1、客戶信息管理系統(tǒng)文獻(xiàn)綜述及 外文文獻(xiàn)翻譯華中科技大學(xué)文華學(xué)院畢業(yè)設(shè)計(jì)（論文）外文文獻(xiàn)翻譯（本科學(xué)生用）題目：客戶信息管理系統(tǒng)_學(xué)生 姓名：路雅寧 學(xué)號(hào):090102031117學(xué)部（系）：專業(yè)年級(jí)：09電子信息工程指導(dǎo)教師： 容太平職稱或?qū)W位:教授20 13 年 3 月 8 H外文文獻(xiàn)翻譯（譯成中文IOOO字左右）：【主要閱讀文獻(xiàn)不少于5篇，譯文后附注文獻(xiàn)信息,包括：作者.書名（或論文題目）.出版社（或刊物名稱）、出版時(shí)間（或刊號(hào)）.頁(yè)碼。提供所譯外文資料附件（印刷類含封面、封底.目錄.翻譯部分的復(fù)印件等，網(wǎng)站類的請(qǐng)附網(wǎng)址及原文】譯文數(shù)據(jù)庫(kù)管理系統(tǒng)介紹，數(shù)據(jù)庫(kù) database,時(shí)拼作data

2、 base,又稱為 電子數(shù)據(jù)庫(kù)，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)快速査 詢及檢索。數(shù)據(jù)庫(kù)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(kù)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(kù)由一個(gè)或一套文件組成其中的信息可以分解為記錄毎一記錄 又包含一個(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(kù)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JB性相關(guān)的信息。通過關(guān)鍵字以及各種分 類、排序、命令。用戶可以對(duì)多條記錄的字段進(jìn)行査詢，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(kù)，中

3、都有復(fù)雜的數(shù)據(jù)關(guān)系及 其璉接。處理與創(chuàng)建，訪問以及維護(hù)數(shù)據(jù)庫(kù)記錄有關(guān)的復(fù)雜任務(wù)的系統(tǒng)軟件包叫做數(shù) 據(jù)庫(kù)管理系統(tǒng)DBMSO DBMS軟件包中的程序在數(shù)據(jù)庫(kù)與其用戶間建立接口。這些 用戶可以是應(yīng)用程序員，管理員及其他滯要信息的人員和各種操作系統(tǒng)程序。DBMS 可組織處理和表示從數(shù)據(jù)庫(kù)中選出的數(shù)據(jù)元。該功能使決策者能搜索，探査和査詢數(shù) 據(jù)庫(kù)的內(nèi)容，從而對(duì)在正規(guī)報(bào)吿中沒有的，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橫糊的并且、或者是定義不恰當(dāng)?shù)模侨藗兛梢詾g覽數(shù)據(jù)庫(kù)BL 到獲得所需的信息。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)以回答非程序員的詢問。D

4、BMS由3個(gè)主要部分組成、1存儲(chǔ)子系統(tǒng): 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、 維扒 更新數(shù)據(jù)的方法，3用戶和DBMS之間的接口。在提高數(shù)據(jù)庫(kù)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)展趙勢(shì)，1 管理人員H要最新的信息以做 出有效的決策。2客戶IB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(yǔ)言在很短的一段時(shí) 間內(nèi)用數(shù)據(jù)庫(kù)系統(tǒng)開發(fā)客戶應(yīng)用程序。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(kù)系統(tǒng)領(lǐng)先于競(jìng)爭(zhēng)對(duì)手。數(shù)據(jù)庫(kù)模型數(shù)據(jù)庫(kù)模型描述了在數(shù)據(jù)庫(kù)中結(jié)構(gòu)化和 操縱數(shù)據(jù)的方法，橫型的結(jié)構(gòu)部分規(guī)定了

5、數(shù)據(jù)如何被描述，例如樹、表等，橫型的 操縱部分規(guī)定了數(shù)據(jù)添加、刪除、並示、維護(hù)、打印、査找、選擇、排厚和更新尊操 作。分民橫型：第一個(gè)數(shù)據(jù)庫(kù)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)被使用的順厚，也就是首先訪問處于樹根位!的記錄，接下來是跟下面的記錄 尊尊。分層橫型的開發(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I 一個(gè) 組織結(jié)構(gòu)圖表就描述了 一種分尿關(guān)系，高展管理人員在最高展，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SL值得注Jt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

