外文翻譯----數(shù)據(jù)庫和數(shù)據(jù)倉庫

1、<p>　　Database and Data Warehouses</p><p>　　What is a Database?</p><p>　　What is a database? A database is a collection of related data items. It is generally stored on secondary storage de

2、vices that allow rapid direct access to individual data items. Redundancy is minimized; where possible, only a single copy if a data item exists. The database may be used by many different application systems at once, el

3、iminating the need for separate systems to maintain the data for each application .When a user program inquires if a particular item is in the database, a database </p><p>　　The DBMS cerates the database, ke

4、eps it up-to-date, and provides reday access to authorized user. Database management systems also provide extensive security measures to prevent unauthorized access. They make it convenient for expressing relationship be

5、tween related data items and facilitate the design of user application systems. They provide backup and recovery capabilities to prevent against loss or destruction of vital information. They ensure database integrity, t

6、hat is, what is supposed to</p><p>　　Hierarchical, Network, and Relational Databases (three principal logical database models)</p><p>　　The Hierarchical Model </p><p>　　In a hierar

7、chical database, data records are arranged in a strict parent child relationship. Each parent record may have many children, but each child record has exactly one parent. Figure 3-1 shows a simple hierarchical database,

8、indicating the relationship between a customer and the orders it has placed with a company. Searching a hierarchical database is rapid and convenient as long as it is searched from the top down. IBM’s IMS (Information Ma

9、nagement System) is the most widely used hierarch</p><p>　　The Network Model </p><p>　　The network database model is best at representing many-to-many relationship among data. In other words,

10、a ”child” can have more than one “parent”, as Figure3-2 illustrates. Computer Associates ’IDMS is a network DBMS for computer mainframes.</p><p>　　Network DBMS are more flexible than hierarchical DBMS, but

11、access paths must still be specified in advance. There are practical limitations to the number of links, or relationships ,that can be established among records. If they are too numerous, the software will not work effic

12、iently. Neither network no hierarchical database management models can easily create new relationships among data elements or new patterns of access without major programming efforts.</p><p>　　The Relational

13、 Model </p><p>　　In the early 1970s the relational database approach was developed to provide a much more user-friendly organization. Instead of using complex structures of pointers the relational database

14、 stores information simply as tables called relations. These tables are sometimes called flat because the rows of the table really are very much the same as the records of a file.</p><p>　　Each row in a rela

15、tion is called a record. Each column corresponds to a particular field within the record (fields are also called domains).The fields are headed by attributes, which describe the entries in the column. A relational databa

16、se consists of one or more relations. A relational DBMS performs three primary operations on relations to form new relations:</p><p>　　(1) Two relations may be joined (combined).</p><p>　　(2) A

17、relational may be projected (some of the columns are extracted form the relations and used to form the columns of the new relation).</p><p>　　(3) Records may be selected according to various user specified c

18、riteria’s(Structured Query Language) is the most important query language based on the relational model. For instance, a relation named Accounts, record bank accounts, their balance, and type might look like:</p>

19、<p><b>　　Accounts</b></p><p>　　Heading the columns are the three attributes: Account No, Balance, and Type. Below the attributes are the rows, or records. The first row says that account num

20、ber 173921 has a balance of one thousand and seven hundreds dollars, and it is checking account .Suppose we wanted to know the balance of account 173921.We could ask this Query in SQL as follows:</p><p>　　SE

21、LECT balance FORM Accounts WHERE accountNo=173921</p><p>　　IBM’s DB2 and Oracle from the Oracle Corporation are examples of mainframe relational database management systems. Microsoft Access is a PC relation

22、al database management system. (Oracle also has a PC version).</p><p>　　Client-Server Architecture</p><p>　　Many varieties of modern software use a client-server architecture, in which requests

23、by one process (the client) are sent to another process (the server) for execution. Database systems are no exception. In the simplest client/server architecture, the entire DBMS is a server, except for the query interfa

24、ces than interact with user and send queries or other commands across to the server. For example, relational systems generally use the SQL language for representing requests from the client to t</p><p>　　New

