You know that a data base 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. There's nothing new about data bases-early ones were chiseled in stone, penned on scrolls, and written on index cards. But now data bases are commonly recorded on magnetizable media, and computer programs are required to perform the necessary storage and retrieval operations.
You'll see in the following pages that complex data relationships and linkages may be found in all but the simplest data bases. The system software package that handles the difficult tasks associated with creating, accessing, and maintaining data base records is called a data basemanagement system (DBMS). The programs in a DBMS package establish an interface between the data base itself and the users of the data base. （These users may be applications programmers, managers and others with information needs, and various OS programs. ）
A DBMS can organize, process, and present selected data elements from the data base. This capability enables decision makers to search, probe, and query data base contents in order to extract answers to nonrecurring and unplanned questions that aren't available in regular reports. These questions might initially be vague and/or poorly defined, but people can"browse"through the data base until they have the needed information. In short, the DBMS will"manage"the stored data items and assemble the needed items from the common data base in response to the queries of those who aren't 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.