6、能有多個(gè)匪員或多個(gè)展次的展員,但每個(gè)莊員只有一個(gè)管理者。 分辰結(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(kù)建立 時(shí)，每一關(guān)系即被明確地定義。在分展數(shù)據(jù)庫(kù)中的每一記錄只能包含一個(gè)關(guān)鍵字段， 任議兩個(gè)字段之間只能有一種關(guān)系。由于數(shù)據(jù)并不總是連循這種嚴(yán)格的分展關(guān)系，所 以這樣可能會(huì)出現(xiàn)一些問題。關(guān)系橫型在1970年，數(shù)據(jù)庫(kù)研究取得了更大突破。 E.F.Codd提出了一種戡然不同的數(shù)據(jù)庫(kù)管理方法，使用表作為數(shù)據(jù)結(jié)構(gòu),稱之為關(guān)系 橫型.關(guān)系數(shù)據(jù)庫(kù)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。毎個(gè)記錄包含了專用項(xiàng)目的字段值。例如，在一個(gè)包含展員 信

7、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)化査詢語(yǔ) SQL,是一種在關(guān)系型數(shù)據(jù)庫(kù)中用于處理數(shù)據(jù)的査詢語(yǔ)言。它是非過程化語(yǔ)言 或者說是描述性的，用戶只須指定一種類似于英語(yǔ)的描述，用來確定操作，記錄或描 述記錄組合。査詢優(yōu)化器將這種描述IB譯為過程執(zhí)行數(shù)據(jù)庫(kù)操作。網(wǎng)狀模型網(wǎng)狀模 型在數(shù)據(jù)之間通過璉接表結(jié)構(gòu)創(chuàng)建關(guān)系，子記錄可以粧接到多個(gè)父記錄。這種將記錄 和惟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at的存儲(chǔ)地址。使用網(wǎng) 狀方法，一個(gè)子記錄可以璉接到一個(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。儺接到其他一系列子記錄。在早期，網(wǎng)狀犠型比其他橫型更有性能優(yōu)勢(shì)，但是在

8、 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。分展和網(wǎng)狀數(shù)據(jù)庫(kù)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(kù)的一致性是非常困難的。例如開發(fā)一個(gè)退休 金程序，需要訪問匿員數(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(kù)。對(duì)氛橫型最新的數(shù)據(jù)庫(kù)管理方法是使用對(duì)象模型，記 錄由被稱作對(duì)氛的實(shí)體來描述，可以在對(duì)獄中存儲(chǔ)數(shù)據(jù)，同時(shí)提供方法或程序執(zhí)行特 定的任務(wù)。對(duì)氛橫型使用的査詢語(yǔ)言與開發(fā)數(shù)據(jù)庫(kù)程序所使用的面向?qū)ο蟮某绦蛟O(shè) 計(jì)語(yǔ)言是相同的，因?yàn)闆]有像SQL這樣簡(jiǎn)單統(tǒng)一的査詢語(yǔ)言，所以會(huì)產(chǎn)生一些問

9、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(kù)實(shí)例。它引起了人們的關(guān)注 因 為選擇面向?qū)ο蟪毯裨O(shè)計(jì)語(yǔ)言的開發(fā)人員希望有一個(gè)基于在對(duì)氛橫型基礎(chǔ)上的數(shù)據(jù) 庫(kù)。分布式數(shù)據(jù)庫(kù)類似的分布式數(shù)據(jù)庫(kù)指的是數(shù)據(jù)庫(kù)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(kù)的一個(gè)目的是訪問數(shù)據(jù)信息時(shí)不必考慮其他位 EO注直,一且用戶和數(shù)據(jù)分開 通信和網(wǎng)絡(luò)則開始扮湊更要角色。分布式數(shù)據(jù)庫(kù) 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(kù)看起來像是一個(gè) 大的信息倉(cāng)庫(kù)，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(kù)系統(tǒng)的一個(gè)

