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 retrieva l 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 databases are commonly recorded on magnetizeable media, and computer programs are required to perform the necessary storage and retrieva l operations.
You'll 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 aren't 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 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



12-1 數(shù)據(jù)庫管理系統(tǒng)(DBMS)
眾所周知，數(shù)據(jù)庫是邏輯上相關(guān)的數(shù)據(jù)元的集合。這些數(shù)據(jù)元可以按不同的結(jié)構(gòu)組織起來，以滿足單位和個人的多種處理和檢索的需要。數(shù)據(jù)庫本身不是什么新鮮事——早期的數(shù)據(jù)庫鑿在石頭上，記在名冊上，以及寫入索引卡中。而現(xiàn)在，數(shù)據(jù)庫普遍記錄在可磁化的介質(zhì)上，并且需要用計算機(jī)程序來執(zhí)行必需的存儲和檢索操作。
在后文中你將看到除了最簡單的以外，所有數(shù)據(jù)庫中都有復(fù)雜的數(shù)據(jù)關(guān)系及其鏈接。處理與創(chuàng)建、訪問以及維護(hù)數(shù)據(jù)庫記錄有關(guān)的復(fù)雜任務(wù)的系統(tǒng)軟件包叫作數(shù)據(jù)庫管理系統(tǒng)(DBMS)。DBMS軟件包中的程序在數(shù)據(jù)庫及其用戶間建立了接口(這些用戶可以是應(yīng)用程序員、管理員以及其他需要信息和各種操作系統(tǒng)的人員)。
DBMS可組織、處理和顯示從數(shù)據(jù)庫中選擇的數(shù)據(jù)元。該功能使決策者可以搜索、試探和查詢數(shù)據(jù)庫的內(nèi)容，從而對在正式報告中沒有的、不再出現(xiàn)的且無計劃的問題作出回答。這些問題最初可能是模糊的并且/或者是定義不清的，但是人們可以瀏覽數(shù)據(jù)庫直到獲得問題的答案。簡言之，DBMS將“管理”存儲的數(shù)據(jù)項，并從公共數(shù)據(jù)庫中匯集所需的數(shù)據(jù)項以回答那些非程序員的詢問。在面向文件的系統(tǒng)中，需要特定信息的用戶可以將他們的要求傳送給程序員。該程序員在時間允許時，將編寫一個或多個程序以提取數(shù)據(jù)和準(zhǔn)備信息。但是，使用DBMS可為用戶提供一種更快的、用戶可選擇的通信方式 (rutu)