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附件1：外文资料翻译译文 数据库简介 1数据库管理系统（DBMS）。众所周知，数据库是逻辑上相关的数据元的集合。这些数据元可以按不同的结构组织起来，以满足单位和个人的多种处理和检索的需要。数据库本身不是什么新鲜事早期的数据库记录在石头上或写在名册上，以及写入索引卡中。而现在，数据库普遍记录再可磁化的介质上，并且需要用计算机程序来执行必需的存储和检索操作。在后文中你将看到除了简单的以外，所有数据库中都有复杂的数据关系及其连接。处理与创建、访问以及维护数据库记录有关的复杂任务的系统软件包叫做数据库管理系统（DBMS）。DBMS软件包中的程序在数据库极其用户间建立了接口（这些用户可以是应用程序员、管理员以及其他需要信息和各种操作系统的人员）。DBMS可组织、处理和显示从数据库中选择的数据元。该功能使决策者可以搜索、试探和查询数据库的内容，从而对在正式报告中没有的、不再出现的且无计划的问题作出回答。这些问题最初可能是模糊的并且是定义不清的，但是人们可以浏览数据库直到获得问题的答案。也就是说DBMS将“管理”存储的数据项，并从公共数据库中汇集所需的数据项以回答那些非程序员的询问。在面向文件的系统中，需要特定信息的用户可以将他们的要求传送给程序员。该程序员在时间允许时，将编写一个或多个程序以提取数据和准备信息。但是，使用DBMS可为用户提供一种更快的、用户可以选择的通信方式。顺序的、直接的以及其它的文件处理方式常用于单个文件中数据的组织和构造，而DBMS能够访问和检索非关键记录字段的数据，即DBMS能够将几个大文件中逻辑相关的数据组织并连接在一起。逻辑结构。确定这些逻辑关系是数据管理者的任务，由数据定义语言完成。DBMS在存储、访问和检索操作过程中可选用以下逻辑结构技术：（1）表结构。在该逻辑方式中，记录通过指针链接在一起。指针是记录中的一个数据项，它指出另一个逻辑相关的记录的存储位置，例如，顾客主文件的记录将包含每个顾客的姓名和地址，而且该文件中的每个记录都由一个帐号标识。在记帐期间，顾客可在不同时间购买许多东西。公司保存一个发票文件以反映这些交易，这种情况下可使用表结构显示任一给定时间未支付的发票。顾客文件中的每个记录都将包含这样一个字段，该字段指向发票文件中该顾客的第一个发票的记录位置，该发票记录又依次与顾客的下一个发票记录相连，该链的最后一个发票记录由一个作为指针的特殊字符标识。（2）层次/树型结构。该逻辑方式中，数据单元的多级结构类似一棵“倒立”的树，该树的树根在顶部，而树枝向下延伸。在层次/树型结构中存在主-从关系，唯一的根数据下是从属的元或节点，而每个从属的元或节点又依次“拥有”一个或多个其他元（或者没有）。该结构中根下面的每个元或树枝都只有一个所有者，这样，一个顾客拥有一个发票，而发票又有从属项。在树型结构中，树枝不能连接。（3）网状结构。网状结构不像树型结构那样不允许树枝相连，它允许节点间多个方向连接，这样，每个节点都可能有几个所有者，而它又有可能拥有任意多个其他数据单元。数据管理软件允许从文件的任一记录开始提取该结构中的所需信息。（4）关系型结构。关系型结构由许多表组成，数据则以“关系”的形式存储在这些表中。例如，可以建立一些关系表将大学课程同该课程的教师以及上课地点连接起来。为了找到英语课的上课地点和教师名，先查询课程/教师关系得到名字，然后再查询课程/地点关系得到地点，当然，也可能有其他关系。这是一个相当新颖的数据库组织技术，将来有望得到广泛应用。物理结构。人们总是为了各自的目的，按逻辑方式设想或组织数据。这样，在一个具体应用中，记录R1和R2是逻辑相连且按顺序处理的，但是，在计算机系统中，这些一个应用中逻辑上邻接的记录，物理上完全可能不存储在一起。记录在介质和硬件中的物理结构不仅取决于所采用的I/O设备、存储设备及输入输出和存取技术，而且还取决于用户定义的R1和R2中数据的逻辑关系。例如，R1和R2可能是持有信用卡的顾客记录，而顾客要求每两周将货物运送到同一个城市的同一个街区，而从运输部门的管理者看，R1和R2是按地理位置组织的运输记录的顺序项。但是在A/R应用中，可找到R1和R2表示的顾客，并且可根据其完全不同的帐号处理他们的帐目。简言之，在许多计算机化的信息记录中，存储记录的物理位置用户是看不见的。2管理信息系统（MIS）。管理信息系统的概念已经拥许许多多的方式定义过，因为任何MIS的组织模型似乎都不同，所以各MIS的定义随应用范围的不同而变化就不奇怪了。按照我们的意思，一个MIS可定义为这样一个基于计算机的数据处理过程的网络系统，它是一个机构为了支持决策及其它必需的管理功能提供及时有效的信息而开发的，并且可按需要把人工操作过程结合在一起。尽管MIS模型不同，但其中大多数都认可横向管理结构。一个机构从纵向也可分成具有独立信息流特征和功能的多个模型，综合横向管理级和纵向特征产生了复杂的组织结构。这个结构的基础是数据库，该数据库原则上有内部和外部产生，用于过去、现在和将来事件相关的数据组成。MIS设计者的一个棘手的问题是分析支持决策所需的信息流。一把而言不同的管理者和各种职责的管理者所需的信息大多来自现有信息系统集，这些系统在MIS中可紧密地结合在一起，但是，更经常的情况是松散结合。3.数据库系统至关重要的一点是数据库应独立于任何一个具体的应用。传统的数据处理应用是数据相关的。COBOL语言程序包含详细描述数据格式和特性的文件说明和记录说明。用户可以改变数据库结构而不影响基于它的应用，例如改变应用的要求。一个简单的例子就是将ZIP代码从5位扩大到9位。按照COBOL语言程序的传统使用方法，各个使用该字段的COBOL应用程序不得不改变，并重新编译和测试。这些程序不能识别或访问已变化并含有一份数据结构说明书的文件，而这又可能反过来造成处理的混乱，除非这些变化已在设计中仔细考虑过。大多数数据库程序允许通过简单的修改ZIP代码段和数据项格式来改变数据库结构，在这种情况下，数据独立性使当前已存在的应用受到的破坏最小。用户可以继续工作甚至可以不管这个9位代码，该文件最终将转换成新的9位ZIP代码，如此容易的完成了修改更突出了数据独立性的重要性。数据完整性指数据库中数据的精确度、正确性或合法性，数据的完整性意味着保护数据不被非法修改或破坏。在大型联机数据库系统中，数据的完整性更为重要，并且还存在另外两个复杂的问题：一是不得不考虑多个用户同时访问数据库，例如，如果几千个旅行社代理人和航班订票员正同时访问一个数据库，且两个旅行社代理人预定了同机同号的机票，那么前面一个代理人的预定将丢失，在这种情况下，采用封锁记录或字段的技术就可以保护用户正在修改的记录免受其他用户访问；第二个问题与硬件、软件或者处理过程中人为错误有关，它包括使数据库始终保持完整性的数据库事务。数据库事务是一组视做整体的数据库修改工作，如一个旅行社代理人预定一个航班，预约就包括几个数据库的修改（即增加乘客的姓名和地址，并修改可用座位字段），这些修改组成了一个事务。只有当所有修改执行完毕后，才认为该数据库事务完成，否则不允许在进行其他任何修改。数据安全性指保护数据库不被越权或非法访问、修改，这通常涉及到一级或多级口令保护，而这些口令在数据字典中指明权限。例如，高级口令可允许用户读、写和修改数据库结构，而低级口令只允许用户从数据库读数。通常，审计跟踪记录着数据库修改的历史，可用来指明数据库破坏的时间和地点，也可用于文件的复原。附件2：外文原文DATA BASE MANAGEMENT SYSTEMS1.You know that a database is a collection of logically related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals. Theres nothing new about data basesearly ones were chiseled in stone, penned on scrolls, and written on index cards, But now data bases are commonly recorded on magnetized media, and programs are required to perform the necessary storage and retrieval operations.Youll see in the following pages that complex data relationships and linkages may be found in all but the simplest databases. The system software package that handles the difficult tasks associated with creating, accessing, and maintaining data base records is called a data base management system (DBMS). The programs in s DBMS package establish an interface between the database itself and the users of the database. (These users may be applications