數(shù)據(jù)設計外文翻譯

1、<p><b>　　附錄A</b></p><p>　　Data Design </p><p>　　DATA TYPES AND VALUE SETS</p><p>　　Anyone who has ever programmed a computer is accustomed to the fact that you usua

2、lly have to tell the computer 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

3、two integers and another for 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>

4、<b>　　KEYS</b></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

5、 type. For example, if care 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 i

6、ndividual. </p><p>　　An attribute that can be guaranteed to have a unique value for each entity is called a key.Sometimes there may be more than one attribute of an entity that uniquely identifies each occur

7、rence. For example, if the personnel records include Social Security Numbers (and if it is felt that the controls on issuing duplicate Social Security Numbers are adequate), then either Employee Number or Social Security

8、 Number could be used as the key for identifying employees. Keys are fundamental to virtually </p><p>　　DATABASE SCHEMA</p><p>　　This is a description of the data which is stored in the database

9、 and specifies 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

10、to the conceptual 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</

11、p><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

12、 most appropriate for the use to which it is being put. Database sub-schemas have several use : </p><p>　　(1) they can be referred to by application programmers to see what access paths are available in that

13、 part of the database in which they are interested</p><p>　　(2) similarly, they can be referred to by the end-users when they are using a report program generator or formulating queries etc. using a query la

14、nguage provided.</p><p>　　(3) they can be used to divide the database into units for the specification of privacy constrains. For example, a sub-schema could be defined for which all users have read access b

15、ut only one specified user has write (update) access.</p><p>　　PHYSICAL SCHEMA</p><p>　　The physical schema is a description of the physical structure of the database. If, for example, conventio

16、nal 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 constructed as an

17、 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>　　PHYSICAL STORAGE STRUCT

18、URE</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 manipulate these com

19、ponents.</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 failure.</p>

20、<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 intended to support.&l

21、t;/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 question asked i

22、n the analysis:</p><p>　　(1) What data should be captured</p><p>　　(2) How should the data be processed</p><p>　　(3) How should the data be reported</p><p>　　These ques

23、tion 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, report formattin

24、g, 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 might argue t

25、hat 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 today, but is th

26、is 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 forms), and in

27、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 completion on

28、e 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 analysis and creatio

29、n 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.Because they

30、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. This lesso</

31、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 understanding what the

32、 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 resulting desig

33、n 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 understanding that foc

34、using on tasks is necessary. This allows you to approach the analysis of the business from a fresh perspective.</p><p><b>　　附錄B</b></p><p><b>　　數(shù)據(jù)設計</b></p><p&

35、gt;<b>　　數(shù)據(jù)類型和值域</b></p><p>　　任何一個曾經編過程的人都習慣了這樣一個事實：你不得不告訴計算機信息是一個整數(shù)，實數(shù)，字符串，布爾值或其它的值。大多數(shù)計算機由一個整數(shù)加法電路，又有一個實數(shù)加法電路，而且，通常字符串相加當然沒有任何意義。因為在內存中的比特資料可以被解釋成任何一種形式，計算機必須被告訴去做什么。這就是我們熟知的類型。定義資料對象為一個特定的類型對事物

36、內部代表的定義有影響。舉例來說，在大多數(shù)現(xiàn)代計算機框架內部整數(shù)表示為32位比特數(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，可能帶有負號。當一個資料對象被定義為整數(shù)類型時，所有標準的算術和邏輯運算都要做合適的解釋。在定義一個數(shù)據(jù)類型為整形時，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，要定義相對復雜的操作，如排序，是如何進行的。內部表示和外部表示的轉換算法也是必須的。</p><p>

37、<b>　　關鍵詞</b></p><p>　　所有的屬性都描述實體的某一方面。一些屬性扮演附加的角色：從所有其它同一類型的實體事例中區(qū)分某一特定實例。舉個例子，如果我們注意不用一個雇員后標記一個以上的雇員，我們可知一個雇員的雇員號足以固定雇員的其它屬性值。能確保每個實體都有唯一值的屬性叫做關鍵詞。</p><p>　　有時可能不只一個屬性唯一的確定每個實體。舉個例子

38、，如果人事紀錄包含社會安全號（而且認為足以控制社會安全號的重復），那幺雇員號和社會安全號都可作為確定雇員的關鍵詞。關鍵詞在計算機系統(tǒng)中管理資料的所有物理有效方法中是最基本的。當有多余一個的可用關鍵詞時，可供選者的為候選關鍵詞。通常，我們選出一個作為主關鍵詞，并決定紀錄的位置。其它便于檢索的候選關鍵詞被稱為副關鍵詞。</p><p><b>　　數(shù)據(jù)庫模式</b></p><

