英语翻译Layers of Data AbstractionDatabases are unique in their

英语翻译
Layers of Data Abstraction
Databases are unique in their ability to present multiple users with their own distinct views of the data while storing the underlying data only once.These are collectively called user views.A user in this context is any person or application that signs on to the database for the purpose of storing and/or retrieving data.An application is a set of computer programs designed to solve a particular business problem,such as an order-entry system,a payroll-processing system,or an accounting system.
When an electronic spreadsheet application such as Microsoft Excel is used,all users must share a common view of the data,and that view must match the way the data is physically stored in the underlying data file.If a user hides some columns in a spreadsheet,reorders the rows,and saves the spreadsheet,the next user who opens the spreadsheet will view the data in the manner in which the first user saved it.An alternative,of course,is for each user to save his or her own copy in separate physical files,but then as one user applies updates,the other users' data becomes out of date.Database systems present each user a view of the same data,but the views can be tailored to the needs of the individual users,even though they all come from one commonly stored copy of the data.Because views store no actual data,they automatically reflect any data changes made to the underlying database objects.This is all possible through layers of abstraction,which is shown in Figure 1一1.
The architecture shown in Figure 1一1 was first developed by ANSI/SPARC (American National Standards Institute/Standards Planning and Requirements Committee) in the 1970s and quickly became a foundation for much of the database research and development efforts that followed.Most modern DBMSs follow this architecture,which is composed of three primary layers:the physical layer,the logical layer,and the external layer.The original architecture included a conceptual layer,which has been omitted here because none of the modern database vendors implement it.

数据抽象层
数据库是独一无二的能力提出自己的数据截然不同的意见多个用户,而底层的数据存储一次.这些统称用户的意见.这方面的一个用户是任何人或应用程序上标志为存储和/或数据库检索数据的目的.
应用程序是一个专为解决特定业务问题,计算机程序设置,如订单输入系统,工资单处理系统或会计制度.
当一个电子表格应用程序,如Microsoft Excel中使用,所有用户必须共享数据的共同的看法,并认为必须符合实际的数据是在基础数据文件的存储方式.如果用户在电子表格中隐藏某些列,行重新排序,并保存电子表格,
谁是下一个用户打开该电子表格将查看方式的第一个用户保存该数据.当然一个替代办法,为每个用户保存他或她在单独的物理文件的副本,但随后的一个用户适用的更新,其他用户的数据变成了现在的date.Database系统的每个用户都有一个相同的观点数据,但可以根据意见
对个人用户的需求,尽管他们都来自通常存储的数据的副本之一.由于意见不实际的数据存储,他们的任何数据自动反映所做的更改底层数据库对象.这是所有可能通过抽象层,这在如图1一1.
图1一1所示的体系结构最早是由ANSI / SPARC的（美国国家标准学会/标准规划和需求委员会）在20世纪70年代,并迅速成为了该数据库的研究和开发之后努力的主要基础.大多数现代的DBMS遵循这种体系结构,
这是由三个主要层次：物理层,逻辑层和外层.原来的架构,包括一个概念层,这是在这里被省略,因为现代数据库供应商没有执行.