programmers, managers and others with information needs and various OS programs.)ADBMS can organize, process, and present selected data elements from the database. This capability enables decision makers to search, probe, and query data bade contents in order to extract answers to nonrecurring and unplanned questions that arent available in regular reports. These questions might initially be vague and poorly defined, but people can “browse” through the database until they have the needed information. In short, the DBMS will “manage” the stored data items and assemble the needed items from the common database in response to the queries of those who arent programmers. In a file-oriented system, users needing special information may communicate their needs to a programmer, who, when time permits, will write one or more programs to extract the data and prepare the information. The availability of a DBMS, however, offers users a much faster alternative communications path. Sequential, direct, and other file processing approaches are used to organize and structure data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquires for information. This means that the DBMS is able to structure and tie together the logically related data from several large files.Logical Structures. Identifying these logical relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations:(1). List structures. In this logical approach records are linked together by the use of pointers. A pointer is a data item in one record that identifies the storage location of another logically related record. Records in a customer master file, for example, will contain the name and address of each customer, and each record in this file is identified by an account number. During an accounting period, a customer may bye a number of items on different days. Thus, the company may maintain an invoice file to reflect these transactions. A list structure could be used in this situation to show the unpaid invoices at any given time. Each record in the customer file would contain a field that would point to the record location of the first invoice for that customer in the invoice file. This invoice record, in turn, would be linked to later invoices for the customer. The last invoice in the chain would be identified by the use of a special character as a pointer.(2). Hierarchical (tree) structures. In this logical approach, data units are structured in multiple levels that graphically resemble an “upside down” tree with the root at the top and the branches formed below. Theres a superior-subordinate elements of nodes, each of which, in turn, “own” one of more other elements (or none). Each element of branch in this structure below the root has only a single owner. Thus, a customer owns an invoice, and the invoice has subordinate items. The branches in a tree structure are not connected.(3). Network Strictures. Unlike the tree approach, which does not permit the connection of branches, the network structure permits the connection of the nodes in a multidirectional manner. Thus, each mode may have several owners and may, in turn, own any number of other data units. Data management software permits the extraction of the needed information from such a structure by beginning with any record in a file.(4). Relational structures. A relational structure is made up of many tables. The data are stored in the form of “relations” in these tables. For example, relation tables could be established to link a college course with the instructor of the course, and with the location of the English class, the course/instructor relation is searched to get the name (“Fit”), and the course/location relation is searched to get the class location. Many other relations are, of course, possible. This is a relatively new database structuring approach thats expected to be widely implemented in the future.Physical Structures. People visualize or structure data in logical ways for their own purposes. Thus, record R1 and R2may always be