计算机专业外文翻译原文-DBMS和MIS.doc

众所周知，数据库是逻辑上相关的数据元的汇集。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一早期的数据库凿在石头上，记在名册上，以及写在索引卡中。而现在，数据库普遍记录在可磁化的介质上，并且需要用计算机程序来执行必需的存储和检索操作。如下所述，所有数据库（最简单的除外）中都有复杂的数据关系及其链接。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与其用户间建立接口。（这些用户可以是应用程序员、管理员、及其他需要信息的人员和各种操作系统程序）。DBMS可组织、处理和表示从数据库中选出的数据元。该功能使决策者能搜索、探查和查询数据库的内容，从而对在正规报告中没有的、不再出现的且无法预料的问题作出回答。这些问题最初可能是模糊的并且（或者）是定义不恰当的，但是人们可以浏览数据库直到获得所需的信息。简言之，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应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。然而，DBMS的可用性为用户提供了一个更快的替代通信通道（如图7-1所示）。如果数据库管理系统提供一种方法来相互作用地进入和修改数据库，同时查询数据库，这种方法就为管理个人数据库创造了条件。但是，它不能自动留下一串查账行动，也不能在多用户组织中提供那种必要的控制。只有当一套应用程序为每一个数据进入和修改功能设定客户规格时，才有可能得到这些控制。当前，执行数据库系的一些功能的个人计算机软件一直很流行。个人计算机是供个人信息存储和处理而用。这些机器也广泛地被一些小企业、职业家如建筑师，医师、工程师、律师等等所使用。从使用意图的性质看，这些机器上的数据库系统没有正式数据库系统的一些要求。由于不需要数据分享，也不需要同时操作。软件也就不那么复杂。安全和整体维护也不那么重要，甚至没有随着数据容量变性能效率也不那么重要。事实上，数据库系统唯一重要的方面是数据独立。正如以前所述，数据独立是指在辅助存储器上，应用程序和用户询问不必知道数排的物理组织。这个方面的重要性，尤其对个人计算机用户来说，大大简化了数据库的使用。用户能够高层次地存储，存取和操纵数据，并且能够完全不受数据组织低层次细节的影响。在这里我们将不讨论一个特定个人计算机数据库管理系统软件包细节。我们将在下面总结一下个人计算机数据库软件系统的优缺点：最明显的积极方面是软件的用户友好型。一个事先不了解计算机知识的用户能够使用该系统来储存个人和职业数据，检索和执行有关处理。当然，用户应该使自己对软件质量感到满足，高质量的软件仗数据的出错率减少从而使数据投资 得到保护。对于完成应用的程序员而言，这个优点存在于支持这些系统所提供的在输入屏幕产生，输出报告产生方面的应用发展。主要消极点是缺少数据保护特征。除非被译成密码，数据不能被任何接触机器的人所存取。数据也能由于错误或被怀有恶意的人毁掉。以个人计算机为基础的许多系 统的第二个缺点是效率方面的缺点。如果数据发展到几千个记录，效率问题可能是一个难关。 由于数据容量的增长是一种发展趋势，所以应该考虑在较大的权器上获得相同或相容的软件。这是对用个人计算机数据库管理系统的最常见的错误概念之一：高综合和复杂的商业系统可以在dBASE，Paradox和其它数据库誉理系统中得以发展。但是，这些商业系统是由富有经验的程序设计员通过使用数据库管理系统专用的程序语言而建立的，这与建立和管理不是公司主要系统部分的个人文件的用户有所不同。1. 数据库的业务管理长期业务的目的是：在应用环境中模拟长期的、相互作用的数据库存取对话传统业务模式中关于短期业务的基本假设对于长期业务是不适用的。在存取数据前，当交易试图获得锁定时，传统模式业务的执行可能会引起长期等待。也可能引起大量工作丢失，当交易随着用户产生的障碍或系统失灵被放弃时。 业务模式的目的是提供严格的基础，在潜系统失灵的情况下，为了保持一套多个同时读写存取及数据库一致性，业务模式自动实行一个标准。在传统业务中采取的一致性标准是一种串行概念。在传统数据库系统中为自动并行控制，通过使用锁定而实行串行，并为了从系统失灵中自动恢复而联机。一个不能为实施自动数据库一致性而提供基础的业务不是一个真业务。确切地说，一个长期业务不必非采用串行作为它的一致标准，但是，必须有一些一致性的标准。2. 数据库的文本管理 在计算机辅助设计和软件工程的环境影响下，尽管对本文支持有许多建议，但对本文语义的意见不一致一直大大妨碍了数据库系统的文本支持。由于文件和数据库之间的差别，从直观上很清楚数据库系统的文本模式不可能与文件系统所采用的支持软件工程的文本模式同样简单。对于数据库来说，有必要不仅管理单个事务的文本（例如，一个软件模块，一份文件等等）而且也要管理许多事务（例如一个复合文件，一个用户手册等等）甚至还要管理数据库构图的文本。（例如一个表格和或一个类别，许多表格，许多类别）。 从广义上说，在文本的研究和发展方面有三个方向。第一，是参数文本的概念，即设计和任一种文本系统，其行为可能通过调节系统参数而改制。鉴于对文本的每一个单方而有许多似乎可行的选择这一事实，这可能是唯一可行的方法。 第二个方向是重访文本每一个方面的可一行的选择，目的在于将其中或者是不实用的或者有毛病的选择丢掉。第三个方向是对语义进行研究并执行描述一大批物体和数据库的构图。对于“管理信息系统”并没有一致的定义。一些作者喜欢用其他术语代替，例如：“信息处理系统”“信息与决策系统”“组织信息系统”，或者干脆将“信息系统”用组织内具有支持操作、管理、决策职能的计算机信息处理系统代替。这篇文章使用“管理信息系统”一词，是因为它是通俗易懂的，当涉及组织信息系统时也常用“信息系统”代替“管理信息系统”。一个管理信息系统的定义，通常被理解为：一种集成用户机器系统，为组织提供信息支持运作、管理、决策职能。该信息系统利用计算机硬件和软件；手工处理程序；模拟分析法计划、控制和决策；和数据库。事实上，它是一个集成系统并不意味着它是单一的，单块集成结构；相反，它意味着零件适合加入整体设计。内容定义如下：计算机为主的用户机器系统。理论上，管理信息系统可以脱离计算机上而存在，但是计算机的存在可以让管理信息系统可行。问题不是计算机是否被使用在管理信息系统中，而是信息的使用被计算机化的程度。用户机器系统的概念暗示了, 一些任务最好由人执行, 其他的最好由机器做。MIS的使用者是那些负责输入输入数据、指示系统或运用系统信息产品的人。因为许多问题，用户和计算机建立了一个联合系统，其结果通过一套在计算机和用户之间的相互作用得到。用户机器的相互作用是由用户连接在计算机上的输入-输出设备（通常是一个视觉显示终端）推动的。计算机可以使一台个人机器服务于一名用户或者一台大规模的机器为一定数量通过终端由通信线路连接的用户服务。用户输入-输出设备允许直接输入数据和紧接着输出结果。例如：一个人使用计算机交互的在金融理财上通过在终端键盘输入提交“如果什么，怎么办？”之类的问题，结果几秒钟后便被显示在屏幕上。MIS的计算机为主的用户机器特征影响系统开发商和系统用户的知识要求。“计算机为主”意味着管理信息系统的设计者必须拥有计算机和对处理有用的知识。“用户机器”的概念意味着系统设计者也应该了解人作为系统组成部分（信息处理器）的能力和人作为信息使用者的行为。信息系统的应用不应该要求用户成为计算机专家。但是，用户需要能够详细说明他们的信息要求；对计算机的一些理解、信息的本质，和对各种各样管理功能的利用将帮助用户完成任务。管理信息系统代表性地为集成组织信息处理提供依据。信息系统内部各自的应用则由不同批次的用户开发。如果没有集成的处理和机制，各自的应用也许无法协调一致和相容。在使用相同的数据时，数据项也许不同的被指定和不能兼容的横跨。当实际上一个单独的应用可以提供超过一个的更多的服务时，也许是分别的应用重复的发展了。用户想要通过使用从两种不同的应用中得到的数据来完成分析，也许会发现任务非常困难，有时甚至不可能。