數(shù)據(jù)庫管理系統(tǒng)中英文對(duì)照

1、1數(shù)據(jù)庫管理系統(tǒng)的介紹Raghu Ramakrishnan數(shù)據(jù)庫（database,有時(shí)拼作data base） 乂稱為電子數(shù)據(jù)庫，是專門組織 起來的一組數(shù)據(jù)或信息，其目的是為了便于計(jì)算機(jī)快速查詢及檢索。 數(shù)據(jù)庫的結(jié) 構(gòu)是專門設(shè)計(jì)的，在各種數(shù)據(jù)處理操作命令的支持下， 可以簡(jiǎn)化數(shù)據(jù)的存儲(chǔ)，檢 索，修改和刪除。數(shù)據(jù)庫可以存儲(chǔ)在磁盤，磁帶，光盤或其他輔助存儲(chǔ)設(shè)備上。數(shù)據(jù)庫由一個(gè)或一套文件組成，其中的信息可以分解為記錄，每一記錄乂包 含一個(gè)或多個(gè)字段（或稱為域）。字段是數(shù)據(jù)存取的基本單位。數(shù)據(jù)庫用于描述 實(shí)體，其中的一個(gè)字段通常表示與實(shí)體的某一屆性相關(guān)的信息。通過關(guān)鍵字以及 各種分類（排序）命令，用戶

2、可以對(duì)多條記錄的字段進(jìn)行查詢，重新整理，分組 或選擇，以實(shí)體對(duì)某一類數(shù)據(jù)的檢索，也可以生成報(bào)表。所有數(shù)據(jù)庫（最簡(jiǎn)單的除外）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)軟件包叫做數(shù)據(jù)庫管理系統(tǒng)（DBM& DBMSa件包中的程序在數(shù)據(jù)庫與其用戶間建立接口。（這些用戶可以是應(yīng)用程序員，管理員及其他需要信息的人員和各種操作系統(tǒng)程序）。DBMSM組織，處理和表示從數(shù)據(jù)庫中選出的數(shù)據(jù)元。該功能使決策者能搜 索，探查和查詢數(shù)據(jù)庫的內(nèi)容， 從而對(duì)在正規(guī)報(bào)告中沒有的， 不再出現(xiàn)的且無法 預(yù)料的問題做出回答。這些問題最初可能是模糊的并且（或者）是定義不恰當(dāng)?shù)模?但

3、是人們可以瀏覽數(shù)據(jù)庫直到獲得所需的信息。簡(jiǎn)言之，DBMS務(wù)“管理”存儲(chǔ)的數(shù)據(jù)項(xiàng)，并從公共數(shù)據(jù)庫中匯集所需的數(shù)據(jù)項(xiàng)以回答非程序員的詢問。DBM割3個(gè)主要部分組成：（1）存儲(chǔ)子系統(tǒng)，用來存儲(chǔ)和檢索文件中的數(shù) 據(jù)；（2）建模和操作子系統(tǒng)，提供組織數(shù)據(jù)以及添加，刪除，維護(hù)，更新數(shù)據(jù)的 方法；（3）用戶和DBM玄問的接口。在提高數(shù)據(jù)庫管理系統(tǒng)的價(jià)值和有效性方 面正在展現(xiàn)以下一些重要發(fā)展趨勢(shì)；1.管理人員需要最新的信息以做出有效的決策。2.客戶需要越來越復(fù)雜的信息服務(wù)以及更多的有關(guān)其訂單，發(fā)票和賬號(hào)的當(dāng) 前信息。3.用戶發(fā)現(xiàn)他們可以使用傳統(tǒng)的程序設(shè)計(jì)語言， 在很短的一段時(shí)間內(nèi)用數(shù)據(jù) 庫系統(tǒng)開發(fā)客戶應(yīng)用程序

