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2025-02-06 04:21本頁面
【正文】 xist. It has attracted attention because developers who choose an objectorientedprogramming language want a database based on an objectoriented Database Similarly a distributed database is one in which different parts of the databasereside on physically separated puters . One goal of distributed databases is theaccess of information without regard to where the data might be stored. Keeping inmind that once the users and their data are separated the munication andworking concepts e into play . Distributed databases require software that resides partially in the largerputer. This software bridges the gap between personal and large puters andresolves the problems of inpatible data formats. Ideally it would make themainframe databases appear to be large libraries of information with most of theprocessing acplished on the personal puter. A drawback to some distributed systems is that they are often based on what iscalled a mainframeentire model in which the larger host puter is seen as themaster and the terminal or personal puter is seen as a slave. There are someadvantages to this approach . With databases under centralized control many of theproblems of data integrity that we mentioned earlier are solved . But today’s personalputers departmental puters and distributed processing require puters andtheir applications to municate with each other on a more equal or peertopeerbasis. In a database the client/server model provides the framework for distributingdatabases. One way to take advantage of many connected puters running databaseapplications is to distribute the application into cooperating parts that are independentof one anther. A client is an end user or puter program that requests resourcesacross a work. A server is a puter running software that fulfills those requestsacross a work . When the resources are data in a database the client/server modelprovides the framework for distributing database. A file serve is software that provides access to files across a work. Adedicated file server is a single puter dedicated to being a file server. This isuseful for example if the files are large and require fast access .In such cases aminiputer or mainframe would be used as a file server. A distributed file serverspreads the files around on individual puters instead of placing them on onededicated puter. Advantages of the latter server include the ability to store and retrieve files onother puters and the elimination of duplicate files on each puter. A majordisadvantage however is that individual read/write requests are being movedacross the work and problems can arise when updating files. Suppose a userrequests a record from a file and changes it
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