计算机专业外文翻译原文 数据库管理系统介绍

1、 计算机专业外文翻译+原文-数 据库管理系统介绍扬州大学计算机专业毕业设计(外文翻译) 外文资料 Database Management SystemsA database (sometimes spelled data base) is also called an electronic database , referring to any collection of data, or information, that is specially organized for rapid search and retrieval by a computer. Databases are st

2、ructured to facilitate the storage, retrieval , modification, and deletion of data in conjunction with various data-processing operations .Databases can be stored on magnetic disk or tape, optical disk, or some other secondary storage device. A database consists of a file or a set of files. The info

3、rmation in these files may be broken down into records, each of which consists of one or more fields. Fields are the basic units of data storage , and each field typically contains information pertaining to one aspect or attribute of the entity described by the database . Using keywords and various

4、sorting commands, users can rapidly 1 扬州大学计算机专业毕业设计(外文翻译) search , rearrange, group, and select the fields in many records to retrieve or create reports on particular aggregate of data. Complex data relationships and linkages may be found in all but the simplest databases .The system software packag

5、e 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 prog

6、rammers, managers and others with information needs, and various OS programs.) A DBMS can organize, process, and present selected data elements form the database. This capability enables decision makers to search, probe, and query database contents in order to extract answers to nonrecurring and unp

7、lanned questions that arent available in regular reports. These questions might initially be vague and/or poorly 2 扬州大学计算机专业毕业设计(外文翻译) 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

8、 needed items from the common database in response to the queries of those who arent programmers. A database management system (DBMS) is composed of three major parts:(1)a storage subsystem that stores and retrieves data in files;(2) a modeling and manipulation subsystem that provides the means with

9、 which to organize the data and to add , delete, maintain, and update the data;(3)and an interface between the DBMS and its users. Several major trends are emerging that enhance the value and usefulness of database management systems; Managers: who require more up-to-data information to make effecti

10、ve decision Customers: who demand increasingly sophisticated information services and more current information about the status of their 3 扬州大学计算机专业毕业设计(外文翻译) orders, invoices, and accounts. Users: who find that they can develop custom applications with database systems in a fraction of the time it

11、takes to use traditional programming languages. Organizations : that discover information has a strategic value; they utilize their database systems to gain an edge over their competitors. The Database Model A data model describes a way to structure and manipulate the data in a database. The structu

12、ral part of the model specifies how data should be represented(such as tree, tables, and so on ).The manipulative part of the model specifies the operation with which to add, delete, display, maintain, print, search, select, sort and update the data. Hierarchical Model The first database management

13、systems used a hierarchical model-that is-they arranged records into a tree structure. Some records are root records 4 扬州大学计算机专业毕业设计(外文翻译) and all others have unique parent records. The structure of the tree is designed to reflect the order in which the data will be used that is ,the record at the r

14、oot of a tree will be accessed first, then records one level below the root ,and so on. The hierarchical model was developed because hierarchical relationships are commonly found in business applications. As you have known, an organization char often describes a hierarchical relationship: top manage

15、ment is at the highest level, middle management at lower levels, and operational employees at the lowest levels. Note that within a strict hierarchy, each level of management may have many employees or levels of employees beneath it, but each employee has only one manager. Hierarchical data are char

16、acterized by this one-to-many relationship among data. In the hierarchical approach, each relationship must be explicitly defined when the database is created. Each record in a hierarchical database can contain only one key field and only 5 扬州大学计算机专业毕业设计(外文翻译) one relationship is allowed between any

17、 two fields. This can create a problem because data do not always conform to such a strict hierarchy. Relational Model A major breakthrough in database research occurred in 1970 when E. F. Codd proposed a fundamentally different approach to database management called relational model ,which uses a t

18、able as its data structure. The relational database is the most widely used database structure. Data is organized into related tables. Each table is made up of rows called and columns called fields. Each record contains fields of data about some specific item. For example, in a table containing info

19、rmation on employees, a record would contain fields of data such as a persons last name ,first name ,and street address. Structured query language(SQL)is a query language for manipulating data in a relational database .It is nonprocedural or declarative, in 6 扬州大学计算机专业毕业设计(外文翻译) which the user need

