數(shù)據(jù)庫管理系統(tǒng)外文翻譯

1、<p>　　Database Management System</p><p>　　Source：Database and Network Journal Author：David Anderson</p><p>　　You know that a data is a collection of logically related data elements that ma

2、y be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals. There’s nothing new about data base-early ones were chiseled in stone, penned on scrolls, and written

3、on index cards. But now database are commonly recorded on magnetically media, and computer programs are required to perform the necessary storage and retrieval operations.</p><p>　　The system software packag

4、e that handles the difficult tasks associated with created, accessing, and maintaining database records is in a DBMS package establish an interface between the database itself and the users of the database. (These users

5、may be applications programmers, managers and others with information needs, and various OS programmers.)</p><p>　　A DBMS can organize, process, and present selected data elements from the database. This cap

6、ability enables decision makers to search. Probe, and query data contents in order to extract answers to nonrecurring and unplanned questions that aren’t available in regular reports. These questions might initially be v

7、ague 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 nee</p><p>　　Special,

8、direct, and other file processing approaches ate used to organize and structure data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquiries fir information. Th

9、is means that the DBMS is able to structure and tie together the logically related data from several large files.</p><p>　　Logical structures. Identifying these logical relationships is a job of the data adm

10、inistrator. A data definition language is used for this purpose. The DBMS may then</p><p>　　Employ one of the following logical structuring techniques during storage access, and retrieval operation: list str

11、uctures, hierarchical (tree) structures, and network structures, relational structures.</p><p>　　1. List structures. In this logical approach, records are linked together by the use of pointers. A pointer is

12、 a data item in one record that identifies the storage location of another logically related record. Records in a customer master file, for example, will contain the name and address of each customer, and an account numb

13、er identifies each record in this file. During an accounting period, a customer may maintain an invoice file to reflect these transactions. A list structure could be used</p><p>　　2. Hierarchical structures.

14、 In this logical approach, data units are structured in multiple levels that graphically resemble an “upside down” tree with the root at the top and the branches formed below, there’s a superior-subordinate relationship

15、in a hierarchical structure. Below the single-root data component are subordinate elements (or one) has only a single owner. Thus, as we see in figure, a customer owns an invoice, and the invoice has subordinate items. T

16、he branches in a tree structure a</p><p>　　3. Network structures. Unlike the tree approach, which dose not permit the connection of branches, the network structure permits the connection of the nodes in a mu

17、ltidirectional manner. Thus, each node may have several owners and may, in turn, own any number of other data units. Data, management software permits the extraction of the needed information from such a structure by beg

18、inning with any record in a file.</p><p>　　4. Relational structures. A relational structure is made up of many tables. The data are stored in the form of “relations” in these tables. For example, relation ta

19、bles could be established to link a college course with the instructor of the course, and with the location of the in order to find the name of the instructor and the location of the English class, the course/instructor

20、relation is searched to get the name, and the course/location relation is searched to get the class location. Many o</p><p>　　5. Physical structure. People visualize or structure data in logical ways for the

21、re</p><p>　　Own purposes. Thus, records R1 and R2 may always be logically linked and processed in sequence in one particular application. However, in a computer system it’s quite possible that these records

22、that are logically contiguous in one application are not physically stored together. Rather, the physical structure of the I/O and storage devices techniques used, but also on the different logical relationships that use

23、rs may assign to the data found on R1 and R2. For example, R1 and R2 may be records o</p><p>　　During the past five years, Microsoft has promoted Data Access Objects (DAO), and then Remote Data Objects (RDO)

24、, and now ActiveX Data Objects (ADO) as the primary data access technology for Visual Basic developers. It seems that Microsoft has been pushing a different data access technology with each successive version of Microsof

25、t Visual Studio. Today, new versions of ADO are available on Microsoft's Web site and ship with other products and technologies, such as Microsoft Windows 2000, Microso</p><p>　　One of the goals of ADO i

26、s to simplify data access. ADO is built upon some fairly complex technologies—OLE DB and ODBC (open database connectivity)—and is designed to allow you to programmatically access and modify data stored in a wide variety

27、of databases. This broad reach is a departure from previous data access technologies. For the sake of comparison, let's take a quick glance at ADO's predecessors: DAO and RDO.</p><p>　　Data Access Ob

28、jects</p><p>　　DAO was originally designed to interact with Microsoft Access databases. Although you can use DAO to access SQL Server and Oracle databases, many developers complain about DAO's performanc