信息系统应用集成的第一步是一个整体信息系统计划。即使应用系统是一次一个的被执行，他们的设计可以由整体计划指导，确定他们怎么符合其他的工作。其实，信息系统被设计成为小型系统的一个飞行联盟。信息系统集成也通过标准，指南，和程序达到，被留作管理信息系统的功能之用。这种标准和程序的执行允许不同的应用分享数据，应付审核和控制条件，和被广泛用户共享。例如，一项应用也许被开发来操作特殊的小型计算机。集成的标准可能规定设备的选择与中央数据库一致。信息系统设计的这个趋势有利于将应用程序与用来支持它的数据分离。分开的数据库是一种机制，这种机制的数据项是通过横跨许多应用来集成和对不同的用户都可以始终一致的可利用。管理信息系统对于一个数据库的需要将在下面被谈论。术语“信息”和“数据”经常互换的被使用。然而，信息一般被定义为对接受者有意义或者有用的数据。因此数据项目是生产出信息的原料。数据库的潜在概念是，为了在处理中可以利用和具有恰当的特性，数据需要被管理。数据的管理包括软件和组织。创造软件和管理数据库就是数据库管理系统。当使用数据库的所有途径都是通过数据库管理系统被控制，所有应用都利用一个特殊数据项来存取被存放在唯一一个地方的相同的数据项。数据项的一个单独的更新，在所有方面都得到更新。用过数据库管理系统的集成要求数据库的一个中央集权。数据可能被放在一个中央计算机里或者被分散在几个计算机之中；最重要的要求是拥有一个组织功能来执行控制。对接受人来说只接收原始数据或者甚至是总结的数据都是不够的。数据通常需要被处理和被呈现出来，以结果指向所作的决定的方式。这样，数据项的处理建立于决策模型。例如，一项投资决定相对于新的资本支出也许根据一项政府支出决定模型被处理。决定模型可以在决策过程中被用来支持不同的阶段。“智能”模型可以用来寻找问题或者机会。模型可以被用来辨认和分析可能的解决方案。挑选模型，例如最优化模型可以被用来发现最想要的解决方案。换句话说，面对各种各样的决策情况需要多种的方法。下面是一些例子和可能被包含在一个管理信息系统中用来帮助分析和支持决策的模型的类型；一个全面的信息系统，决策者拥有一套有用的普通模型，可以应用于许多分析和决定的情况，还有一套非常特殊的模型应用于特别的决定。相似的模型可以用来计划和控制。选择的模型是管理信息系统的模型基础。在不同的情况下，当管理人员可以使用交互式的对话建立一个计划或者通过几个决定选择重复叙述，模型一般是最有效的。DATABASE MANAGEMENT SYSTEMS（DBMS）AND MANAGEMENT INFORMATION SYSTEM（MIS）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 individualsThere s nothing new about databasesearly ones1 were chiseled in stone，penned on scrolls，and written on index cardsBut now databases are commonly recorded on magnetizable media，and computer programs are required to perform the necessary storage and retrieval operationsYoull see in the following pages that complex data relationships and linkages may be found in all but the simplest databases2The system software package that handles the difficult tasks associated with creating，accessing，and maintaining database records is called a database management system（DBMS）The programs in a 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）A DBMS can organize，process，and present selected data elements from the databaseThis capability enables decision makers to search，probe，and query database contents in order to extract answers to nonrecurring and unplanned questions that arent available in regular reports3These questions might initially be vague and / or poorly defined，but people can“browse”through the database until they have the needed informationIn 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 programmersIn 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 information4The availability of a DBMS，however，offers users a much faster alternative communications path（see Fig. 7-1）If the DBMS provides a way to interactively and update the database, as well as interrogate it capability allows for managing personal data-Aces however, it does not automatically leave an audit trail of actions and does not provide the kinds of controla necessary in a multiuser organization. These-controls are only available when a set of application programs are customized for each data entry and updating function. Software for personal computers which perform me of the DBMS functions have been very popular arsenal computers were intended for use by individuals for personal information storage and process- These machines have also been used extensively small enterprises, professionals like doctors, acrylics, engineers, lawyers and so on By the nature of. intended usage, database systems on these machines except from several of the requirements of full doge database systemsSince data sharing is not：Tended, concurrent operations even less so, the) fewer can