25、 Forms of Database and Data Warehouses</p><p>　　Object-Oriented Database </p><p>　　Object-oriented databases store data as objects that can be automatically retrieved and shared. Included in t

26、he object are the processing instructions to complete each database transaction. These objects can contain various types of data, including sound, graphics, and video as well as traditional data and processing procedures

27、. The objects can be shared and reused. These features of </p><p>　　Object-oriented databases promises to facilitate software development through reuse and the ability to build new multimedia application tha

28、t combine multiple types of data. Benefit of Odom’s is their ability to support application for the World Wide Web, as described in the focus on Technology.</p><p>　　Object-oriented database are still a rela

29、tively new technology and can be much slower than relational systems for handing large quantities of data where there is a high volume of transaction processing. Hybrid object-relational data bases have been developed th

30、at combine the capability of handing large numbers of transactions found in relational Dams with the capability of handing complex relationships and new types of data found in Odom’s.</p><p>　　Hypermedia Dat

31、abase </p><p>　　Hypermedia database manage data differently from object oriented DBMS. but they can also contain diverse types of data. They store data as “chunks”of information, with each chunk in a separ

32、ate node. Each node can contain traditional numeric or character data or wholedocuments ,software programs, graphics, and even full motion video. Each node is totally independent-the nodes are not related by a predetermi

33、ned organization scheme as they are in traditional database. Insured, user establishes thei</p><p>　　Data Warehouses </p><p>　　Many companies have allowed their data to be stored in many separ

34、ate systems that are unable to provide a console dated view of information usable company-wide. One way to address this problem is to build a data warehouse.A data warehouse is a database that consolidates data extracted

35、 from various production and operational systems into one large organization’s core transaction processing systems are reorganized and combined with other information, including historical data so that they can be u</

36、p><p>　　Data dictionary</p><p>　　The data dictionary (Data dictionary) is the record database which and the application procedure Yuan data table of contents one kind of user may visit. The initiat

37、ive data dictionary is refers to when makes the revision to the database or the application program structure, its content may the data dictionary which renews automatically by DBMS. The passive data dictionary is refers

38、 to when the revision must renew its content manually the data dictionary. </p><p>　　The data dictionary is a reservation space, a database, this is uses for the store information database itself. The data d

39、ictionary possibly contains information, for example: The database design material, the storage SQL procedure, the user jurisdiction, the user statistics, in the database process's information database growth statist

40、ics, the database performance statistics, the data character canonical is in the system each kind of data description set, carries on the main achievement which t</p><p>　　The data dictionary usually include

41、s the data item, the construction of data, the data stream, the data storage and the treating processes five parts. The data dictionary is about the data information set, is also all element definition set which contains

42、 to the data flow graph. 　Composes 1 data stream, 2 data stream components, namely the data element 3 data storages 4 process the database the important part is the data dictionaries. It deposits has the related informat

43、ion which the database us</p><p>　　(1) database all pattern object information, like table, view, bunch, and index and so on. Assigns how many spaces, current has used how many spaces and so on. </p>

44、<p>　　(2) row default value. </p><p>　　(3) restraint information integrity. </p><p>　　(4) user's name. the </p><p>　　(5) user and the role the jurisdiction which awards. &l

45、t;/p><p>　　(6) user visit or use audit information. </p><p>　　(7) other produce database information. the database data dictionary is group of tables and the view structure. They deposit in the SYS

46、TEM table space. </p><p>　　The database data dictionary is not only each database center. Moreover to each user is also the very important information. The user may use the SQL sentence to visit the database

47、 data dictionary.</p><p>　　Data Independence, Integrity, and Security</p><p>　　Data Independence </p><p>　　In database system, each program works with its own view or views of the

48、 database. If new fields are added to a database record, the DBMS preserves the existing views so that existing programs don’t have to be changed. The ability to modify the structure of the database without affecting exi

49、sting programs that refer to the database is called data independence</p><p>　　Data Integrity </p><p>　　Data integrity refers to the accuracy, correctness, or validity of the data in the data

50、base. In a database system, data integrity means safeguarding the data against invalid alteration or destruction. In large on-line database system, data integrity becomes a more server problem.</p><p>　　Data

