关于分布式数据库系统的计算机英语

计算机英语 Distributed Database System A decentralized system-known in the database world as a distributed system can be highly responsive to differences in data gathering, storage, and access. It can adjust to differences in user psychol-ogy-between, say, a multinational corporation's employees in individualistic Greece and in disciplined Japan. It can also adapt to the management styles of strong managers in different locations. An organization that prefers homogeneity and top-down control will naturally choose a centralized database system. It may also prefer the hierarchical data model. By contrast, an organization that prefers local improvisation and free wheeling may well choose distributed database system. It may also choose the network data model ， which is well suited to searching and updating data in a distributed system. Communication between distributed commutinies of computer is required for many reasons.At a national level, for example, computers located in different parts of the country use public communication services to exchange electronic messages(mail) and to transfer files of information from one computer to another: Similarly, at a local level within, say, a single building or establishment, distributed communities of computer-based workstations use local communication networks to access expensive shared resources-for example, printers, copiers, disks and tapes, etc.-that are also managed by computers.Clearly, as the range of computer-based products and associated public and local commedication networks procreate, computer-to-computer communication will expand rapidly and ultimately dominate the field of distributed system. Historically, computers were so expensive that most large organizations did all their data processing on a single, centralized machine. While very efficient for such tasks as payroll and generating accounting reports, the centralized approach was very useful to those who needed a quick response to a unique, local problem. With today's inexpensive micros and minis, there is no reason why a branch office, the engineer-in department, or any other group needing computer support cannot have its own computer. By linking these remote machines to a centralized computer via communication lines, local activity can be monitored and coordinated. This approach is called distributed data processing. 分散式系统在数据库领域中称为分布式系统，这种系统能处理不同的数 据采集、存储和访问方一式。它可以根据用户的心理，例如可针对个性强的 希腊雇员和守纪律的日本雇员之间的差异作出调整，它也可适应不同地方的 各种管理人员的不同管理风格。 倾向于均质的、从上向下管理的组织机构自然要选择集中式数据库系统 ， 这种组织也乐于使用层次型数据模型。 相反，倾向于临时配置和对数据库循环访问的组织机构必然要选择分布 式数据库系统，这种组织也乐于选择网络型数据模型，因为这种模型根适合 于分布式系统数据查找和修改。 分布式计算机系统间需要进行通信有许多原因，例如在一个国家内，处 于各地的计算机使用公共通信设施交换电子信息(邮件)，从一个计算机向另 一个计算机传送文件。同样，在一个局部区域内。例如在一个大楼或机关内 ， 分布式的计算机工作站间 使用局部通信网络访问昂贵的共享资源，例如打印 机、复印机、 磁盘和磁带等，这些设备也由计算机管理。很明显，随着基于 计算机的产品和相应的公共及局部通信网络的激增，计算机一计算机通信也 将得到迅速的发展，最终将在分布式系统中占统治地位。 从历史上看，计算机是如此昂贵，这使得许多的大型组织机 构在作他们 的数据处理时都得用一台计算机一一中央机。这种集中处理的方法，对一些 如象工资 和财务报表等任务来说是非常有效的，然而对另一些任务，如象需 要对单一的、局部的问题作出快速相应的任务，就不是那么有效了。 由于现在微机和小型机都很便宜，因此在科室、工程部门， 或者任问需 要计算机支持工作的团体部可以拥有自己的计算机。用通讯线路线路把这些 远程机器与中央计算机相连接，局部的话动就可以被监视和协调。这种方式 称之为分布式数据处理。