logically linked and processed in sequence in one particular application. However, in a computer system its quite possible that these records that are logically contiguous in one application are not physically stored together. Rather, the physical structure of the records in media and hardware may depend not only on the I/O and storage devices and techniques used, but also on the different logical relationships that users may assign to the data found in R1 and R2. For example, R1 and R2 may be records of credit customers who have shipments send to the same block in the same city every 2 weeks. From the shipping department managers perspective, then, R1 and R2 are sequential entries on a geographically organized shipping report. But in the A/R application, the customers represented by R1 and R2 may be identified, and their accounts may be processed, according to their account numbers which are widely separated. In short, then, the physical location of the stored records in many computer-based information systems is invisible to users.2.The management information system (MIS) concept has been defined in dozens of ways. Since one organizations model of an MIS is likely to differ from that of another, its not surprising that their MIS can be defined as a network of computer-based data processing procedure developed in an organization and integrated as necessary with manual and other procedures for the purpose of providing timely and effective information to support decision making and other necessary management functions.Although MIS models differ, most of them recognize the concepts. In addition to what might be termed the horizontal management structure. An organization is also divided vertically into different specialities and functions which require separate information flows. Combining the horizontal managerial levels with the vertical specialities produces the complex organizational structure. Underlying this structure is a database consisting, ideally, of internally and externally produced data relating to past, present and predicted future events.The formidable task of the MIS designer is to develop the information flow needed to support decisions making. Generally speaking, much of the information needed by managers who occupy different levels and who have different responsibilities is obtained from a collection of existing information systems (or subsystems).These systems may be tide together very closely in an MIS. More often, however, they are more loosely coupled. 3.An important point about database systems is that the database should exist independently of any of the specific applications. Traditional data processing applications are data dependent. COBOL programs contain file descriptions and record descriptions that carefully describe the format and characteristics of the data.Users should be able to change the structure of the database without affecting the applications that use it. For example, suppose that the requirements of your applications change. A simple example would be expanding ZIP codes from five digits to nine digits. In a traditional approach using COBOL programs, each individual COBOL application program that used that particular field would have to be changed, recompiled, and retested. The programs would be unable to recognize or access a file that had been changed and contained a new data description; this, in turn, might cause disruption in processing unless the changes were carefully planned.Most database programs provide the ability to change the database structure by simply changing the ZIP code field and the data-entry form. In this case, data independence allows for minimal disruption of current and existing applications. Users can continue to work and can even ignore the nine-digit code if they choose. Eventually, the file will be converted to the new nine-digit ZIP code, but the ease with which the changeover takes place emphasizes the importance of dada independence. Data integrity refers to the accuracy, correctness, or