51、 Security </p><p>　　Data security refers to the protection of a database against unauthorized or illegal access or modification. This usually involves one or more level of password protection that is speci

52、fied in the data dictionary. For example, a high-level password might allow a user to read from, write to, and modify the database structure, whereas a low-level password might only allow a user to read from the database

53、.</p><p>　　Usually an audit trail, the recorded history of the modifications to a database, can be used to identify where and when a database was tampered with and it can also be used to restore the file to

54、its original condition. </p><p><b>　　數(shù)據(jù)庫和數(shù)據(jù)倉庫</b></p><p><b>　　1.什么是數(shù)據(jù)庫？</b></p><p>　　數(shù)據(jù)庫就是相關(guān)的數(shù)據(jù)項(xiàng)的集合。它通常被存儲(chǔ)在輔助存儲(chǔ)器上，這些設(shè)備允許快速直接地訪問單個(gè)數(shù)據(jù)項(xiàng)。這樣可以做到冗余最小，如果數(shù)據(jù)項(xiàng)存在的話那

55、么它只有一個(gè)副本。數(shù)據(jù)庫可被很多不同的應(yīng)用系統(tǒng)使用，因而避免了不同的系統(tǒng)為每一個(gè)應(yīng)用而維護(hù)一個(gè)數(shù)據(jù)庫。當(dāng)用戶程序需要數(shù)據(jù)庫中的特殊項(xiàng)時(shí)，數(shù)據(jù)庫土管理系統(tǒng)（DBMS）做實(shí)際的搜索。用戶不需要了解數(shù)據(jù)的存儲(chǔ)格式或數(shù)據(jù)的實(shí)際物理位置。</p><p>　　數(shù)據(jù)庫管理系統(tǒng)建立數(shù)據(jù)庫并不斷更新，為授權(quán)用戶提供方便的訪問方法。數(shù)據(jù)庫管理系統(tǒng)也提供其它的安全措施以防止非授權(quán)訪問。DBMS使用相關(guān)數(shù)據(jù)項(xiàng)之間關(guān)系的表示非常方便，使

56、用戶應(yīng)用系統(tǒng)的設(shè)計(jì)變得容易。它們提供備份和恢復(fù)功能以防止重要的信息丟失或被破壞。由系統(tǒng)管理員決定誰可以訪問數(shù)據(jù)庫、修改數(shù)據(jù)庫以及增加新的關(guān)系等。這也是非常重要的責(zé)任。數(shù)據(jù)庫管理員具有對商業(yè)信息生命線最大的控制權(quán)。數(shù)據(jù)庫管理系統(tǒng)真正的問題是如何組織信息為用戶提出的各種可能的問題提供快速的答案。以不同方式組織的相同數(shù)據(jù)會(huì)產(chǎn)生非常不同的訪問速度。為了表明數(shù)據(jù)項(xiàng)之間的關(guān)系，通常有三種方法用于建立數(shù)據(jù)庫：關(guān)系數(shù)據(jù)庫、層次數(shù)據(jù)庫和網(wǎng)狀數(shù)據(jù)庫。<

57、;/p><p>　　2.層次、網(wǎng)狀和關(guān)系數(shù)據(jù)庫（3個(gè)主要的邏輯數(shù)據(jù)庫模型）</p><p><b>　　(1) 層次模型 </b></p><p>　　在層次數(shù)據(jù)庫中，數(shù)據(jù)記錄按嚴(yán)格的雙親—孩子關(guān)系控制。每一個(gè)雙親記錄可以有許多孩子，但是每一個(gè)孩子只能有一個(gè)雙親。圖3-1所示為一個(gè)簡單的層次數(shù)據(jù)庫，它顯示了顧客和一家公司的定貨關(guān)系。從上到下搜索一個(gè)

58、層次數(shù)據(jù)庫是快捷和方便的。IBM的信息管理系統(tǒng)（IMS）是應(yīng)用最廣泛的層次數(shù)據(jù)庫管理系統(tǒng)。層次數(shù)據(jù)庫管理系統(tǒng)最適合于需要有限個(gè)能夠提前詳細(xì)說明的結(jié)構(gòu)性答案的問題。一旦數(shù)據(jù)關(guān)系被詳細(xì)說明，如果沒有強(qiáng)有力的編程支持，它們是不能輕易被修改的。因此，層次模型不能靈活地滿足信息要求改變的情況。</p><p><b>　　(2) 網(wǎng)狀模型 </b></p><p>　　網(wǎng)狀數(shù)據(jù)