29、e with these large database systems. Others complain that DAO doesn't permit programmers to access some of the richer, more powerful features of SQL Server and Oracle, such as output and return parameters on stored p

30、rocedures.</p><p>　　One of my coworkers likes to say that using DAO to work with an Oracle database is like performing brain surgery on you…without anesthetics…while wearing oven mitts. Extreme? Yes—but he d

31、oes have a point. DAO is tuned to work with desktop databases, not client/server databases. Frustrated by DAO's performance and access limitations, developers who wanted to work with SQL Server and Oracle databases g

32、enerally sought other options.</p><p>　　Remote Data Objects</p><p>　　Microsoft provided another option in RDO, which originally released with Visual Basic 4 Enterprise Edition. RDO's object

33、model closely resembles the hierarchy of structures in the ODBC API. Programmers found that RDO provided much faster access to client/server database systems, such as SQL Server and Oracle, than DAO did. Although those f

34、amiliar with the ODBC API quickly learned how to work with the RDO object model, developers lacking experience with that API, such as those who had been using </p><p>　　The object model itself wasn't the

35、 problem for most programmers learning RDO: the nuances inherited from the ODBC API posed the greatest obstacles. Suddenly, programmers had to bone up on cursors and bookmarks. They had to learn many of the ins and outs

36、of specific database systems. Does the error message "The connection is busy with results from another hstmt" ring any bells out there? If you try to do the impossible on an ODBC connection to your database, RD

37、O won't save you. Instead, you'll ge</p><p>　　Another challenge that RDO posed for programmers accustomed to writing DAO code was that RDO lacked many of DAO's features, such as sorting, searchin

38、g, and filtering. Other DAO functionality unavailable in the RDO world includes data definition language (DDL) interfaces to ODBC API functions such as Create Table and Create Field.</p><p>　　Best of Both Wo

39、rlds: ActiveX Data Objects</p><p>　　Programmers clamored for a data access technology that combined the simplicity and relative ease of use of DAO with the speed, power, and control of RDO. Initially introdu

40、ced as part of the Microsoft Internet Information Server 3 package, ADO was intended to be all things to all people. Of course, such lofty goals are rarely fulfilled.</p><p>　　While the initial release of AD

41、O lacked many of Rod’s features, I believe that ADO 2.0 offered comparable functionality. Certain RDO features, such as mixed cursors, have yet to be implemented in ADO, but these features are few and far between. In fac

42、t, I'm at a loss to name a single significant feature available in RDO that was not available in ADO 2.0 in one form or another. (I'm sure someone will tell me otherwise; a great way to find such features is to m

43、ake a statement like that in a book l</p><p>　　With the release of version 2.1, ADO and its supporting libraries began offering nearly all features available in DAO. DDL libraries were added to ADO in versio

44、n 2.1 to provide functionality similar to functions available with DAO, such as Create Table, Create Field, and Create Index. Microsoft Jet and Replication Objects (JRO) in ADO 2.1 offers much of the Jet-specific functio

45、nality available via the DB Engine object in DAO. ADO 2.1 also added functionality to simplify the retrieval of newly ge</p><p>　　So ADO has most of the functionality of RDO and DAO as well as many helpful f

46、eatures not available in previous data access technologies. </p><p>　　Database Management</p><p>　　There are problems with traditional data management. A more subtle problem is data dependency.

47、When a problem’s logic is tied to it’s physical data structure, changing that structure will almost certainly require changing the program. As a result, programs using traditional access methods can be difficult to maint

48、ain. The solution to both problems id often organizing the data as a single, integrated database. The task of controlling access to all the data can then be concentrated in a centralize</p><p>　　How dose the

49、 use of a centralized database solve the data redundancy problem? All data are collected and stored in a single place; consequently, there is one and only one copy of any given data element. When the value of an element

50、(an address, for example) changes, the single database copy is corrected. Any program requiring access to this data element gets the same value, because there is only one value.</p><p>　　How dose a database

51、help to solve the data dependency problem? Since the responsibility for accessing the physical data rests with the database management system, the programmer can ignore the physical data structure. As a result, programs

52、tend to be much less dependent upon their data, and are generally much easier to maintain. Expect the trend toward database management to continue.</p><p><b>　　數(shù)據(jù)庫管理系統(tǒng)</b></p><p>　　來

