数据库相关毕业设计外文翻译.doc

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 theDBMS's 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 Database   The 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 processing form the data used to support it. The separate database is the mechanism by which data items are integrated across many applications and made consistently available to a variety of users. The need for a database in MIS is discussed below.Need for a database 10、 The term “information” and “data” are frequently used interchangeably; However, information is generally defined as data that is meaningful or useful to the recipient. Data items are therefore the raw material for producing information.11、The underlying concept of a database is that data needs to be managed in order to be available for processing and have appropriate quality. This data management includes both software and organization. The software to create and manage a database is a database management system.12、When all access to any use of database is controlled through a database management system, all applications utilizing a particular data item access the same data item which is stored in only one place. A single updating of the data item updates it for all uses. Integration through a database management system requires a central authority for the database. The data can be stored in one central computer or dispersed among several computers; the overriding requirement is that there be an organizational function to exercise control.Utilization of Models 13、It is usually insufficient for human recipients to receive only raw data or even summarized data. Data usually needs to be processed and presented in such a way that the result is directe