外文資料翻譯-----數(shù)據(jù)庫管理系統(tǒng)的介紹-資料下載頁
2024-11-13 11:56本頁面
【導(dǎo)讀】的一組數(shù)據(jù)或信息，其目的是為了便于計(jì)算機(jī)快速查詢及檢索。一個(gè)或多個(gè)字段。字段是數(shù)據(jù)存取的基本單位。其中的一個(gè)字段通常表示與實(shí)體的某一屬性相關(guān)的信息。所有數(shù)據(jù)庫中都有復(fù)雜的數(shù)據(jù)關(guān)系及其鏈接。用程序員，管理員及其他需要信息的人員和各種操作系統(tǒng)程序）。DBMS可組織，處理和表示從數(shù)據(jù)庫中選出的數(shù)據(jù)元。該功能使決策者能搜索，們可以瀏覽數(shù)據(jù)庫直到獲得所需的信息。簡(jiǎn)言之，DBMS將“管理”存儲(chǔ)的數(shù)據(jù)項(xiàng)，并從公共數(shù)據(jù)庫中匯集所需的數(shù)據(jù)項(xiàng)以回答非程序員的詢問。在提高數(shù)據(jù)庫管理系統(tǒng)的價(jià)值和有效性方面正在展。人員需要最新的信息以做出有效的決策。，他們利用數(shù)據(jù)庫系統(tǒng)領(lǐng)先于競(jìng)爭(zhēng)對(duì)手。據(jù)庫管理方法，使用表作為數(shù)據(jù)結(jié)構(gòu),稱之為關(guān)系模型.的行和稱作字段的列組成。分布式數(shù)據(jù)庫的一個(gè)目的是訪問數(shù)據(jù)信息時(shí)不必考慮其他位置。器模型為分布式數(shù)據(jù)庫提供了框架結(jié)構(gòu)。器是一個(gè)運(yùn)行著的計(jì)算機(jī)軟件，存儲(chǔ)著那些通過網(wǎng)絡(luò)傳輸?shù)纳暾?qǐng)。
【正文】 e 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 today’s personal puters, departmental puters, and distributed processing require puters and their applications to municate with each other on a more equal or peertopeer basis. In a database, the client/server model provides the framework for distributing databases. One way to take advantage of many connected puters running database applications is to distribute the application into cooperating parts that are independent of one anther. A client is an end user or puter program that requests resources across a work. A server is a puter running software that fulfills those requests across a work . When the resources are data in a database ,the client/server model provides the framework for distributing database. A file serve is software that provides access to files across a work. A dedicated file server is a single puter dedicated to being a file server. This is useful ,for example ,if the files are large and require fast access .In such cases, a miniputer or mainframe would be used as a file server. A distributed file server spreads the files around on individual puters instead of placing them on one dedicated puter. Advantages of the latter server include the ability to store and retrieve files on other puters and the elimination of duplicate files on each puter. A major disadvantage , however, is that individual read/write requests are being moved across the work and problems can arise when updating files. Suppose a user requests a record from a file and changes it while another user 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 server is software that services requests to a database across a work. For example, suppose a user types in a query for data on his or her personal puter . If the application is designed with the client/server model in mind ,the query language part on the personal puter simple sends the query across the work 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. Sun’s Network Filing System(NFS),for example, is used in puteraided engineering applications to distribute data among the hard disks in a work of Sun workstation. Distributing databases is an evolutionary step because it is logical that data should exist at the location where they are being used . Departmental puters within a large corporation ,for example, should have data reside locally , 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 nondistributed database .
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