外文資料翻譯-----數(shù)據(jù)庫管理系統(tǒng)的介紹-展示頁
2024-11-25 11:56本頁面
【正文】 odel 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 . 。(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。 附件 2：外文原文 A introduction to Database Management System Raghu Ramakrishnan A database (sometimes spelled data base) is also called an electronic database , referring to any collection of data, or information, that is specially anized for rapid search and retrieval by a puter. Databases are structured to facilitate the storage, retrieval , modification, and deletion of data in conjunction with various dataprocessing operations .Databases can be stored on magic disk or tape, optical disk, or some other secondary storage device. A database consists of a file or a set of files. The information in these files may be broken down into records, each of which consi
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