10、缺 點(diǎn)是它們常以主機(jī)中心摸型為基礎(chǔ)，在這種模型中，大型主機(jī)看起來好像是履主，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(kù)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?礎(chǔ)上相互通信，在數(shù)據(jù)庫(kù)中客戶機(jī)/服務(wù)器筷型為分布式數(shù)據(jù)庫(kù)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(kù)應(yīng)用程序的一種方法是將程序分解為相互獨(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) 行満的計(jì)算機(jī)軟件，存儲(chǔ)著那些通過網(wǎng)絡(luò)伎輸?shù)纳暾?qǐng)。當(dāng)申請(qǐng)的資源是數(shù)據(jù)庫(kù)

11、中的數(shù) 據(jù)時(shí)，客戶機(jī)/服務(wù)器橫型則為分布式數(shù)據(jù)庫(kù)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JB要快速訪問，在這種悄況下， 一臺(tái)微型計(jì)算機(jī)或大型主機(jī)將披用作文件服務(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。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)求播要在網(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

12、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)使其他申諸 處于等待狀態(tài)，St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(kù)服務(wù)器是一個(gè)通過網(wǎng)絡(luò)為數(shù)據(jù)庫(kù)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)査詢命令I(lǐng)如果應(yīng)用程厚按照客戶機(jī)/服務(wù)器橫型設(shè) 計(jì)，那么這個(gè)人計(jì)奠機(jī)上的査詢語(yǔ)言通過網(wǎng)絡(luò)傳送數(shù)據(jù)庫(kù)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(kù)的例子，如SUN公司的網(wǎng)絡(luò)文件系統(tǒng), NFS I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SUN工作站組成的網(wǎng) 絡(luò)上的不同碩盤之間。分布式數(shù)據(jù)庫(kù)是革命性的進(jìn)步，因

13、為把數(shù)據(jù)存放在被使用位 Il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)的管理人員補(bǔ)要88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(kù) 信息系統(tǒng)軟件將保護(hù)數(shù)據(jù)庫(kù)的安全性和完整性，對(duì)用戶而言，分布式數(shù)據(jù)庫(kù)和非分布 式數(shù)據(jù)庫(kù)看超來沒有什么差別。在這個(gè)信息時(shí)代，數(shù)據(jù)管理服務(wù)器已經(jīng)成為公司的 核心。這一個(gè)軟件的橫塊控制整個(gè)組織的順利運(yùn)行就如同人身體動(dòng)脈使得鮮血在身體 中流通順暢。因?yàn)檫@個(gè)所以就要把好身份申請(qǐng)這一關(guān)，數(shù)據(jù)管理服務(wù)器也是黑客最為 關(guān)心的目標(biāo)之一。如果一且自己的身份驗(yàn)證被黑客攻克,他將能引起公司的”心臟” 受致命的破壞。雖然大多數(shù)的使用者現(xiàn)在知道黑

14、客，但是他們?nèi)匀徊涣私馑麄兊臄?shù) 據(jù)庫(kù)伺候器是多么的易受影響黑客的攻擊。因此，這篇文章介紹是如何攻擊數(shù)據(jù)庫(kù)伺 候器（比如SQL伺候器）和講述你在受攻擊時(shí)該如何保護(hù)你自己的數(shù)據(jù)。 我們應(yīng) 該注意信息不斷更新。許多技術(shù)上的空白導(dǎo)致了 SQL在運(yùn)行時(shí)很多細(xì)節(jié)披攻擊的 事，而且很多的易受攻擊的地方披寄到完全地描述數(shù)據(jù)庫(kù)申請(qǐng)能是多么的某開發(fā)的安 全目錄。這個(gè)文章對(duì)那些好奇的非SQL專家是書面的不關(guān)心知道細(xì)節(jié)，而且如檢 討到那些做的人有規(guī)則地使用SQLO 一個(gè)SQL伺候器是做什么的，一個(gè)數(shù)據(jù)庫(kù) 身份驗(yàn)證是一個(gè)提供給有權(quán)限客戶訪問數(shù)據(jù)通道。申請(qǐng)的類型有許多變化,從大企業(yè) 的微軟SQL伺候器到自由的和開放來源m