4、。4.商業(yè)公司發(fā)現(xiàn)了信息的戰(zhàn)略價(jià)值，他們利用數(shù)據(jù)庫系統(tǒng)領(lǐng)先于競(jìng)爭(zhēng)對(duì)手。數(shù)據(jù)庫模型2數(shù)據(jù)庫模型描述了在數(shù)據(jù)庫中結(jié)構(gòu)化和操縱數(shù)據(jù)的方法， 模型的結(jié)構(gòu)部分規(guī) 定了數(shù)據(jù)如何被描述（例如樹，表等）：模型的操縱部分規(guī)定了數(shù)據(jù)添加，刪除， 顯示，維護(hù)，打印，查找，選擇，排序和更新等操作。分層模型第一個(gè)數(shù)據(jù)庫管理系統(tǒng)使用的是分層模型， 也就是說，將數(shù)據(jù)記錄排列成樹 形結(jié)構(gòu)。一些記錄時(shí)根目錄，在其他所有記錄都有獨(dú)立的父記錄。 樹形結(jié)構(gòu)的設(shè) 計(jì)反映了數(shù)據(jù)被使用的順序，也就是首先訪問處于樹根位置的記錄， 接下來是跟 下面的記錄，等等。分層模型的開發(fā)是因?yàn)榉謱雨P(guān)系在商業(yè)應(yīng)用中普遍存在， 眾所周知，一個(gè)組 織結(jié)構(gòu)圖表就

5、描述了一種分層關(guān)系：高層管理人員在最高層，中層管理人員在較 低的層次，負(fù)責(zé)具體事務(wù)的雇員在最底層。 值得注意的是，在一個(gè)嚴(yán)格的分層結(jié) 構(gòu)體系中，在每個(gè)管理層下可能有多個(gè)雇員或多個(gè)層次的雇員， 但每個(gè)雇員只有 一個(gè)管理者。分層結(jié)構(gòu)數(shù)據(jù)的典型特征是數(shù)據(jù)之間的一對(duì)多關(guān)系。在分層方法中，當(dāng)數(shù)據(jù)庫建立時(shí)，每一關(guān)系即被明確地定義。在分層數(shù)據(jù)庫 中的每一記錄只能包含一個(gè)關(guān)鍵字段， 任意兩個(gè)字段之間只能有一種關(guān)系。由于 數(shù)據(jù)并不總是遵循這種嚴(yán)格的分層關(guān)系，所以這樣可能會(huì)出現(xiàn)一些問題。關(guān)系模型在1970年，數(shù)據(jù)庫研究取得了重大突破。E.F.Codd提出了一種截然不同的 數(shù)據(jù)庫管理方法，使用表作為數(shù)據(jù)結(jié)構(gòu)，稱之為

6、關(guān)系模型.關(guān)系數(shù)據(jù)庫是使用最廣的數(shù)據(jù)結(jié)構(gòu)，數(shù)據(jù)被組織成關(guān)系表，每個(gè)表由稱作記 錄的行和稱作字段的列組成。每個(gè)記錄包含了專用項(xiàng)目的字段值。 例如，在一個(gè) 包含雇員信息的表中，一個(gè)記錄包含了像一個(gè)人姓名和地址這樣的字段的值。結(jié)構(gòu)化查詢語言（SQL是一種在關(guān)系型數(shù)據(jù)庫中用于處理數(shù)據(jù)的查詢語言。 它是非過程化語言或者說是描述性的，用戶只須指定一種類似于英語的描述，用 來確定操作，記錄或描述記錄組合。查詢優(yōu)化器將這種描述翻譯為過程執(zhí)行數(shù)據(jù) 庫操作。網(wǎng)狀模型網(wǎng)狀模型在數(shù)據(jù)之間通過鏈接表結(jié)構(gòu)創(chuàng)建關(guān)系，子記錄可以鏈接到多個(gè)父記 錄。這種將記錄和鏈接捆綁到一起的方法叫做指針，他是指向一個(gè)記錄存儲(chǔ)位置 的存儲(chǔ)地址