53、源：數(shù)據(jù)庫和網(wǎng)絡(luò)雜志</p><p><b>　　作者：大衛(wèi)·安德森</b></p><p>　　眾所周知，數(shù)據(jù)庫是邏輯上相關(guān)的數(shù)據(jù)源集合。這些數(shù)據(jù)源可以按照不同的結(jié)構(gòu)組織起來，以滿足單位和個人的多方面的要求。數(shù)據(jù)庫本身并沒有什么新東西——早期的數(shù)據(jù)庫鑿在石頭上，記在名冊上，以及寫在索引卡中。而現(xiàn)在普遍記錄在可磁化的介質(zhì)上，并且需要用計算機程序來執(zhí)行必須的存

54、儲和檢索操作。</p><p>　　處理與創(chuàng)建、訪問以及維護數(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)管理。DBMS軟件包中的程序在數(shù)據(jù)庫及其用戶間建立接口（這些用戶可以是應(yīng)用程序員）。</p><p>　　DBMS可組織、處理和顯示從數(shù)據(jù)庫選擇的數(shù)據(jù)源。該功能可以是決策者搜索、試探和查詢數(shù)據(jù)庫的內(nèi)容，從而對正式報告中沒有的、不再出現(xiàn)的、且無計劃的問題做出回答。這些問題最初可能是模糊的并

55、且/或者是定義拙劣的，但是人們可以瀏覽數(shù)據(jù)庫知道獲得數(shù)據(jù)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)項來響應(yīng)那些非程序員的詢問。在面向文件的系統(tǒng)中，需要特定的用戶可以將它們的要求傳送給數(shù)據(jù)員，并準(zhǔn)備信息。但是使用DBMS可為用戶提供一個更快的、用戶可選擇的通信方式。</p><p>　　順序的直接的以及其它的文件處理方式通常用于單個文件中的組織和結(jié)構(gòu)，而DBMS可綜合多個文件的

56、數(shù)據(jù)項，并回答某個用戶對信息的查詢。這意味著DBMS能夠訪問和檢索非關(guān)鍵字字段的數(shù)據(jù)，即 DBMS能夠?qū)讉€大文件中邏輯相關(guān)的數(shù)據(jù)組織并聯(lián)在一起。</p><p>　　邏輯結(jié)構(gòu)。確定這些邏輯關(guān)系是數(shù)據(jù)庫管理者的任務(wù)，由數(shù)據(jù)定義語言完成。DBMS在存儲、訪問和檢索操作過程中可以選用的邏輯技術(shù)有：1表結(jié)構(gòu)2層次（樹型）結(jié)構(gòu)3網(wǎng)狀結(jié)構(gòu)4關(guān)系性結(jié)構(gòu)。</p><p>　　1.表結(jié)構(gòu)。在該邏輯方式中

57、，記錄通過指針連接在一起。指針是記錄中的一個數(shù)據(jù)項，它指出另一個邏輯相關(guān)的記錄的存儲位置。例如，顧客主文件中的記錄將包含每個顧客的姓名和地址，而且該文件中的每個記錄都由一個賬號標(biāo)識。在記帳時期，顧客可以在不同時間購買許多東西。因此，公司保存一個發(fā)票文件來反應(yīng)這些交易，這種情況下，可使用表結(jié)構(gòu)顯示任意時間為支付的發(fā)票。顧客文件中的每個記錄都將包含這樣一個記錄，該鏈的最后一個記錄有一個作為指針的特殊字符標(biāo)識。</p><

58、p>　　2.層次結(jié)構(gòu)。該邏輯方式中，數(shù)據(jù)單元的多級結(jié)構(gòu)類似一棵倒立的樹，該樹</p><p>　　的樹根在頂部，而樹枝向下延伸。在層次結(jié)構(gòu)中存在主從關(guān)系，唯一的根數(shù)據(jù)下是從屬的元或節(jié)點，而每個從屬的元或節(jié)點又一次“擁有”一個或多個元或節(jié)點。該結(jié)構(gòu)中根下面的每個元或樹枝都只有一個所有者，這樣一個用戶擁有一個發(fā)票，而發(fā)票又有一個從屬。在樹型結(jié)構(gòu)中，樹枝不能相連。</p><p>　　3.