15、ySQL排列。不管是什么，大多數(shù)的數(shù) 據(jù)庫(kù)伺候器申請(qǐng)都有共同的一些功能。首先數(shù)據(jù)庫(kù)申It使用都使用相同的SQL的 語(yǔ)言，或結(jié)構(gòu)査詢語(yǔ)言。這些語(yǔ)言，也厲于第四代語(yǔ)言,由于它單純化的語(yǔ)法，是在 一位客戶如何向伺候器傳達(dá)它的請(qǐng)求核心。使用它最簡(jiǎn)單的形式語(yǔ)言SQL I 一個(gè)程 序師能選擇,増加、更新、而且在一個(gè)數(shù)據(jù)庫(kù)中能劃分各種數(shù)據(jù)。然而，SQL也能用 來產(chǎn)生并且設(shè)計(jì)整個(gè)的數(shù)據(jù)庫(kù)，運(yùn)行被送回的數(shù)據(jù)上的各種不同的功能,甚至運(yùn)行其 他的程序。為了要舉例說明SQL如何使用,下列各項(xiàng)是簡(jiǎn)單標(biāo)準(zhǔn)SQL的一個(gè)例子 疑問和一個(gè)比較復(fù)雜的SQL疑問，簡(jiǎn)單的”挑選出來的，從dbFumiture.tblChairH 這在

16、來自數(shù)據(jù)庫(kù)dbFumiture的數(shù)據(jù)庫(kù)tblChair中返還的所有數(shù)據(jù).復(fù)雜:”管理人 員征服。XP_CmdSheIrdir C o :V"這個(gè)短SQL指令回到客戶文件和文件夾的目錄 在SQL伺候器的c:directory之下，注童這個(gè)例子使用一個(gè)廣大的儲(chǔ)存對(duì)MS SQL伺候器是獨(dú)家的程厚。第二個(gè)功能數(shù)據(jù)庫(kù)伺候器申請(qǐng)部份是他們?nèi)啃枰恍?形式的驗(yàn)證進(jìn)行建立客戶和主機(jī)之間的連接。雖然SQL語(yǔ)言基本語(yǔ)法形式使用中很 容易。他只要建立一些基礎(chǔ)的形式就行了，想要運(yùn)行任何客戶的疑問一定要首先提供 一些形式，這將會(huì)授權(quán)與客戶的國(guó)書，客戶也要有一定的定義請(qǐng)求和回應(yīng)的格式。這 個(gè)連接被一些JS性定

17、義,仰賴客戶的相關(guān)位廈和什么操作系統(tǒng)是在使用中，我們可以 花費(fèi)整個(gè)文章討論例如，DSN連接，較少的DSN連接RDO費(fèi)力和更多的各種不 同的技術(shù)，但是這些主題趙過了這個(gè)文章的范圍。如果你想要學(xué)習(xí)更多有關(guān)他們，一 些Googlelng將會(huì)提供更充足的數(shù)據(jù)給你。然而，下列各項(xiàng)是被包含在關(guān)系中一 些連接請(qǐng)求的一連串的比較通常的項(xiàng)目。數(shù)據(jù)庫(kù)來源、請(qǐng)求類型、數(shù)據(jù)庫(kù)、使 用者身份證、 密碼、任何的連接在連接之前，客戶要連接到什么類型的伺候器。這被一個(gè)提供被需要在正確的格式中產(chǎn)生請(qǐng)求的指令給客戶的軟件成份處理。除了數(shù) 據(jù)庫(kù)的類型，請(qǐng)求類型能用來比較進(jìn)一步定義客戶的請(qǐng)求將會(huì)如何被伺候器處理。下 一個(gè)來數(shù)據(jù)庫(kù)名字

18、和最后證明數(shù)據(jù)。所有的連接信息都很更要，但是顯然量弱的聯(lián) 編是關(guān)于證明數(shù)據(jù)或缺乏。在孫當(dāng)?shù)靥幚砹怂藕蚱鳌Ｃ總€(gè)數(shù)據(jù)庫(kù)明確地用有它的自己 使用者指定了控制他們能運(yùn)行什麼類型的活動(dòng)許可。舉例來說，一個(gè)使用者帳戶會(huì)是 建立如申謂所只有讀哪一對(duì)唯一的通路數(shù)據(jù)Il要。另外的一個(gè)帳戶應(yīng)該作為插入物或 更新，而且也許甚至一個(gè)第三帳戶會(huì)是使用過的因?yàn)閯澇艨刂频倪@個(gè)類型羈定 那個(gè)任何的被妥協(xié)處理的帳戶在功能性中被限制。不幸地，許多數(shù)據(jù)庫(kù)計(jì)畫是建立由 于無效力的或容易的密碼，導(dǎo)致成功的攻擊。書名：MOdem DatabaSe Management作者：Jeffrey A. HOfferI Mary B. Pr