7、。使用網(wǎng)狀方法，一個(gè)子記錄可以鏈接到一個(gè)關(guān)鍵記錄，同時(shí)，它本 身也可以作為一個(gè)關(guān)鍵記錄。鏈接到其他一系列子記錄。在早期，網(wǎng)狀模型比其 他模型更有性能優(yōu)勢(shì)；但是在今天，這種優(yōu)勢(shì)的特點(diǎn)只有在自動(dòng)柜員機(jī)網(wǎng)絡(luò)， 航 空預(yù)定系統(tǒng)等大容量和高速處理過程中才是最重要的。3分層和網(wǎng)狀數(shù)據(jù)庫都是專用程序，如果開發(fā)一個(gè)新的應(yīng)用程序，那么在不同 的應(yīng)用程序中保持?jǐn)?shù)據(jù)庫的一致性是非常困難的。例如開發(fā)一個(gè)退休金程序，需 要訪問雇員數(shù)據(jù)，這一數(shù)據(jù)同時(shí)也被工資單程序訪問。 雖然數(shù)據(jù)是相同的，但是 也必須建立新的數(shù)據(jù)庫。對(duì)象模型最新的數(shù)據(jù)庫管理方法是使用對(duì)象模型，記錄由被稱作對(duì)象的實(shí)體來描述，可以在對(duì)象中存儲(chǔ)數(shù)據(jù)，同時(shí)提供方

8、法或程序執(zhí)行特定的任務(wù)。對(duì)象模型使用的查詢語言與開發(fā)數(shù)據(jù)庫程序所使用的面向?qū)ο蟮某绦蛟O(shè)計(jì) 語言是相同的，因?yàn)闆]有像SQLS樣簡(jiǎn)單統(tǒng)一的查詢語言，所以會(huì)產(chǎn)生一些問題。 對(duì)象模型相對(duì)較新，僅有少數(shù)幾個(gè)面向?qū)ο蟮臄?shù)據(jù)庫實(shí)例。它引起了人們的關(guān)注， 因?yàn)檫x擇面向?qū)ο蟪绦蛟O(shè)計(jì)語言的開發(fā)人員希望有一個(gè)基于在對(duì)象模型基礎(chǔ)上 的數(shù)據(jù)庫。分布式數(shù)據(jù)庫類似的， 分布式數(shù)據(jù)庫指的是數(shù)據(jù)庫的各個(gè)部分分別存儲(chǔ)在物理上相互分開 的計(jì)算機(jī)上。分布式數(shù)據(jù)庫的一個(gè)目的是訪問數(shù)據(jù)信息時(shí)不必考慮其他位置。注意，一旦用戶和數(shù)據(jù)分開，通信和網(wǎng)絡(luò)則開始扮演重要角色。分布式數(shù)據(jù)庫需要部分常駐于大型主機(jī)上的軟件， 這些軟件在大型機(jī)和個(gè)人 計(jì)算

9、機(jī)之間建立橋梁，并解決數(shù)據(jù)格式不兼容的問題。 在理想情況下，大型主機(jī) 上的數(shù)據(jù)庫看起來像是一個(gè)大的信息倉庫,而大部分處理則在個(gè)人計(jì)算機(jī)上完 成。分布式數(shù)據(jù)庫系統(tǒng)的一個(gè)缺點(diǎn)是它們常以主機(jī)中心模型為基礎(chǔ)，在這種模型中，大型主機(jī)看起來好像是雇主，而終端和個(gè)人計(jì)算機(jī)看起來好像是奴隸。但是 這種方法也有許多優(yōu)點(diǎn)：由于數(shù)據(jù)庫的集中控制，前面提到的數(shù)據(jù)完整性和安全 性的問題就迎刃而解了。當(dāng)今的個(gè)人計(jì)算機(jī)，部門級(jí)計(jì)算機(jī)和分布式處理都需要 計(jì)算機(jī)之間以及應(yīng)用程序之間在相等或?qū)Φ鹊幕A(chǔ)上相互通信，在數(shù)據(jù)庫中客戶機(jī)/服務(wù)器模型為分布式數(shù)據(jù)庫提供了框架結(jié)構(gòu)。利用相互連接的計(jì)算機(jī)上運(yùn)行的數(shù)據(jù)庫應(yīng)用程序的一種方法是將程序