be less complex. Security and integrity7aintenance are de-emphasized or absent. As data-) limes will be small, performance efficiency Is also important. In fact, the only aspect of a database system that is Important is data Independence. Data-.dependence, as stated earlier. Means that applicant programs and user queries need not recognizantphysical organization of data on secondary storage. The importance of this aspect, particularly for the personal computer user, is that this greatly simplifies database usage. The user can store, access and manipulate data at a high level (close to the application) and be totally shielded from the low level (close to the machine) details of data organization. We will not discuss details of specific PC DBMS software packages hereLet us summarize in the following the strengths and weaknesses of personal computer data-base software systems： The most obvious positive factor is the user friendliness of the software. A user with no prior computer background would be able to use the system to store personal and professional data, retrieve and perform relayed processing. The user should, of course, satiety himself about the quality of software and the freedom from errors (bugs) so that invest-merits in data arc protected. For the programmer implementing applications with them, the advantage lies in the support for applications development in terms of input screen generations, output report generation etcoffered by theses stems The main negative point concerns absence of data protection featuresUnless encrypted, data cane accessed by whoever has access to the machine Data can be destroyed through mistakes or maliciousintent. The second weakness of manv of the PC-basedsystems is that of performance. If data volumes growup to a few thousands of records，performance couldbe a bottleneck For organization where growth in data volumesis expected, availability of, the same or compatiblesoftware on large machines should be considered.This is one of the most common misconceptionsabout database management systems that are used inpersonal computersThoroughly comprehensive andsophisticated business systems can be developed indBASh, Paradox and other DBMSsHowever, theyare created by experienced programmers using theDBMSs own programming language. That is not the same as users who create and manage personal filesthat are not part of the mainstream company systemTransaction Management of DatabaseThe objective of long-duration transactions is to model long-duration, interactive Database access sessions in application environmentsThe fundamental assumption about short-duration of transactions that underlies the traditional model of transactions is inappropriate for long-duration transactionsThe implementation of the traditional model of transactions may cause intolerably long waits when transactions aleph to acquire locks before accessing data, and may also cause a large amount of work to be lost when transactions are backed out in response to user-initiated aborts or system failure situations The objective of a transaction model is to pro-vide a rigorous basis for automatically enforcing criterion for database consistency for a set of multiple concurrent read and write accesses to the database in the presence of potential system failure situationsThe consistency criterion adopted for traditional transactions is the notion of scrializabilityScrializa-bility is enforced