19、escott, Fred R. MCFadden出版社：PrentiCe Hall 2005ISBN: 0131453203 9780131453203指導(dǎo)教師審閱意見:指導(dǎo)教師：年 月 日外文資料DatabaSe Management SyStemS A database (SOmetimeS SPeIIed data base) is also CaIled an electronic database I referring to any COlIeetiOn Of data, Or information, that is specially OrganiZed for rapid S

20、earCh and retrieval by a COmPUter. DatabaSeS are StrUCtUred to facilitate the StOragel retrieval I modification, and deletion Of data in COnjUnCtiOn With VariOUS data-procssing OPeratiOns .Databases Can be StOred On magnetic disk Or tael OPtiCaI disk9 Or SOme Other SeCOndary storage device. A databa

21、se COnSiStS Of a file Or a Set Of files. The information in these files may be broken down into recordsl each Of WhiCh COnSiStS Of One Or more fields. FieldS are the basic UnitS Of data StOrage I and each field typically COntainS information Pertaining to One aspect Or attribute Of the entity descri

22、bed by the database . USing keywords and VariOUS SOrting COmmandSf USerS Can rapidly SearCh I rearrange, grou9 and SeIeCt the fields in many records to retrieve Or Create reports On PartiCUIar aggregate Of data. COmPIeX data relationships and IinkageS may be found in all but the SimPIeSt databases .

23、The SyStem SOftWare PaCkage that handles the difficult tasks associated With Creating ,accessing, and maintaining database records is CaIIed a database management SyStem(DBMS).The PrOgramS in a DBMS PaCkage establish an interface between the database itself and the USerS Of the database. (TheSe USer

24、S may be applications PrOgrammerSy managers and OtherS With information needs, and VariOUS OS programs.) A DBMS Can OrganiZeI PrOCeSSI and PreSent SeIeCted Clata elements form the database. ThiS CaPability enables decision makers to SearChl PrObeV and query database COntentS in Order to extract answ

25、ers to nonrecurring and UnPIanned questions that arn,t available in regular reports. TheSe questions might initially be VagUe and/or POOriy defined IbUt PeOPIe Can UbrOWSe through the database Until they have the needed information. In Shortr the DBMS WiII Umanage the StOred data items and assemble

26、the needed items from the COmmOn database in response to the queries Of those WhO aren5t programmers. A database management SyStem (DBMS) is COmPOSed Of three major PartS:(1 )a StOrage SUbSyStem that StOreS and retrieves data in files;(2) a modeling and manipulation SUbSyStem that PrOVideS the means

27、 With WhiCh to OrganiZe the data and to add f delete, maintain, and UPdate the data;(3)and an interface between the DBMS and its users. SeVeraI major trends are emerging that enhance the VaIUe and USefUIneSS Of database management systems; Managers: WhO require more up-to-data information to make ef

28、fective decision Customers: WhO demand increasingly SOPhiStiCated information SerViCeS and more CUrrent information about the StatUS Of their OrderSy invoices, and accounts. Users: WhO find that they Can develop CUStOm applications With database SyStemS in a fraction Ofthe time it takes to USe tradi

29、tional PrOgramming IangUageS OrggniZRtiOnS : that discover information has a StrategiC value; they UtiliZe their database SyStemS to gain an edge OVer their COmPetitors. The DatabaSe Model A data model describes a Way to StrUetUre and manipulate the data in a database. The StrUetUraI Part Of the mod

30、el SPeCifieS how data ShOUld be represented(SUCh as treel tablesl and SO On ).The manipulative Part Of the model SPeCifieS the OPeratiOn With WhiCh to addf delete, displayl maintain, Printl search, SeIeetI SOrt and UPdate the data. HierarChiCaI MOdeI The first database management SyStemS USed a hier

31、archical model-that is-they arranged records into a tree StrUCtUre. SOme records are root records and all OtherS have UniqUe Parent records. The StrUCtUre Of the tree is designed to reflect the Order in WhiCh the data WiII be USeel that is Ithe record at the root Of a tree WiII be accessed first, th