59、網(wǎng)狀結(jié)構(gòu)。網(wǎng)狀結(jié)構(gòu)不像樹型結(jié)構(gòu)那樣不允許樹枝相連，它允許節(jié)點間多個方向相連。這樣每個節(jié)點都有幾個所有者，而它又可能有任意多個其它數(shù)據(jù)單元。數(shù)據(jù)管理軟件允許從文件的任意記錄開始提取該記錄中的所有信息。</p><p>　　4.關(guān)系型結(jié)構(gòu)。關(guān)系型結(jié)構(gòu)由許多表組成，數(shù)據(jù)則以關(guān)系的形式存儲在這些表中。例如，可以建立一些表將大學(xué)課程與該課程的老師以及上課的地點連接起來。為找到英語課的上課地點和教師名，現(xiàn)查詢課程/教師關(guān)系得

60、到名字，然后再查詢課程/地點關(guān)系得到地點，當(dāng)然也可以得到其它關(guān)系。這是一個新穎的數(shù)據(jù)組織技術(shù)，將來有望得到廣泛應(yīng)用。</p><p>　　5.物理結(jié)構(gòu)：人們總是為了各自的目的，按邏輯方式設(shè)想或組織數(shù)據(jù)。這樣，在一個具體應(yīng)用中，記錄R1和R2是邏輯相連且是按順序處理的。但是，在計算機系統(tǒng)中，這些在一個應(yīng)用中邏輯上鄰接的記錄，物理上完全可能不存儲在一起。即錄在介質(zhì)和硬件中的物理結(jié)構(gòu)不僅取決于用戶定義的R1和R2中的數(shù)

61、據(jù)的邏輯關(guān)系。例如，R1和R2可能是持有信用卡的用戶記錄而用戶要求每兩周將貨物運送到同一個城市的同一個街區(qū)。而從運輸部的管理規(guī)則看，R1和R2是按地理位置組織運輸記錄的順序項。都是在A/R應(yīng)用中，可找到R1和R2表示的顧客，并可根據(jù)其完全不同的賬戶處理它們的賬目。簡言之，在許計算機化的信息記錄中，存儲記錄的物理單元，用戶是看不見的。</p><p>　　關(guān)于數(shù)據(jù)訪問技術(shù)的發(fā)展和最好的數(shù)據(jù)訪問技術(shù)（ADO）<

62、/p><p>　　在過去的五年里，微軟不斷推出開發(fā)人員所用的主要數(shù)據(jù)訪問技術(shù)，首先是Data Access Objects（DAO），然后是Remote Data Objects（RDO），現(xiàn)在是ActiveX Data Objects（ADO）。現(xiàn)在，新版本的ADO已經(jīng)出現(xiàn)在微軟的WEB站點上。ADO的目標(biāo)之一是簡化數(shù)據(jù)訪問。ADO建立在一些相當(dāng)復(fù)雜的技術(shù)上，如OLE Db 和 ODBC（開放式數(shù)據(jù)庫連接），并且

63、是為了能夠?qū)Υ娣庞诤芏喾N不同類型的數(shù)據(jù)庫中的數(shù)據(jù)以編程方式進行訪問和修改而設(shè)計的。正是這種更為廣泛的訪問范圍，使ADO有別于以前的數(shù)據(jù)訪問技術(shù)。為了便于比較，我們首先簡單地看看ADO以前的技術(shù)：DAO 和RDO。</p><p>　　數(shù)據(jù)訪問對象（DAO）</p><p>　　DAO 最初是為了與Microsoft Access 數(shù)據(jù)庫進行交互而設(shè)計的。雖然可以使用DAO訪問SQL Ser

64、ver 和 Oracle 數(shù)據(jù)庫，但是很多開發(fā)人員都抱怨DAO應(yīng)用于這些大型數(shù)據(jù)庫時性能太差。還有人抱怨DAO不允許程序員訪問SQL Server 和 Oracle 的一些更為珍貴的、功能更為前大的性能，例如存儲過程中的輸出和返回參數(shù)等。使用ADO處理Oracle 數(shù)據(jù)庫就相對自己進行腦部外科手術(shù)，不進行麻醉。是的，DAO的設(shè)計意圖是處理桌面數(shù)據(jù)庫的，而不是客戶機/服務(wù)器類型的數(shù)據(jù)庫。由于DAO的性能和訪問局限性令人感到沮喪，因此想要使

65、用SQL Server 和 Oracle 數(shù)據(jù)庫的開發(fā)人員通常尋找其他方法。</p><p>　　遠程數(shù)據(jù)訪問對象（RDO）</p><p>　　微軟提供的另一種選擇是RDO，它最初隨Visual Basic 4企業(yè)版發(fā)行。RDO對象模型與ODBC API中的結(jié)構(gòu)層次非常類似。程序員會發(fā)現(xiàn)與ADO相比，RDO大大提高了對諸如SQL Server 和 Oracle 的客戶機/服務(wù)器類型數(shù)據(jù)庫

