中英文翻译--数据库基础.doc

Database Fundamentals Introduction to DBMS A database management system (DBMS) is an important type of programming system, used today on the biggest and the smallest computers. As for other major forms of system software, such as compilers and operating systems, a well-understood set of principles for database management systems has developed over the years, and these concepts are useful both for understanding how to use these systems effectively and for designing and implementing DBMSs. DBMS is a collection of programs that enables you to store, modify, and extract information from a database. There are many different types of DBMSs, ranging from small systems that run on personal computers to huge systems that run on mainframes. There are two qualities that distinguish database management systems from other sorts of programming systems. 1) The ability to manage persistent data, and 2) The ability to access large amounts of data efficiently. Point 1) merely states that there is a database which exists permanently; the content of this database is the data that a DBMS accesses and manages. Point 2) distinguishes a DBMS from a file system, which also manages persistent data. A DBMSs capabilities are needed most when the amount of data is very large, because for small amounts of data, simple access techniques, such as linear scans of the data, are usually adequate. While we regard the above two properties of a DBMS as fundamental, there are a number of other capabilities that are almost universally found in commercial DBMSs. These are: (1) Support for at least one data model, or mathematical abstraction through which the user can view the data. (2) Support for certain high-level languages that allow the user to define the structure of data, access data, and manipulate data. (3) Transaction management, the capability to provide correct, concurrent