32、en records One IeVeI below the root fand SO on. The hierarchical model WaS CleVeIOPed because hierarchical relationships are COmmOnly found in business applications. AS you have known, an OrganiZatiOn Char Often describes a hierarchical relationship: top management is at the highest level, middle ma

33、nagement at IOWer IeVelSI and OPeratiOnaI employees at the IOWeSt levels. NOte that Within a Striet hierarchy, each IeVel Of management may have many employees Or IeVelS Of employees beneath itv but each employee has Only One manager. HierarChiCaI data are CharaCteriZed by this one-to-many relations

34、hip among data In the hierarchical approach, each relationship must be explicitly defined When the database is created. EaCh record in a hierarchical database Can COntain Only OrW key field and Only One relationship is allowed between any two fields. ThiS Can create a problem because data do not alw

35、ays COnfOrm to SUCh a StriCt hierarchy. ReIatiOnaI MOdel A major breakthrough in database research OCCUrred in 1970 When E. F. COdd PrOPOSed a fundamentally different approach to database management CaIIed relational model ,which USeS a table as its data structure. The relational database is the mos

36、t WideIy USed database structure. Data is organized into related tables. EaCh table is made UP Of rows CaIIed and COIUmnS CaIled fields. EaCh record COntainS fields Of data about SOme SPeCifiC item. FOr example, in a table COntaining information On employees, a recordwould COntain fields Of data SUC

37、h as a PerSOn5s IaSt name ,first name Iand Street address. StrUetUred query IangUage(SQL)is a query IangUage for manipulating data in a relational database .It is nonprocedural Or declarative, in WhiCh the USer need Only SPeCify an EngliSh-Iike description that SPeCifieS the OPeratiOn and the descri

38、bed rerd Or COmbinatiOn Of rerds. A query OPtimiZer translates the description into a PrOCedUre to PerfOrm the database manipulation NotWOrk MOdel The network model CreateS relationships among data through a Iinked-list StrUetUre in WhiCh SUbOrdinate records Can be Iinked to InOre than One Parent re

39、cord. ThiS approach COmbineS records With IinkSI WhiCh are CaIIed POinterS The POinterS are addresses that indicate the IOCatiOn Of a record. With the network approach, a SUbOrdinate record Can be Iinked to a key record and at the Same time itself be a key record Iinked to Other SetS Of SUbOrdinate

40、records. The network mode historically has had a PerfOrmanCe advantage OVer Other database models. TOday f SUCh PerformanCe CharaeteriStiCS are Only important in high-volume .high-speed transaction PrOCeSSing SUCh as automatic teller machine networks Or airline reservation system. BOth hierarchical

41、and network databases are application specific. If a new application is developed Imaintaining the COnSiStenCy Of databases in different applications Can be Very difficult. FOr example, SUPPOSe a new PenSiOn application is developed .The data are the Samef but a new database must be Createda ObjeCt

42、MOdeI The newest approach to database management USeS an Objeet model I in WhiCh records are represented by entities CaIIed ObjeCtS that Can both StOre data and PrOVide methods Or PrOCedUreS to PerfOrm SPeCifiC tasks The query IangUage USed for the ObjeCt model is the SanIe ObjeCt-Oriented PrOgrammi

43、ng IangUage USed to develop the database application .This Can Create PrObIemS because there is no SimPIe I UnifOrm query IangUage SUCh as SQL . The Objeet model is relatively newl and Only a few examples Of ObjeCt-Oriented database exist. It has attracted attention because developers WhO ChOOSe an

44、Objeet-Oriented PrOgramming language Want a database based On an objoct-orionted model. DiStribUted DatabaSe SimiIarIy I a distributed database is one in WhiCh different PartS Of the database reside On PhySiCaIIy SeParated COmPUters One goal Of distributed databases is the access Of information With

45、OUt regard to where the data might be stored. KeePing in mind that OnCe the USerS and their data are separated , the COmmUniCatiOn and networking COnCePtS COme into PIay . DiStribUted databases require SOftWare that resides PartiaIIy in the Iarger COmPUter. ThiS SOftWare bridges the gap between PerS

