来说，这样的功能是至关重要的。让我们看看把A帐户的$50转入B帐户这样一个例子。假设在程序的执行过程中发生了系统故障，很可能A帐户上减去的$50还没来得及存入B帐户，这就造成了数据库状态的不一致。显然，为了保证数据库状态的一致性，这里的借、贷两个操作必须是要么都发生要么都不发生，也就是说，转帐这个操作必须是原子的——它要么全部发生要么根本不发生。在传统的文件处理系统中，这样的性能难以得到保证。
?并发

访问异常。为了提高系统的总体性能以及加快响应速度，许多系统允许多个用户同进更新数据。在这样的环境中，并发更新操作相到影响，可能就会导致数据的不一致。设A帐户中有$500，假如两个客户几乎同时从A帐户取示，分别取出$500和$100，这样的并发执行就可能使帐户外于一种错误的或者说不一致的状态。假设每个取款操作对应执行的程序是读取帐户余额，在其上减去取款的金额，然后将结果写回。如果两次取款的程序并发执行，可能它们读到一余额后写回结果而定，而实际上这两种结果都是错的，正确的值应该是350。由此可见，为了消除这种情况发生的可能性，系统必须进行某种形式的管理。但是，由于数据可能被多个不同应用程序访问，这些程序相互间事先又没有协调管理，因而很难进行。
安全性问题。并非数据库系统的所有用户都可以访问所在数据。例如在银行系统中，工资发放人员只面要看到数据库中关于银行员工的那部分信息，他们不需要访问关于客户帐户的信息。由于应用程序总是即兴加入到系统中来，这样的安全性约束难以实现。
以上问题以及还未提到的一些其他问题，回速了DBMS的发展，接下来看一看数据库系统为了解决止述问题而提出的概念和算法。本书的大部分篇幅在讨论企业常见的数据处理应用时总以银行为实例。典型而数据处理应用中存储记录的数量总是很大，而每一条记录即小又简单。