10、分解 為相互獨(dú)立的部分?？蛻舳耸且粋€(gè)最終用戶或通過網(wǎng)絡(luò)申請(qǐng)資源的計(jì)算機(jī)程序，服務(wù)器是一個(gè)運(yùn)行著的計(jì)算機(jī)軟件， 存儲(chǔ)著那些通過網(wǎng)絡(luò)傳輸?shù)纳暾?qǐng)。當(dāng)申請(qǐng)的 資源是數(shù)據(jù)庫中的數(shù)據(jù)時(shí)，客戶機(jī)/服務(wù)器模型則為分布式數(shù)據(jù)庫提供了框架結(jié) 構(gòu)。文件服務(wù)器指的是一個(gè)通過網(wǎng)絡(luò)提供文件訪問的軟件，專門的文件服務(wù)器是 一臺(tái)被指定為文件服務(wù)器的計(jì)算機(jī)。 這是非常有用的，例如，如果文件比較大而 且需要快速訪問，在這種情況下，一臺(tái)微型計(jì)算機(jī)或大型主機(jī)將被用作文件服務(wù) 器。分布式文件服務(wù)器將文件分散到不同的計(jì)算機(jī)上，而不是將它們集中存放到 專門的文件服務(wù)器上。4后一種文件服務(wù)器的優(yōu)點(diǎn)包括在其他計(jì)算機(jī)上存儲(chǔ)和檢索文件的能力，并可

11、以在每一臺(tái)計(jì)算機(jī)上消除重復(fù)文件。然而，一個(gè)重要的缺點(diǎn)是每個(gè)讀寫請(qǐng)求需要 在網(wǎng)絡(luò)上傳播，在刷新文件時(shí)可能出現(xiàn)問題。假設(shè)一個(gè)用戶申請(qǐng)文件中的一個(gè)數(shù) 據(jù)并修改它，同時(shí)另外一個(gè)用戶也申請(qǐng)這個(gè)數(shù)據(jù)并修改它， 解決這種問題的方法 叫做數(shù)據(jù)鎖定，即第一個(gè)申請(qǐng)使其他申請(qǐng)?zhí)幱诘却隣顟B(tài)，直到完成第一個(gè)申請(qǐng)， 其他用戶可以讀取這個(gè)數(shù)據(jù)，但不能修改。數(shù)據(jù)庫服務(wù)器是一個(gè)通過網(wǎng)絡(luò)為數(shù)據(jù)庫申請(qǐng)?zhí)峁┓?wù)的軟件，例如，假設(shè)某個(gè)用戶在他的個(gè)人計(jì)算機(jī)上輸入了一個(gè)數(shù)據(jù)查詢命令，如果應(yīng)用程序按照客戶機(jī) /服務(wù)器模型設(shè)計(jì)，那么個(gè)人計(jì)算機(jī)上的查詢語言通過網(wǎng)絡(luò)傳送數(shù)據(jù)庫服務(wù)器上，當(dāng)發(fā)現(xiàn)數(shù)據(jù)時(shí)發(fā)出通知。在工程界也有許多分布式數(shù)據(jù)庫的例子， 如

12、SU修司的網(wǎng)絡(luò)文件系統(tǒng)（NFS被應(yīng)用到計(jì)算機(jī)輔助工程應(yīng)用程序中，將數(shù)據(jù)分散到由SUNC作站組成的網(wǎng)絡(luò)上 的不同硬盤之間。分布式數(shù)據(jù)庫是革命性的進(jìn)步，因?yàn)榘褦?shù)據(jù)存放在被使用位置上是很合乎常 理的。例如一個(gè)大公司不同部門之間的計(jì)算機(jī)，應(yīng)該將數(shù)據(jù)存儲(chǔ)在本地，然而， 當(dāng)被授權(quán)的管理人員需要整理部門數(shù)據(jù)時(shí)，數(shù)據(jù)應(yīng)該能夠被訪問。數(shù)據(jù)庫信息系 統(tǒng)軟件將保護(hù)數(shù)據(jù)庫的安全性和完整性， 對(duì)用戶而言，分布式數(shù)據(jù)庫和非分布式 數(shù)據(jù)庫看起來沒有什么差別。原文Database Management Systems( 3th Edition ),Wiley ,2004, 5-12A introduction to Data

