外文資料翻譯-----數(shù)據(jù)庫管理系統(tǒng)的介紹-文庫吧資料
2024-11-21 11:56本頁面
【正文】 me itself be a key record linked to other sets of subordinate records. The work mode historically has had a performance advantage over other database models. Today , such performance characteristics are only important in highvolume ,highspeed transaction processing such as automatic teller machine works or airline reservation system. Both hierarchical and work databases are application specific. If a new application is developed ,maintaining the consistency of databases in different applications can be very difficult. For example, suppose 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 procedures to perform specific tasks. The query language used for the object model is the same objectoriented 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 a few examples of objectoriented database exist. It has attracted attention because developers who choose an objectoriented programming language want a database based on an objectoriented model. Distributed Database Similarly , a distributed database is one in which different parts of the database reside on physically separated puters . 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 munication and working concepts e into play . Distributed databases require software that resides partially in the larger puter. This software bridges the gap between personal and large puters and resolves the problems of inpatible data formats. Ideally, it would make the mainframe databases appear to be large libraries of information, with most of the processing acplished on the personal puter. A drawback to some distributed systems is that they are often based on what is called a mainframeentire model , in which the larger host puter is seen as the master and the terminal or personal puter 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 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 m
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