計(jì)算機(jī)專(zhuān)業(yè)畢業(yè)論文外文翻譯--數(shù)據(jù)類(lèi)型和值域

1、<p><b>　　附錄1</b></p><p><b>　　外文翻譯</b></p><p><b>　　數(shù)據(jù)類(lèi)型和值域</b></p><p>　　任何一個(gè)曾經(jīng)編過(guò)程的人都習(xí)慣了這樣一個(gè)事實(shí)：你不得不告訴計(jì)算機(jī)信息是一個(gè)整數(shù)，實(shí)數(shù)，字符串，布爾值或其它的值。大多數(shù)計(jì)算機(jī)由一個(gè)整數(shù)加法電

2、路，又有一個(gè)實(shí)數(shù)加法電路，而且，通常字符串相加當(dāng)然沒(méi)有任何意義。因?yàn)樵趦?nèi)存中的比特資料可以被解釋成任何一種形式，計(jì)算機(jī)必須被告訴去做什么。這就是我們熟知的類(lèi)型。定義資料對(duì)象為一個(gè)特定的類(lèi)型對(duì)事物內(nèi)部代表的定義有影響。舉例來(lái)說(shuō)，在大多數(shù)現(xiàn)代計(jì)算機(jī)框架內(nèi)部整數(shù)表示為32位比特?cái)?shù)的形式。在外部，整數(shù)表現(xiàn)為從0到9的數(shù)字符串的形式，可能帶有負(fù)號(hào)。當(dāng)一個(gè)資料對(duì)象被定義為整數(shù)類(lèi)型時(shí)，所有標(biāo)準(zhǔn)的算術(shù)和邏輯運(yùn)算都要做合適的解釋。在定義一個(gè)數(shù)據(jù)類(lèi)型為整形

3、時(shí)，定義它的整理系統(tǒng)的事件也同樣如此（可能不是如此明顯）。那就是說(shuō)，要定義相對(duì)復(fù)雜的操作，如排序，是如何進(jìn)行的。內(nèi)部表示和外部表示的轉(zhuǎn)換算法也是必須的。</p><p><b>　　關(guān)鍵詞</b></p><p>　　所有的屬性都描述實(shí)體的某一方面。一些屬性扮演附加的角色：從所有其它同一類(lèi)型的實(shí)體事例中區(qū)分某一特定實(shí)例。舉個(gè)例子，如果我們注意不用一個(gè)雇員后標(biāo)記一個(gè)以上

4、的雇員，我們可知一個(gè)雇員的雇員號(hào)足以固定雇員的其它屬性值。能確保每個(gè)實(shí)體都有唯一值的屬性叫做關(guān)鍵詞。</p><p>　　有時(shí)可能不只一個(gè)屬性唯一的確定每個(gè)實(shí)體。舉個(gè)例子，如果人事紀(jì)錄包含社會(huì)安全號(hào)（而且認(rèn)為足以控制社會(huì)安全號(hào)的重復(fù)），那幺雇員號(hào)和社會(huì)安全號(hào)都可作為確定雇員的關(guān)鍵詞。關(guān)鍵詞在計(jì)算機(jī)系統(tǒng)中管理資料的所有物理有效方法中是最基本的。當(dāng)有多余一個(gè)的可用關(guān)鍵詞時(shí)，可供選者的為候選關(guān)鍵詞。通常，我們選出一個(gè)作

5、為主關(guān)鍵詞，并決定紀(jì)錄的位置。其它便于檢索的候選關(guān)鍵詞被稱(chēng)為副關(guān)鍵詞。</p><p><b>　　數(shù)據(jù)庫(kù)模式</b></p><p>　　用于描述存儲(chǔ)數(shù)據(jù)庫(kù)中的數(shù)據(jù)和明確記載數(shù)據(jù)中的數(shù)據(jù)包括什么元素，即這些元素通過(guò)怎樣的訪問(wèn)路徑被訪問(wèn)。它也包含了安全設(shè)置出完整限制之外，與概念模式由幾分相似。但對(duì)數(shù)據(jù)的描述將更加真實(shí)，一些真實(shí)反映由數(shù)據(jù)庫(kù)中的數(shù)據(jù)所描述，筆記上，并不能