13、base Management SystemRaghu RamakrishnanA database (sometimes spelled data base) is also called an electronic databasereferring to any collection of data, or information, that is specially organized forrapid search and retrieval by a computer. Databases are structured to facilitate thestorage, retri

14、eval , modification, and deletion of data in conjunction with variousdata-processing operations .Databases can be stored on magnetic disk or tape, opticaldisk, or some other secondary storage device.A database consists of a file or a set of files. The information in these filesmay be broken down int

15、o records, each of which consists of one or more fields. Fieldsare the basic units of data storage , and each field typically contains informationpertaining to one aspect or attribute of the entity described by the database . Using5keywords and various sorting commands, users can rapidly search , re

16、arrange, group,and select the fields in many records to retrieve or create reports on particularaggregate of data.Complex data relationships and linkages may be found in all but the simplestdatabases .The system software package that handles the difficult tasks associated withcreating ,accessing, an

17、d maintaining database records is called a database managementsystem(DBMS).The programs in a DBMS package establish an interface between thedatabaseitself and the users of the database.(These users may be applicationsprogrammers, managers and others with information needs, and various OS programs.)A

18、 DBMS can organize, process, and present selected data elements form the database.This capability enables decision makers to search, probe, and query database contentsin order to extract answers to nonrecurring and unplanned questions that arentavailable in regular reports. These questions might ini

19、tially be vague and/or poorlydefined ,but people can browse” through the database until they have the neededinformation. In short, the DBMS will manage the stored data items and assemble theneeded items from the common database in response to the queries of those who arentprogrammers.A database mana

20、gement system (DBMS) is composed of three major parts:(1)a storagesubsystem that stores and retrieves data in files;(2) a modeling and manipulationsubsystem that provides the means with which to organize the data and to add , delete,maintain, and update the data;(3)and an interface between the DBMS

21、and its users. Severalmajor trends are emerging that enhance the value and usefulness of database managementsystems;Managers: who require more up-to-data information to make effective decisionCustomers: who demand increasingly sophisticated information services and morecurrent information about the

22、status of their orders, invoices, and accounts. Users:who find that they can develop custom applications with database systems in afraction of the time it takes to use traditional programming languages.Organizations : that discover information has a strategic value; they utilizetheir database system

23、s to gain an edge over their competitors.6TheThe DatabaseDatabase ModelModelA data model describes a way to structure and manipulate the data in a database.The structural part of the model specifies how data should be represented(such as tree,tables, and so on ).The manipulative part of the model sp

24、ecifies the operation withwhich to add, delete, display, maintain, print, search, select, sort and update thedata. HierarchicalHierarchical ModelModelThe first database management systems used ahierarchical model-that is-theyarranged records into a tree structure. Some records are root records and a

25、ll othershave unique parent records. The structure of the tree is designed to reflect the orderin which the data will be used that is ,the record at the root of a tree will be accessedfirst, then records one level below the root ,and so on.The hierarchical model was developed because hierarchical re

26、lationships arecommonly found in business applications. As you have known, an organization char oftendescribes a hierarchical relationship: top managementis at the highest level, middlemanagement at lower levels, and operational employees at the lowest levels.Note that within a strict hierarchy, eac

27、h level of management may have many employeesor levels of employees beneath it, but each employee has only one manager. Hierarchicaldata are characterized by this one-to-many relationship among data.In the hierarchical approach, each relationship must be explicitly defined whenthe database is create

28、d. Each record in a hierarchical database can contain only onekey field and only one relationship is allowed between any two fields. This can createa problem because data do not always conform to such a strict hierarchy.RelationalRelational ModelModelA major breakthrough in database research occurre