in conventional database systems through the use of locking for automatic concurrency control, and logging for automatic recovery from system failure situationsA transaction”that doesnt provide a basis for automatically enforcing data-base consistency is not really a transaction. To be sure, a long-duration transaction need not adopt seri-alizability as its consistency criterionHowever. there must be some consistcricv criterionVersion System Management of Database Despite a large number of proposals on version support in the context of computer aided design and software engineering, the absence of a consensus on version semantics has been a key impediment to version support in database systemsBecause of the differences between files and databases, it is intuitively clear that the model of versions in database systems cannot be as simple as that adopted in file systems to support software engineeringFor data-bases, it may be necessary to manage not only versions of single objects (e.g. a software module, document, but also versions of a collection of objects (e.g. a compound document, a user manual，etcand perhaps even versions of the schema of database (c.g. a table or a class, a collection of tables or classes) Broadly, there are three directions of research and development in versioningFirst is the notion of a parameterized versioning，that is, designing and implementing a versioning system whose behavior may be tailored by adjusting system parameters This may be the only viable approach, in view of the fact that there are various plausible choices for virtually every single aspect of versioningThe second is to revisit these plausible choices for every aspect of versioning, with the view to discarding some of themes either impractical or flawed. The third is the investigation into the semantics and implementation of versioning collections of objects and of versioning the database sche There is no consensus of the definition of the term management information system. Some writers prefer alternative terminology such as information processing system, information and decision system, organizational information system, or simply information system to refer to the computer-based information processing system which supports the operations, management, and decision-making functions of an organization. This text uses “MIS” because it is descriptive and generally understood; it also frequently uses “information system” instead of “MIS” to refer to an organizational information system.2、A definition of a management information system, as the term is generally understood, is an integrated, user-machine system for providing information to support operations, management, and decision-making functions in an organization. The system utilizes computer hardware and software; manual procedures; models for analysis planning, control and decision making; and a database. The fact that it is an integrated system does not mean that it is a single, monolithic structure; rather, it means that the parts fit into an overall design. The elements of the definition are highlighted below. Computer-based user-machine system3、Conceptually, a management information can exist without computer, but it is the power of the computer which makes MIS feasible. The question is not whether computers should be used in management information system, but the extent to which information use should be computerized. The concept