59、庫模型最適宜于表示數(shù)據(jù)之間多對多的關(guān)系。換句話說，“孩子”可以有不止一個(gè)“雙親”，如圖F-2所示。Computer Associate的IDMS就是一個(gè)大型計(jì)算機(jī)的網(wǎng)狀數(shù)據(jù)庫管理系統(tǒng)。</p><p>　　網(wǎng)狀數(shù)據(jù)庫管理系統(tǒng)比層次數(shù)據(jù)庫管理系統(tǒng)更加的靈活，但是訪問路徑仍需提前說明。實(shí)際應(yīng)用中，記錄之間建立的連接或關(guān)系有一些限制。如果關(guān)系太多的話，軟件將不能有效地工作。在不修改主程序的情況下，網(wǎng)狀和層次數(shù)據(jù)庫管理模

60、型都不能容易的在數(shù)據(jù)元素之間建立新的關(guān)系或新的訪問方式。</p><p><b>　　(3) 關(guān)系模型</b></p><p>　　在20世紀(jì)70年代早期發(fā)展關(guān)系數(shù)據(jù)庫是為了提供更多的對用戶友好的組織。關(guān)系數(shù)據(jù)庫簡單地將數(shù)據(jù)存儲(chǔ)為表格（這些表格叫關(guān)系）而沒有采用復(fù)雜的指針結(jié)構(gòu)。這些有時(shí)被稱為平面文件，因?yàn)楸淼男型募挠涗浄浅Ｏ嗨啤?lt;/p><p&

61、gt;　　關(guān)系中的每一行叫一個(gè)記錄。每一列是記錄的一個(gè)特殊的域。域?qū)?yīng)以域名開頭，它描述了整個(gè)一列。關(guān)系數(shù)據(jù)庫包含一個(gè)或多個(gè)關(guān)系。一個(gè)關(guān)系數(shù)據(jù)庫管理系統(tǒng)對關(guān)系進(jìn)行以下三種主要的操作以建立新的關(guān)系。</p><p>　　(1) 連接兩個(gè)關(guān)系（合并）。</p><p>　　(2) 擴(kuò)展一個(gè)關(guān)系（從關(guān)系中抽出某幾列用于形成新的關(guān)系的列）。</p><p>　　(3) 根據(jù)

62、用戶描述的不同標(biāo)準(zhǔn)選擇記錄。</p><p>　　SQL（結(jié)構(gòu)查詢語言）是基于關(guān)系模型的最重要的查詢語言。例如，一個(gè)叫“賬目”的關(guān)系記錄銀行的賬目，它們的結(jié)余和類型如：</p><p>　　列的頭是3個(gè)域名：賬號、結(jié)余、類型。域名以下是行或記錄。第一行說明賬號173921有1700元的結(jié)余，它是檢查賬號。假設(shè)我們想知道賬號173921的結(jié)余，我們可以用SQL發(fā)出請求如下：</p>

63、;<p>　　SELECT balance FORM Accounts WHERE accountNo=173921</p><p>　　IBM的DB2和Oracle公司的Oracle就是大型計(jì)算機(jī)關(guān)系數(shù)據(jù)庫管理系統(tǒng)。Microsoft的Access是個(gè)人計(jì)算機(jī)關(guān)系數(shù)據(jù)庫管理系統(tǒng)。（Oracle也有個(gè)人計(jì)算機(jī)版本）。</p><p>　　3.客戶/服務(wù)器結(jié)構(gòu) &l

