《计算机英语》第四单元.pptx

主要内容 正文 生词 A database-management system (DBMS) consists of a collection of interrelated data and a set of programs to access those data. The collection of data, usually referred to as the database, contains information about one particular enterprise. The primary goal of a DBMS is to provide an environment that is both convenient and efficient to use in retrieving and storing database information. 数据库管理系统（DBMS）由一个相互关联的数据的集合和一组可以访问这些数据的程序组成。这个数据集合，通常被称作包含一个特定企业的信息的数据库。DBMS的主要目的是提供一个便利而有效的环境，用来找回和存取数据库信息。 正文 Database systems are designed to manage large bodies of information. The management of data involves both the definition of structures for the storage of information and the provision of mechanisms for the manipulation of information. In addition, the database system must provide for the safety of the information stored, despite system crashes or attempts at unauthorized access. If data are to be shared among several users, the system must avoid possible anomalous results. The importance of information in most organizations， which determines the value of the database—has led to the development of a large body of concepts and techniques for the efficient management of data. 数据库系统原计划是用于管理大的信息体。数据的管理包括信息存储结构的定义，信息处理机制的规定。另外，数据库系统必须确保数据存储的安全性，即使是遇到系统受到撞击或未经允许的访问。如果数据在不同的用户中共享，这个系统必须避免一些可能存在的异常结果的出现。在大多数已确定数据库作用的组织中，信息的重要性表现为：它导致了与数据库的有效管理相关的一大批概念和技术的发展。 正文 The storage structure and access methods used by the database system are specified by a set of definitions in a special of DDL called a data storage and definition language? The result of compilation of these definitions is a set of instructions to specify the implementation details of the database schemas--details are usually hidden from the users. A database schema is also specified by DDL. Tile result of compilation of DDL statements is a set of tables that is stored in a special file called data dictionary, or data directory. A data dictionary is a file that contains metadata--that is, data about data. This file