39、;p>　　用于描述存儲數(shù)據(jù)庫中的數(shù)據(jù)和明確記載數(shù)據(jù)中的數(shù)據(jù)包括什么元素，即這些元素通過怎樣的訪問路徑被訪問。它也包含了安全設置出完整限制之外，與概念模式由幾分相似。但對數(shù)據(jù)的描述將更加真實，一些真實反映由數(shù)據(jù)庫中的數(shù)據(jù)所描述，筆記上，并不能明確記載數(shù)據(jù)庫中的數(shù)據(jù)是如何被存儲及訪問路徑如何被提供。（理想的它是不會參考文件、記錄、設置或其他同類的東西）它是，因此獨立描述及為這結論作為邏輯模式作為參考。</p><p

40、>　　最終用戶或最終用戶組對數(shù)據(jù)庫中的某部分模式特別感興趣被稱為數(shù)據(jù)庫代替-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)庫代替-模式有以下幾種功能：</p><p>　?。?）它們能利用應用程序，使它們所感興趣的內容被訪問的路徑可見。</p><p>　?。?）同樣的，它們可以在最終用戶的使用報告程序發(fā)電機和使用一種查詢語言等等被體現(xiàn)。</p>

41、;<p>　?。?）它們能被用于劃分數(shù)據(jù)單位為按去勸秘密的說明書。例如，代替模式中規(guī)定，每類級別上的用戶可進行那些操作，并不僅指定少數(shù)用戶有修改更新的權利。</p><p><b>　　物理模式</b></p><p>　　物理模式是以物理的結構描述數(shù)據(jù)庫，如果，例如傳統(tǒng)的編入索引的-順序的文件存于數(shù)據(jù)庫中，它將在物理模式中進行說明。它將包含詳細的有按可

42、查格式、塊因素等等物理的模式，這部分構造作為設計所必須的部分進行處理。它也可使用作為完整的部分，它進行操作的部分在以后進行說明。物理的模式有時成內部模式。</p><p><b>　　物理的存儲結構</b></p><p>　　數(shù)據(jù)庫中的結構以被事先在物理結構中定義了存儲結構，它包含幾個典型組件：盤文件，幫起文件，組存儲文件，索引文件及程序操縱等。</p>

43、<p><b>　　支援和恢復系統(tǒng)</b></p><p>　　支援和恢復系統(tǒng)是指在軟件和硬件發(fā)生故障時重建數(shù)據(jù)庫系統(tǒng)。</p><p><b>　　理解應用任務</b></p><p>　　在建造軟件方面經常忽略的步驟之一就是真正理解終端用戶的任務－計算機自動化準備去支持的任務。</p>&l

44、t;p>　　偶爾，這是由于應用本身是專門的；更經常，它是由于傾向于面向數(shù)據(jù)的設計方法。經常地，這些是在分析中主要的問題：</p><p>　?。?）什么數(shù)據(jù)應該被獲取</p><p>　　（2）數(shù)據(jù)怎樣被處理</p><p>　?。?）數(shù)據(jù)怎樣被匯報</p><p>　　這些問題擴展成一系列子問題，并且包括諸如輸入報表，代碼，屏幕布局，

45、計算，存儲容量，處理循環(huán)，報表格式化，分布和維護。這些是所有極其重要的部分。然而一個困難是，他們都單獨集中于數(shù)據(jù)。</p><p>　　人們使用數(shù)據(jù)，但他們做任務。一個可能的爭論是這或許是專業(yè)的工作人員，有權利的人員僅僅將數(shù)據(jù)從輸入報表轉移到鍵盤；他們的任務是非常面向數(shù)據(jù)的。這是今天這些工作的一個清楚地描繪。但這是一個真正要去做的工作的結果，還是計算機應用設計的征兆，使用人類作為輸入設備，特別是大容量的，格式一致

46、的（如報表），并在一個有限可變形范圍內的數(shù)據(jù)，是昂貴和廢棄的，更別說失去人性，獲取數(shù)據(jù)的方法。</p><p>　　這或許聽起來像哲學，但它實際上以應用設計方式輸入。人們使用數(shù)據(jù)，并且他們不通過一次完成來做任務。他們互相做好幾項任務的子集或交集，并且他們并行第一次做完。</p><p>　　設計者允許此觀念指導一項應用的分析和創(chuàng)造，而不是集中于很多年獨領風騷的面向數(shù)據(jù)，就是這種努力的本性有

47、了驚人的改變。為什么Windows環(huán)境如此成功，因為他們允許用戶在小的任務間迅速切換，使它們都存在而不必關閉并退出一個來開始另一個。Windows環(huán)境更近地映射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。這一課不應被丟掉，他應被建立。</p><p>　　理解應用任務意味著遠遠高于識別數(shù)據(jù)元素，使之標準化，創(chuàng)建屏幕，處理數(shù)據(jù)，并且匯報。他意味著真正理解用戶做什么并且他們的任務是什么，并設計響應這