6、明確記載數(shù)據(jù)庫(kù)中的數(shù)據(jù)是如何被存儲(chǔ)及訪問(wèn)路徑如何被提供。（理想的它是不會(huì)參考文件、記錄、設(shè)置或其他同類(lèi)的東西）它是，因此獨(dú)立描述及為這結(jié)論作為邏輯模式作為參考。</p><p>　　最終用戶(hù)或最終用戶(hù)組對(duì)數(shù)據(jù)庫(kù)中的某部分模式特別感興趣被稱(chēng)為數(shù)據(jù)庫(kù)代替-模式，理想的，代替-模式將利用字符明確記載數(shù)據(jù)存放位置與最適合的位置，數(shù)據(jù)庫(kù)代替-模式有以下幾種功能：（1）它們能利用應(yīng)用程序，使它們所感興趣的內(nèi)容被訪問(wèn)的路徑可

7、見(jiàn)。（2）同樣的，它們可以在最終用戶(hù)的使用報(bào)告程序發(fā)電機(jī)和使用一種查詢(xún)語(yǔ)言等等被體現(xiàn)。（3）它們能被用于劃分?jǐn)?shù)據(jù)單位為按去勸秘密的說(shuō)明書(shū)。例如，代替模式中規(guī)定，每類(lèi)級(jí)別上的用戶(hù)可進(jìn)行那些操作，并僅僅指定少數(shù)用戶(hù)有修改更新的權(quán)利。</p><p><b>　　物理模式</b></p><p>　　物理模式是以物理的結(jié)構(gòu)描述數(shù)據(jù)庫(kù)，如果，例如傳統(tǒng)的編入索引的-順序的文件存

8、于數(shù)據(jù)庫(kù)中，它將在物理模式中進(jìn)行說(shuō)明。它將包含詳細(xì)的有按可查格式、塊因素等等物理的模式，這部分構(gòu)造作為設(shè)計(jì)所必須的部分進(jìn)行處理。它也可使用作為完整的部分，它進(jìn)行操作的部分在以后進(jìn)行說(shuō)明。物理的模式有時(shí)成內(nèi)部模式。</p><p><b>　　物理的存儲(chǔ)結(jié)構(gòu)</b></p><p>　　數(shù)據(jù)庫(kù)中的結(jié)構(gòu)以被事先在物理結(jié)構(gòu)中定義了存儲(chǔ)結(jié)構(gòu)，它包含幾個(gè)典型組件：盤(pán)文件，幫起文

9、件，組存儲(chǔ)文件，索引文件及程序操縱等。</p><p><b>　　支援和恢復(fù)系統(tǒng)</b></p><p>　　支援和恢復(fù)系統(tǒng)是指在軟件和硬件發(fā)生故障時(shí)重建數(shù)據(jù)庫(kù)系統(tǒng)。</p><p><b>　　理解應(yīng)用任務(wù)</b></p><p>　　在建造軟件方面經(jīng)常忽略的步驟之一就是真正理解終端用戶(hù)的任務(wù)－

10、計(jì)算機(jī)自動(dòng)化準(zhǔn)備去支持的任務(wù)。</p><p>　　偶爾，這是由于應(yīng)用本身是專(zhuān)門(mén)的；更經(jīng)常，它是由于傾向于面向數(shù)據(jù)的設(shè)計(jì)方法。經(jīng)常地，這些是在分析中主要的問(wèn)題：</p><p>　　■什么數(shù)據(jù)應(yīng)該被獲?。?lt;/p><p>　　■數(shù)據(jù)怎樣被處理？</p><p>　　■數(shù)據(jù)怎樣被匯報(bào)？</p><p>　　這些問(wèn)題