66、系統(tǒng)的訪問速度。雖然熟悉ODBC API 的開發(fā)人員會很快學(xué)會如何使用RDO對象模型，但是缺乏使用API經(jīng)驗的開發(fā)人員，比如一直使用DAO的人，則發(fā)現(xiàn)RDO技術(shù)很難使用。</p><p>　　對于大多數(shù)學(xué)習(xí)RDO的程序員而言，對象模型的本身不是問題，而從ODBC API 所繼承而來的細微差別造成了最大的障礙。突然之間，程序員們不得不專心致志于臨時表和書簽。他們必須學(xué)習(xí)特定數(shù)據(jù)庫的很多入口和出口。錯誤消息“The

67、connection is busy with results from another hstmt”是否會在出錯得體放給出提示？基于數(shù)據(jù)庫的ODBC 連接所不能實現(xiàn)的操作，RDO也不會支持。相反的，指揮得到上面的錯誤消息。而DAO則通過自動地創(chuàng)建另外一個數(shù)據(jù)庫連接來執(zhí)行要求的操作，從而隱含了這個問題。</p><p>　　對于習(xí)慣于寫DAO代碼的程序員而言，RDO所帶來的另一個挑戰(zhàn)是RDO 不具備ADO的很多功

68、能，例如排序，查找和過濾等。RDO所不具備的其他DAO功能包括ODBC API 函數(shù)的數(shù)據(jù)定義語言（DDL）接口，例如 Create Table 和 Create Field。</p><p>　　4．最好的數(shù)據(jù)訪問技術(shù)：ActiveX Data Objects</p><p>　　這種數(shù)據(jù)訪問技術(shù)，它能夠把DAO的簡單性和使用上的方便性與RDO的速度、能力和控制相結(jié)合。而最初作為Micr

69、osoft Internet Information Server 3 軟件包一部分出現(xiàn)的ADO，正是希望成為對于所有人都適合的技術(shù)。當(dāng)然，這種理想的目標(biāo)幾乎不可能實現(xiàn)。</p><p>　　雖然 ADO 最初的版本缺少很多RDO 的功能，但是ADO2.0提供了同樣的功能。某些RDO 功能，如混合臨時表，在ADO中還沒有實現(xiàn)，但是這些功能都是很少使用的。事實上，很難找到一個在RDO中非常有用的功能，而在ADO中找

70、不到。</p><p>　　隨著2.1版本的出現(xiàn)，ADO及其支持庫開始提供DAO所具備的幾乎所有功能。在2.1版中加入了DDL庫，以提供類似于DAO中諸如Create Table 、Create Field 和Create Index 等函數(shù)的功能。ADO 2.1中的Microsoft Jet 和 Replication Objects (JRO) 提供在DAO中通過DBEngine 對想實現(xiàn)的Jet特有的大部

71、分功能。ADO2.1還增加了簡化檢索新產(chǎn)生的標(biāo)識值的性能。ADO2.5 并沒有增加使之與DAO和RDO功能更為接近的新功能，這是因為ADO 落后于DAO的唯一方面是其搜索和過濾能力。因此,ADO擁有了RDO 和DAO的絕大多數(shù)功能，同時還有很多以前的數(shù)據(jù)訪問技術(shù)所沒有的有益功能。</p><p><b>　　數(shù)據(jù)庫的管理</b></p><p>　　傳統(tǒng)的數(shù)據(jù)庫管理存

72、在著一些問題，許多問題是由于單獨地考慮應(yīng)用而引起的。較錯綜復(fù)雜是數(shù)據(jù)的依賴性。當(dāng)程序的邏輯結(jié)構(gòu)受到他的物理數(shù)據(jù)結(jié)構(gòu)的束縛的時候，改變了數(shù)據(jù)結(jié)構(gòu)，肯定要改變程序，引出的結(jié)果是采用傳統(tǒng)存取方法的程序很難維護。解決以上問題的方法經(jīng)常是把數(shù)據(jù)組成一體化的數(shù)據(jù)庫，這樣就能把控制存取所有數(shù)據(jù)任務(wù)集中在一個中心的數(shù)據(jù)庫管理系統(tǒng)中。</p><p>　　使用集中化數(shù)據(jù)庫如何解決數(shù)據(jù)冗余問題呢？把所有的數(shù)據(jù)都收集和存放在一個地方，