29、d in 1970 when E. F. Codd proposeda fundamentally different approach to database management called relationalmodel ,which uses a table as its data structure.The relational databaseis the most widely used database structure. Data isorganized into related tables. Each table is made up of rows called a

30、nd columns calledfields. Each record contains fields of data about some specific item. For example, ina table containing information on employees, a record would contain fields of data suchas a persons last name ,first name ,and street address.7Structured query language(SQL)is a query language for m

31、anipulating data in arelational database .It is nonprocedural or declarative, in which the user need onlyspecify an English-like description that specifies the operation and the describedrecord or combination of records. A query optimizer translates the description intoa procedure to perform the dat

32、abase manipulation.NetworkNetwork ModelModelThe network model creates relationships among data through a linked-list structurein which subordinate records can be linked to more than one parent record. This approachcombines records with links, which are called pointers. The pointers are addressesthat

33、indicate the location of a record. With the network approach, a subordinate record canbe linked to a key record and at the same time itself be a key record linked to othersets of subordinate records. The network mode historically has had a performanceadvantage over other database models. Today , suc

34、h performance characteristics are onlyimportant in high-volume ,high-speed transaction processingsuch as automatic teller machine networks or airline reservation system.Both hierarchical and network databasesare application specific. If a newapplication isdeveloped,maintainingtheconsistencyofdatabas

35、esin differentapplications can be very difficult. For example, suppose a new pension application isdeveloped .The data are the same, but a new database must be created.ObjectObject ModelModelThe newest approach to database management uses an object model , in which recordsare represented by entities

36、 called objects that can both store data and provide methodsor procedures to perform specific tasks.The query language used for the object model is the same object-orientedprogramming language used to develop the database application .This can create problemsbecausethere is no simple , uniform query

37、 language such as SQL . The object model isrelatively new, and only a few examples of object-oriented database exist. It hasattracted attention becausedevelopers who choose an object-oriented programminglanguage want a database based on an object-oriented model.DistributedDistributed DatabaseDatabas

38、eSimilarly , a distributed database is one in which different parts of the databasereside on physically separatedcomputers . One goal of distributed databasesis the access8of information without regard to where the data might be stored. Keeping in mind thatonce the users and their data are separated

39、, the communication and networking conceptscome into play .Distributed databases require software that resides partially in the largercomputer. This software bridges the gap between personal and large computers andresolves the problems of incompatible data formats. Ideally, it would make the mainfra

40、medatabasesappear to be large libraries of information, with most of the processingaccomplished on the personal computer.A drawback to some distributed systems is that they are often based on what iscalled a mainframe-entire model , in which the larger host computer is seen as the masterand the term

41、inal or personal computer is seen as a slave. There are some advantagesto this approach . With databases under centralized control , many ofthe problems ofdata integrity that we mentioned earlier are solved . But todays personal computers,departmental computers, and distributed processing require co

42、mputers and theirapplications to communicate with each other on a more equal or peer-to-peer basis. Ina database, the client/server model provides the framework for distributing databases.Onewaytotakeadvantageofmanyconnectedcomputersrunningdatabaseapplications is to distribute the application into c

43、ooperating parts that areindependent of one anther. A client is an end user or computer program that requestsresources across a network. A server is a computer running software that fulfills thoserequests across a network . When the resources are data in a database ,the client/servermodel provides t

44、he framework for distributing database.A file serve is software that provides access to files across a network. A dedicatedfile server is a single computer dedicated to being a file server. This is useful ,forexample ,if the files are large and require fast access .In such cases, a minicomputeror ma

45、inframe would be used as a file server. A distributed file server spreads the filesaround on individual computers instead of placing them on one dedicated computer.Advantages of the latter server include the ability to store and retrieve fileson other computers and the elimination of duplicate files on each computer. A majordisadvantage , however, is that individual read/write requests are being moved acrossthe network and problems can arise when updating files. Suppose a use