11、擴(kuò)展成一系列子問(wèn)題，并且包括諸如輸入報(bào)表，代碼，屏幕布局，計(jì)算，存儲(chǔ)容量，處理循環(huán)，報(bào)表格式化，分布和維護(hù)。這些是所有極其重要的部分。然而一個(gè)困難是，他們都單獨(dú)集中于數(shù)據(jù)。</p><p>　　人們使用數(shù)據(jù)，但他們做任務(wù)。一個(gè)可能的爭(zhēng)論是這或許是專(zhuān)業(yè)的工作人員，有權(quán)利的人員僅僅將數(shù)據(jù)從輸入報(bào)表轉(zhuǎn)移到鍵盤(pán)；他們的任務(wù)是非常面向數(shù)據(jù)的。這是今天這些工作的一個(gè)清楚地描繪。但這是一個(gè)真正要去做的工作的結(jié)果，還是計(jì)算機(jī)應(yīng)用

12、設(shè)計(jì)的征兆？使用人類(lèi)作為輸入設(shè)備，特別是大容量的，格式一致的（如報(bào)表），并在一個(gè)有限可變形范圍內(nèi)的數(shù)據(jù)，是昂貴和廢棄的，更別說(shuō)失去人性，獲取數(shù)據(jù)的方法。</p><p>　　這或許聽(tīng)起來(lái)像哲學(xué)，但它實(shí)際上以應(yīng)用設(shè)計(jì)方式輸入。人們使用數(shù)據(jù)，并且他們不通過(guò)一次完成來(lái)做任務(wù)。他們互相做好幾項(xiàng)任務(wù)的子集或交集，并且他們并行第一次做完。</p><p>　　設(shè)計(jì)者允許此觀念指導(dǎo)一項(xiàng)應(yīng)用的分析和創(chuàng)造，

13、而不是集中于很多年獨(dú)領(lǐng)風(fēng)騷的面向數(shù)據(jù)，就是這種努力的本性有了驚人的改變。為什么Windowsing環(huán)境如此成功？因?yàn)樗麄冊(cè)试S用戶(hù)在小的任務(wù)間迅速切換，使它們都存在而不必關(guān)閉并退出一個(gè)來(lái)開(kāi)始另一個(gè)。Windowing環(huán)境更近地映象人們真正的思維和工作方式而不是老一套的“一次做一件事”的方法。這一課不應(yīng)被丟掉，他應(yīng)被建立。</p><p>　　理解應(yīng)用任務(wù)意味著遠(yuǎn)遠(yuǎn)高于識(shí)別數(shù)據(jù)元素，使之標(biāo)準(zhǔn)化，創(chuàng)建屏幕，處理數(shù)據(jù)，并

14、且匯報(bào)。他意味著真正理解用戶(hù)做什么并且他們的任務(wù)是什么，并設(shè)計(jì)響應(yīng)這些任務(wù)的應(yīng)用，不光是獲取他們關(guān)聯(lián)的數(shù)據(jù)。事實(shí)上，當(dāng)面向與數(shù)據(jù)時(shí)，結(jié)果設(shè)計(jì)會(huì)不可避免地歪曲用戶(hù)的任務(wù)而不是支持他們。</p><p>　　你怎樣設(shè)計(jì)一個(gè)應(yīng)用與任務(wù)而不是數(shù)據(jù)？最大的障礙是簡(jiǎn)單理解集中于必要的任務(wù)。這允許你從一個(gè)新鮮的角度接近事物的分析。</p><p><b>　　附錄2</b><

15、/p><p><b>　　外文原文</b></p><p>　　DATA TYPES AND VALUE SETS</p><p>　　Anyone who has ever programmed a computer is accustomed to the fact that you usually have to tell the compu

16、ter whether the information stored in a particular location is an integer, a real number, a character string, a Boolean va1ue, or whatever. Most computers have one electronic circuit for adding two integers and another f

17、or adding two real numbers, and, of course, addition does not make any sense at all, in general, for character strings. Because the pattern of bits in at storage location ca</p><p><b>　　KEYS</b>&

18、lt;/p><p>　　All attributes describe some aspect of an entity. Some attributes perform the additional role of distinguishing one particular entity occurrence from all others of the same type. For example, if car

19、e is taken not to assign any employee number to more than one person, then knowing an individual's employee number should be sufficient to locate all of the other attribute values for that individual. An attribut

