数据库系统------（外文翻译）.doc

DATABASE SYSYTEMS 12-1 DATA BASE MANAGEMENT SYSTEMS You know that a database is a collection of logically related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals. Theres nothing new about data bases-early ones were chiseled in stone, penned on scrolls, and written on index cards. But now databases are commonly recorded on magnetizeable media, and computer programs are required to perform the necessary storage and retrieval operations. Youll see in the following pages that complex data relationships and linkages may be found in all but the simplest databases. The system software package that handles the difficult tasks associated with creating, accessing, and maintaining data base records is called a data base management system (DBMS). The programs in a DBMS package establish an interface between the database itself and the users of the database. (These users may be applications programmers, managers and others with information needs, and various OS program.) A DBMS can organize, process, and present selected data elements from the database. This capability enables decision makers to search, probe, and query data base contents in order to extract answers to nonrecurring and unplanned questions that arent available in regular reports. These questions might initially be vague and/or poorly defined, but people can browse through the database until they have the needed information. In short, the DBMS will manage the stored data items and assemble the needed items from the common database in response to the queries of those who arent programmers. In a file -oriented system, users needing special information may communicate their needs to a programmer, who, when time permits, will write one or more programs to extract the data and prepare the information. The availability of a DBMS, however, offers users a much faster alternative communications path 12-2 DBMS STRUCTURING TECHNIQUES