64、t;/p><p>　　現(xiàn)代軟件中有很多采用客戶/服務(wù)器結(jié)構(gòu)。在這種結(jié)構(gòu)中一個(gè)過程（客戶）的要求發(fā)送給另一個(gè)過程（服務(wù)器）去處理，數(shù)據(jù)庫系統(tǒng)也不例外。在最簡單的客戶/服務(wù)器結(jié)構(gòu)中，除了查詢接口外整個(gè)數(shù)據(jù)庫管理系統(tǒng)都是服務(wù)器，查詢接口和用戶打交道并且發(fā)送查詢或其他命令給服務(wù)器。例如：關(guān)系系統(tǒng)通常用SQL語言來表示從客戶到服務(wù)器的要求。然后數(shù)據(jù)庫服務(wù)器以表或關(guān)系的形式將答案返回給客戶。當(dāng)答案非常大時(shí)，客戶和服務(wù)器的關(guān)系可能

65、會(huì)變得復(fù)雜。如果同時(shí)有很多數(shù)據(jù)庫用戶，那么服務(wù)器就會(huì)成為瓶頸，因此現(xiàn)在也有一種將更多的工作交給用戶的趨勢。</p><p>　　4.瀏覽器/服務(wù)器結(jié)構(gòu)</p><p>　　B/S（Browser/Server）結(jié)構(gòu)即瀏覽器和服務(wù)器結(jié)構(gòu)。它是隨著Internet技術(shù)的興起，對C/S結(jié)構(gòu)的一種變化或者改進(jìn)的結(jié)構(gòu)。在這種結(jié)構(gòu)下，用戶工作界面是通過WWW瀏覽器來實(shí)現(xiàn)，極少部分事務(wù)邏輯在前端（Bro

66、wser）實(shí)現(xiàn)，但是主要事務(wù)邏輯在服務(wù)器端（Server）實(shí)現(xiàn)，形成所謂三層3-tier結(jié)構(gòu)。這樣就大大簡化了客戶端電腦載荷，減輕了系統(tǒng)維護(hù)與升級的成本和工作量，降低了用戶的總體成本（TCO）。以目前的技術(shù)看，局域網(wǎng)建立B/S結(jié)構(gòu)的網(wǎng)絡(luò)應(yīng)用，并通過Internet/Intranet模式下數(shù)據(jù)庫應(yīng)用，相對易于把握、成本也是較低的。它是一次性到位的開發(fā)，能實(shí)現(xiàn)不同的人員，從不同的地點(diǎn)，以不同的接入方式（比如LAN, WAN, Interne

67、t/Intranet等）訪問和操作共同的數(shù)據(jù)庫；它能有效地保護(hù)數(shù)據(jù)平臺(tái)和管理訪問權(quán)限，服務(wù)器數(shù)據(jù)庫也很安全。</p><p>　　5.數(shù)據(jù)庫的新形式和數(shù)據(jù)倉庫</p><p>　　(1) 面向?qū)ο蟮臄?shù)據(jù)庫</p><p>　　面向?qū)ο蟮臄?shù)據(jù)庫將數(shù)據(jù)作為能自動(dòng)重新得到和共享的對象存儲(chǔ)。包含在對象中的是完成每一項(xiàng)數(shù)據(jù)庫事務(wù)的處理指令。這些對象可能包含不同類型的數(shù)據(jù)，包括

68、傳統(tǒng)的數(shù)據(jù)和處理過程，也包括聲音、圖形和視頻信號等。對象可以共享和重用。面向?qū)ο蟮臄?shù)據(jù)庫的這些特性通過重用和建立新的多媒體應(yīng)用的能力使開發(fā)軟件變得容易，這些應(yīng)用可以將不同類型的數(shù)據(jù)結(jié)合起來。面向?qū)ο髷?shù)據(jù)庫管理系統(tǒng)的好處就是它們支持WWW應(yīng)用的能力。</p><p>　　(2) 超媒體數(shù)據(jù)庫</p><p>　　超媒體數(shù)據(jù)庫管理數(shù)據(jù)的方法與面向?qū)ο髷?shù)據(jù)庫管理系統(tǒng)不同而且它也可能包含不同類型的