20、e that can be guaranteed to have a unique value for each entity is called a key.Someti</p><p>　　DATABASE SCHEMA</p><p>　　This is a description of the data which is stored in the database and spe

21、cifies what data elements are store and what access paths are provided between these elements. The database schema also contains specifications of privacy as well as integrity constraints. It is somewhat similar to the c

22、onceptual schema, but is a description of data rather than of reality. Some aspects of reality which are described by data in the database schema. Note, however, that the database schema does not specify how</p>&

23、lt;p>　　That part of the database schema which is of interest to a particular end-user or group of end –users is called a database sub-schema. Ideally, a sub-schema should be specified using a notation which is most ap

24、propriate for the use to which it is being put. Database sub-schemas have several use : (ⅰ) they can be referred to by application programmers to see what access paths are available in that part of the database in which

25、they are interested, (ⅱ) similarly, they can be referred to by the end</p><p>　　PHYSICAL SCHEMA</p><p>　　The physical schema is a description of the physical structure of the database. If, for e

26、xample, conventional indexed-sequential files are used to store the database, then this will be stated in the physical schema. It will also contain details of record formats, blocking factors etc. The physical schema is

27、constructed as an essential part of the design process. However, it may also be used as an integeral part of he operational database system as discussed below. The physical schema is sometime</p><p>　　PHYSIC

28、AL STORAGE STRUCTURE</p><p>　　The structure in which the database actually resides is termed the physical storage structure. It typically consists of disc files, tapes, mainstore, indices and programs to man

29、ipulate these components.</p><p>　　BACK-UP AND RECOVERY SYSTEM</p><p>　　The back-up and recovery system is the module which rebuilds the database after corruption due to hardware or software fai

30、lure.</p><p>　　Understanding the Application Tasks</p><p>　　One of the often-neglected steps on building software is really understanding the end user’s job-the that computer automation is inten

31、ded to support.</p><p>　　Occasionally, this is because the application itself is quite specialized; more often, it is because the approach to design tends to be data-oriented. Frequently, these are the major

32、 question asked in the analysis:</p><p>　　■What data should be captured?</p><p>　　■How should the data be processed?</p><p>　　■How should the data be reported?</p><p&g

33、t;　　These question expand into a series of sub question ,and include issues such as input forms, Codes, screen layouts, computations, postings, corrections, audit trails, retention, storage volumes, processing cycles, re

34、port formatting, distribution, and maintenance. there are all vitally important areas. One difficulty, however, is that they all focus solely on data. </p><p>　　People use data, but they do tasks. One

35、 might argue that while this may be true of professional workers. Key-entry clerks really only transfer data from an input form to a keyboard; their tasks are very data-oriented. This is a fair portrayal of their jobs to

36、day, but is this a consequence of the real job that need to get done, or is it a symptom of the computer application? Using humans as input devices, particularly for data that is voluminous, consistent in format (as on f

37、orms), and in a limit</p><p>　　This may sound like so much philosophy, but it has practical import in the way application design is done. People use data, but they do tasks. And they don’t do tasks through o

38、 completion one at a time. They do several tasks that are subset of or in intersection with each other, and they so them all at once, in parallel.</p><p>　　When designers allow this idea to direct the analys

39、is and creation of an Application, rather than focusing on the data orientation that has been historically dominant, the very nature of the effort changes significantly. Why have windowing environments been so successful

40、? Because they allow a user to shut down and exit one in order to begin another. The windowing environment comes closer to mapping the way people really think and work than the old “one thing at a time “approach ever did

41、. This le</p><p>　　Understanding the application tasks means going far beyond identifying the data elements, normalizing them, and creating screens, processing programs, and reports. It means really understa

42、nding what the users do and what their tasks are, and designing the application to be responsive to those tasks, not just to capture the data, associated with them. In fact, when the orientation is toward the data, the r

43、esulting design will inevitably distort the user’s tasks rather than support them.</p><p>　　How do you design an application that is responsive to tasks rather than data? The biggest hurdle is simply underst