of a user-machine system implies that some tasks are best performed by humans, while others are best done by machine. The user of an MIS is any person responsible for entering input data, instructing the system, or utilizing the information output of the system. For many problems, the user and the computer form a combined system with results obtained through a set of interactions between the computer and the user.4、User-machine interaction is facilitated by operation in which the users input-output device( usually a visual display terminal) is connected to the computer. The computer can be a personal computer serving only one user or a large computer that serves a number of users through terminals connected by communication lines. The user input-output device permits direct input of data and immediate output of results. For instance, a person using the computer interactively in financial planning poses “what if” questions by entering input at the terminal keyboard; the results are displayed on the screen in a few second.5、The computer-based user-machine characteristics of an MIS affect the knowledge requirements of both system developer and system user. “computer-based” means that the designer of a management information system must have a knowledge of computers and of their use in processing. The “user-machine” concept means the system designer should also understand the capabilities of humans as system components (as information processors) and the behavior of humans as users of information.6、Information system applications should not require users to be computer experts. However, users need to be able to specify their information requirements; some understanding of computers, the nature of information, and its use in various management function aids users in this task.Integrated system集成系统7、Management information system typically provide the basis for integration of organizational information processing. Individual applications within information systems are developed for and by diverse sets of users. If there are no integrating processes and mechanisms, the individual applications may be inconsistent and incompatible. Data item may be specified differently and may not be compatible across applications that use the same data. There may be redundant development of separate applications when actually a single application could serve more than one need. A user wanting to perform analysis using data from two different applications may find the task very difficult and sometimes impossible.8、The first step in integration of information system applications is an overall information system plan. Even though application systems are implemented one at a time, their design can be guided by the overall plan, which determines how they fit in with other functions. In essence, the information system is designed as a planed federation of small systems.9、Information system integration is also achieved through standards, guidelines, and procedures set by the MIS function. The enforcement of such standards and procedures permit diverse applications to share data, meet audit and control requirements, and be shares by multiple users. For instance, an application may be developed to run on a particular small computer. Standards for integration may dictate that the equipment selected be compatible with the centralized database. The trend in information system design is toward separate application