69、數(shù)據(jù)。它們將數(shù)據(jù)按信息“塊”存儲(chǔ)，每一塊在一個(gè)單獨(dú)的節(jié)點(diǎn)里。每一個(gè)節(jié)點(diǎn)可能包含傳統(tǒng)的數(shù)字、字符數(shù)據(jù)或整個(gè)文檔、軟件程序、圖形甚至連續(xù)運(yùn)動(dòng)的視頻圖像。每一個(gè)節(jié)點(diǎn)是完全獨(dú)立的——節(jié)點(diǎn)并不像它們在傳統(tǒng)數(shù)據(jù)庫中那樣通過預(yù)先確定的組織方案聯(lián)系起來，而是由用戶自己建立節(jié)點(diǎn)間的連接。節(jié)點(diǎn)間的關(guān)系并不像傳統(tǒng)數(shù)據(jù)庫管理系統(tǒng)那樣結(jié)構(gòu)化，搜索信息也不需按照事先確定好的組織方案，用戶可以直接從一個(gè)節(jié)點(diǎn)到另一個(gè)節(jié)點(diǎn)而不管它們之間是什么關(guān)系。</p>

70、<p><b>　　(3) 數(shù)據(jù)倉庫　</b></p><p>　　很多公司允許他們的數(shù)據(jù)被存在很多開放的系統(tǒng)上，但這些系統(tǒng)不能在公司范圍內(nèi)提供了一個(gè)統(tǒng)一的可用的信息視圖。解決這個(gè)問題的方法是建立一個(gè)數(shù)據(jù)倉庫。數(shù)據(jù)倉庫是一種數(shù)據(jù)庫。它將從不同產(chǎn)品和操作系統(tǒng)調(diào)出的數(shù)據(jù)組合在一起放入這種大型數(shù)據(jù)庫，對管理狀況做出報(bào)告和進(jìn)行分析。這種數(shù)據(jù)庫對源于機(jī)構(gòu)核心事務(wù)處理系統(tǒng)的數(shù)據(jù)進(jìn)行重新組織并

71、與其它信息（包括過去的信息）進(jìn)行合并。這些數(shù)據(jù)可以用來做出管理方面的決策和對管理進(jìn)行分析。在大多數(shù)情況下，數(shù)據(jù)倉庫中的數(shù)據(jù)只可以用來進(jìn)行報(bào)告，不可進(jìn)行更新，所以公司的隱性操作系統(tǒng)的表現(xiàn)就沒有受到影響。數(shù)據(jù)倉庫這種側(cè)重解決問題的特性，使眾多的公司由于運(yùn)用了數(shù)據(jù)倉庫而獲益匪淺。</p><p>　　數(shù)據(jù)倉庫一般都有重新塑造數(shù)據(jù)的能力。關(guān)系數(shù)據(jù)庫的數(shù)據(jù)視圖可以讓用戶從兩個(gè)以上的方面觀察數(shù)據(jù)——例如，按地區(qū)按季度銷售。為

72、了提供這種信息，組織可以用一種特殊化的多維數(shù)據(jù)庫，或用可以在關(guān)系數(shù)據(jù)庫中生成數(shù)據(jù)的多維視圖的工具。多維分析能夠使用戶使用多維的不同方式看到相同的數(shù)據(jù)。信息的每個(gè)方面——生產(chǎn)、定價(jià)、成本、地區(qū)或時(shí)間——都代表不同的維。所以一個(gè)產(chǎn)品經(jīng)理能用多維工具得知六月在西南銷售區(qū)共賣出了多少件，與前一個(gè)月和去年六月相比怎么樣，和銷售預(yù)測相比怎么樣。多維數(shù)據(jù)分析的另外一項(xiàng)是在線分析過程（LOAP）。</p><p><b&g

73、t;　　(4) 數(shù)據(jù)字典 </b></p><p>　　數(shù)據(jù)字典（Data dictionary）是一種用戶可以訪問的記錄數(shù)據(jù)庫和應(yīng)用程序元數(shù)據(jù)的目錄。主動(dòng)數(shù)據(jù)字典是指在對數(shù)據(jù)庫或應(yīng)用程序結(jié)構(gòu)進(jìn)行修改時(shí)，其內(nèi)容可以由DBMS自動(dòng)更新的數(shù)據(jù)字典。被動(dòng)數(shù)據(jù)字典是指修改時(shí)必須手工更新其內(nèi)容的數(shù)據(jù)字典。</p><p>　　數(shù)據(jù)字典是一個(gè)預(yù)留空間，一個(gè)數(shù)據(jù)庫，這是用來儲(chǔ)存信息數(shù)據(jù)庫本身