20、only specify an English-like description that specifies the operation and the described record or combination of records. A query optimizer translates the description into a procedure to perform the database manipulation. Network Model The network model creates relationships among data through a lin

21、ked-list structure in which subordinate records can be linked to more than one parent record. This approach combines records with links, which are called pointers. The pointers are addresses that indicate the location of a record. With the network approach, a subordinate record can be linked to a ke

22、y record and at the same time itself be a key record linked to other sets of subordinate records. The network mode historically has had a performance advantage over other database models. Today , such performance characteristics are only important in high-volume ,high-speed transaction processing su

23、ch as automatic teller machine 7 扬州大学计算机专业毕业设计(外文翻译) networks or airline reservation system. Both hierarchical and network databases are application specific. If a new application is developed ,maintaining the consistency of databases in different applications can be very difficult. For example, sup

24、pose a new pension application is developed .The data are the same, but a new database must be created. Object Model The newest approach to database management uses an object model , in which records are represented by entities called objects that can both store data and provide methods or procedure

25、s to perform specific tasks. The query language used for the object model is the same object-oriented programming language used to develop the database application .This can create problems because there is no simple , uniform query language such as SQL . The object model is relatively new, and only

26、 a few examples of object-oriented database exist. It has attracted 8 扬州大学计算机专业毕业设计(外文翻译) attention because developers who choose an object-oriented programming language want a database based on an object-oriented model. Distributed Database Similarly , a distributed database is one in which differe

27、nt parts of the database reside on physically separated computers . One goal of distributed databases is the access of information without regard to where the data might be stored. Keeping in mind that once the users and their data are separated , the communication and networking concepts come into

28、play . Distributed databases require software that resides partially in the larger computer. This software bridges the gap between personal and large computers and resolves the problems of incompatible data formats. Ideally, it would make the mainframe databases appear to be large libraries of infor

29、mation, with most of the processing accomplished on the personal computer. A drawback to some distributed systems is 9 扬州大学计算机专业毕业设计(外文翻译) that they are often based on what is called a mainframe-entire model , in which the larger host computer is seen as the master and the terminal or personal compu

30、ter is seen as a slave. There are some advantages to this approach . With databases under centralized control , many of the problems of data integrity that we mentioned earlier are solved . But todays personal computers, departmental computers, and distributed and processing their require computers

31、applications to communicate with each other on a more equal or peer-to-peer basis. In a database, the client/server model provides the framework for distributing databases. One way to take advantage of many connected computers running database applications is to distribute the application into coope

32、rating parts that are independent of one anther. A client is an end user or computer program that requests resources across a network. A server is a computer running software that 10 扬州大学计算机专业毕业设计(外文翻译) fulfills those requests across a network . When the resources are data in a database ,the client/

33、server model provides the framework for distributing database. A file serve is software that provides access to files across a network. A dedicated file server is a single computer dedicated to being a file server. This is useful ,for example ,if the files are large and require fast access .In such

34、cases, a minicomputer or mainframe would be used as a file server. A distributed file server spreads the files around on individual computers instead of placing them on one dedicated computer. Advantages of the latter server include the ability to store and retrieve files on other computers and the

35、elimination of duplicate files on each computer. A major disadvantage , however, is that individual read/write requests are being moved across the network and problems can arise when updating files. Suppose a user requests a record from a file and changes it while another 11 扬州大学计算机专业毕业设计(外文翻译) user

36、 requests the same record and changes it too. The solution to this problems called record locking, which means that the first request makes others requests wait until the first request is satisfied . Other users may be able to read the record, but they will not be able to change it . A database serv

37、er is software that services requests to a database across a network. For example, suppose a user types in a query for data on his or her personal computer . If the application is designed with the client/server model in mind ,the query language part on the personal computer simple sends the query a

38、cross the network to the database server and requests to be notified when the data are found. Examples of distributed database systems can be found in the engineering world. Suns Network Filing System(NFS),for example, is used in computer-aided engineering applications to distribute data among the h

39、ard disks in a network of Sun workstation. 12 扬州大学计算机专业毕业设计(外文翻译) Distributing databases is an evolutionary step because it is logical that data should exist at the location where they are being used . Departmental computers within a large corporation ,for example, should have data reside locally ,

40、yet those data should be accessible by authorized corporate management when they want to consolidate departmental data . DBMS software will protect the security and integrity of the database , and the distributed database will appear to its users as no different from the non-distributed database . I