46、OnaI and Iarge ComPUterS and resolves the PrObIemS Of incompatible data formats. IdeaIIyl it WOUId make the mainframe databases appear to be Iarge IibrarieS Of information, With most Of the PrOCeSSing accomplished On the PerSOnaI COmPUter. A drawback to SOme distributed SyStemS is that they are Ofte

47、n based On What is CaIIeeI a mainframeentire model I in WhiCh the Iarger host COmPUter is Seen as the master and the terminal Or PerSOnal mputer is Seen as a slave. There are SOme advantages to this approach . With databases Under CentraIiZed COntrOl I many Of the PrObIemS Of data integrity that We

48、mentioned earlier are SOIVed . BUt today9s PerSOnal COmPUterSV departmental mputersl and distributed PrOCeSSing require COmPUterS and their applications to COmmUniCate With each Other On a more equal Or peer-to-peer basis In a database, the Client/server model PrOVideS the framework for distributing

49、 databases. One Way to take advantago Of many COnneeted COmPUterS running database applications is to distribute the application into COOPerating PartS that are independent Of One anther. A Client is an end USer Or COmPUter PrOgram that requests resources across a network. A SerVer is a COmPUter run

50、ning SOftWare that fulfills those requests across a network . When the resources are data in a database fthe Client/server model PrOVideS the framework for distributing database. A file SerVe is SOftWare that PrOVideS access to files across a network. A dedicated file SerVer is a single COmPUter ded

51、icated to being a file server. ThiS is USefUl ,for example Iif the files are Iarge and require fast access Jn SUCh CaSeSt a minicomputer Or mainframe WOUld be USed as a file server. A distributed file SerVer SPreadS the files around On individual COmPUterS instead Of PIaCing them On One dedicated co

52、mputer. AdVantageS Of the Iatter SerVer include the ability to StOre and retrieve files On Other COmPUterS and the elimination Of duplicate files On each COmPUter. A major disadvantage I however, is that individual read/Write requests are being moved across the network and PrObIemS Can arise When UP

53、dating files. SUPPOSe a USer requests a record from a file and ChangeS it WhiIe another USer requests the Same record and ChangeS it too. The SOIUtiOn to this PrObIemS CaIIed record IOCkingI WhiCh means that the first request makes OtherS requests Wait UntiI the first request is SatiSfied . Other US

54、erS may be able to read the record, but they WiII not be able to Change it. A database SerVer is SOftWare that SerViCeS requests to a database across a ntwork. FOr example, SUPPOSe a USer types in a query for data On his Or her PerSOnal COmPUter . If the application is designed With the Client/serve

55、r model in mind Ithe query IangUage Part On the PerSOnaI COmPUter SimPIe SendS the query across the network to the database SerVer and requests to be notified When the data are found. EXamPIeS Of distributed database SyStemS Can be found in the engineering world. SUrVS NetWOrk Filing SyStem(NFS)IfOr

56、 example, is USed in COmPUter-aided engineering applications to distribute data among the hard disks in a network Of SUn WOrkStation. DiStnbUting databases is an evolutionary SteP because it is IOgiCaI that data ShOUld exist at the IOCatiOn Where they are being USed . DePartmentaI COmPUterS Within a

57、 Iarge COrPOratiOn ,for example, ShOUId have data reside IOCaIIy , yet those data ShOUld be accessible by authorized COrPOrate management When they Want to COnSOlidate departmental data . DBMS SOftWare WiII PrOteCt the SeCUrity and integrity Of the database I and the distributed database WiIl appear

58、 to its USerS as no different from the non-distributed database . In this information age, the data SerVer has become the heart Of a company. ThiS One PieCe Of SOftWare COntrOIS the rhythm Of most OrganiZatiOnS and is USed to PUmP information IifebIOOd through the arteries Of the network. BeCaUSe Of

59、 the CritiCaI nature Of this application, the data SerVer is also the One Of the most POPUIar targets for hackers. If a hacker OWnS this application, he Can CaUSe the COmPany,s HheartH to SUffer a fatal arrest. IroniCaIIyy although most USerS are now aware Of hackersl they StiII do not realize how SUSCePtibIe their database SerVerS are to hack attacks. Thus, this article PreSentS a description Of the Primary methods Of attacking database SerVerS (also known as SQL SerVerS) and ShOWS you how to PrOteet yours