74、。數(shù)據(jù)字典可能包含的信息，例如： 數(shù)據(jù)庫設(shè)計(jì)資料，儲(chǔ)存的SQL程序，用戶權(quán)限 ，用戶統(tǒng)計(jì)，數(shù)據(jù)庫的過程中的信、數(shù)據(jù)庫增長統(tǒng)計(jì)，數(shù)據(jù)庫性能統(tǒng)計(jì)，數(shù)據(jù)字典則是系統(tǒng)中各類數(shù)據(jù)描述的集合沒，是進(jìn)行詳細(xì)的數(shù)據(jù)收集和數(shù)據(jù)分析所獲得的主要成果。</p><p>　　數(shù)據(jù)字典通常包括數(shù)據(jù)項(xiàng)，數(shù)據(jù)結(jié)構(gòu)，數(shù)據(jù)流，數(shù)據(jù)存儲(chǔ)和處理過程五個(gè)部分。數(shù)據(jù)字典是關(guān)于數(shù)據(jù)的信息的集合，也就是對數(shù)據(jù)流圖中包含的所有元素的定義的集合。組成:1數(shù)據(jù)流

75、2數(shù)據(jù)流分量 即數(shù)據(jù)元素 3數(shù)據(jù)存儲(chǔ) 4處理數(shù)據(jù)庫的重要部分是數(shù)據(jù)字典。它存放有數(shù)據(jù)庫所用的有關(guān)信息，對用戶來說是一組只讀的表。數(shù)據(jù)字典內(nèi)容包括： </p><p>　　(1) 數(shù)據(jù)庫中所有模式對象的信息，如表、視圖、簇及索引等。分配多少空間，當(dāng)前使用了多少空間等。 </p><p>　　(2) 列的缺省值。 </p><p>　　(3) 約束信息的完整性。 &l

76、t;/p><p>　　(4) 用戶的名字。 </p><p>　　(5) 用戶及角色被授予的權(quán)限。 </p><p>　　(6) 用戶訪問或使用的審計(jì)信息。 </p><p>　　(7) 其它產(chǎn)生的數(shù)據(jù)庫信息。 </p><p>　　數(shù)據(jù)庫數(shù)據(jù)字典是一組表和視圖結(jié)構(gòu)。它們存放在SYSTEM表空間中。數(shù)據(jù)庫數(shù)據(jù)字典不僅是每個(gè)

77、數(shù)據(jù)庫的中心。而且對每個(gè)用戶也是非常重要的信息。用戶可以用SQL語句訪問數(shù)據(jù)庫數(shù)據(jù)字典。</p><p>　　6.數(shù)據(jù)的獨(dú)立性、完整性和安全性</p><p>　　(1) 數(shù)據(jù)的獨(dú)立性　</p><p>　　在數(shù)據(jù)庫系統(tǒng)中，每一個(gè)程序處理它自己的視圖或數(shù)據(jù)庫的視圖。如果給數(shù)據(jù)記錄里加了新的域，數(shù)據(jù)庫管理系統(tǒng)就保存已有的視圖以便已有的程序不必改變。修改數(shù)據(jù)庫的結(jié)構(gòu)而不

78、影響已有的引用數(shù)據(jù)庫的程序被稱為數(shù)據(jù)的獨(dú)立性。</p><p>　　(2) 數(shù)據(jù)的完整性</p><p>　　數(shù)據(jù)的完整性是指數(shù)據(jù)庫中的數(shù)據(jù)的精確性、正確性和有效性。在數(shù)據(jù)庫系統(tǒng)中，數(shù)據(jù)的完整性意味著保護(hù)數(shù)據(jù)防止非法修改或破壞。在大型聯(lián)機(jī)數(shù)據(jù)庫系統(tǒng)中，數(shù)據(jù)的完整性更加重要。</p><p>　　(3) 數(shù)據(jù)的安全性　</p><p>　　數(shù)據(jù)