41、n this information age, the data server has become the heart of a company. This one piece of software controls the rhythm of most organizations and is used to pump information lifeblood through the arteries of the network. Because of the critical nature of this application, the data server is also t

42、he one of the most popular targets for hackers. If a hacker owns this application, he can cause the companys heart to suffer a fatal arrest. Ironically, although most users are now 13 扬州大学计算机专业毕业设计(外文翻译) aware of hackers, they still do not realize how susceptible their database servers are to hack a

43、ttacks. Thus, this article presents a description of the primary methods of attacking database servers (also known as SQL servers) and shows you how to protect yourself from these attacks. You should note this information is not new. Many technical white papers go into great detail about how to perf

44、orm SQL attacks, and numerous vulnerabilities have been posted to security lists that describe exactly how certain database applications can be exploited. This article was written for the curious non-SQL experts who do not care to know the details, and as a review to those who do use SQL regularly.

45、What Is a SQL Server? A database application is a program that provides clients with access to data. There are many variations of this type of application, ranging from the expensive enterprise-level Microsoft SQL Server to the free and open source mySQL. 14 扬州大学计算机专业毕业设计(外文翻译) Regardless of the fla

46、vor, most database server applications have several things in common. First, database applications use the same general programming language known as SQL, or Structured Query Language. This language, also known as a fourth-level language due to its simplistic syntax, is at the core of how a client c

47、ommunicates its requests to the server. Using SQL in its simplest form, a programmer can select, add, update, and delete information in a database. However, SQL can also be used to create and design entire databases, perform various functions on the returned information, and even execute other progr

48、ams. To illustrate how SQL can be used, the following is an example of a simple standard SQL query and a more powerful SQL query: Simple: Select * from dbFurniture.tblChair This returns all information in the table tblChair from the database dbFurniture. 15 扬州大学计算机专业毕业设计(外文翻译) Complex: EXEC master.x

49、p_cmdshell dir c: This short SQL command returns to the client the list of files and folders under the c: directory of the SQL server. Note that this example uses an extended stored procedure that is exclusive to MS SQL Server. The second function that database server applications share is that they

50、 all require some form of authenticated connection between client and host. Although the SQL language is fairly easy to use, at least in its basic form, any client that wants to perform queries must first provide some form of credentials that will authorize the client; the client also must define th

51、e format of the request and response. This connection is defined by several attributes, depending on the relative location of the client and what operating systems are in use. We could spend a whole article discussing various technologies such as DSN connections, DSN-less 16 扬州大学计算机专业毕业设计(外文翻译) conn

52、ections, RDO, ADO, and more, but these subjects are outside the scope of this article. If you want to learn more about them, a little Googleing will provide you with more than enough information. However, the following is a list of the more common items included in a connection request. Database sou

53、rce Request type Database User ID Password Before any connection can be made, the client must define what type of database server it is connecting to. This is handled by a software component that provides the client with the instructions needed to create the request in the correct format. In additio

54、n to the type of database, the request type can be used to further define how the clients request will be handled by the server. Next comes the database name and finally the 17 扬州大学计算机专业毕业设计(外文翻译) authentication information. All the connection information is important, but by far the weakest link is

55、 the authentication informationor lack thereof. In a properly managed server, each database has its own users with specifically designated permissions that control what type of activity they can perform. For example, a user account would be set up as read only for applications that need to only acce

56、ss information. Another account should be used for inserts or updates, and maybe even a third account would be used for deletes. This type of account control ensures that any compromised account is limited in functionality. Unfortunately, many database programs are set up with null or easy passwords, which leads to successful hack attacks. 18 扬州大学计算机专业毕业设计(外文翻译) 译文 数据库管理系统介绍 数据库（database,有时拼作data base）又称为电子数据库，是专门组织起来的一组数据或信息，其目的是为了便于计算机快速查询及检索。数据库的结构是专门设计的，在各种数据处理操作命令的支持下，可以简化数据的存储，检索，修改和删除。数据库可以存储在磁盘，磁带，光盘或其他辅助存储设备上。 数据库由一个或一套文件组成，其中的信息可以分解为记录，每一记录又包含一个或多个字段（或称为域）。字段