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(kù)管理系統(tǒng)(DBMS)
眾所周知，數(shù)據(jù)庫(kù)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(lái)，以滿足單位和個(gè)人的多種處理和檢索的需要。數(shù)據(jù)庫(kù)本身不是什么新鮮事——早期的數(shù)據(jù)庫(kù)鑿在石頭上，記在名冊(cè)上，以及寫入索引卡中。而現(xiàn)在，數(shù)據(jù)庫(kù)普遍記錄在可磁化的介質(zhì)上，并且需要用計(jì)算機(jī)程序來(lái)執(zhí)行必需的存儲(chǔ)和檢索操作。
在后文中你將看到除了最簡(jiǎn)單的以外，所有數(shù)據(jù)庫(kù)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(wèn)以及維護(hù)數(shù)據(jù)庫(kù)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(kù)管理系統(tǒng)(DBMS)。DBMS軟件包中的程序在數(shù)據(jù)庫(kù)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(kù)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(kù)的內(nèi)容，從而對(duì)在正式報(bào)告中沒(méi)有的、不再出現(xiàn)的且無(wú)計(jì)劃的問(wèn)題作出回答。這些問(wèn)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(kù)直到獲得問(wèn)題的答案。簡(jiǎn)言之，DBMS將“管理”存儲(chǔ)的數(shù)據(jù)項(xiàng)，并從公共數(shù)據(jù)庫(kù)中匯集所需的數(shù)據(jù)項(xiàng)以回答那些非程序員的詢問(wèn)。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(shí)間允許時(shí)，將編寫一個(gè)或多個(gè)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)