外文翻譯---網(wǎng)站基層---------數(shù)據(jù)庫系統(tǒng)

1、<p><b>　　附錄2</b></p><p><b>　　英文文獻譯文</b></p><p>　　網(wǎng)站基層---------數(shù)據(jù)庫系統(tǒng)</p><p>　　用于描述文件和數(shù)據(jù)庫的概念相同結(jié)構(gòu)中有各種各樣的實質(zhì)區(qū)別。</p><p>　　一個數(shù)據(jù)庫可以被定義成一個互相聯(lián)系數(shù)據(jù)的集合，

2、這個集合有很小的復雜，盡可能的為一個或多個應用程序在最理想的方式下服務，存貯數(shù)據(jù)的目的是使他們與用數(shù)據(jù)的程序獨立，一種相同的控制方法用在數(shù)據(jù)庫內(nèi)更新數(shù)據(jù)和修改，恢復已存在的數(shù)據(jù)，如果一個系統(tǒng)在結(jié)構(gòu)上完全分離，則他們被稱為一個數(shù)據(jù)庫集合。</p><p>　　一個數(shù)據(jù)庫可以設計為批處理，實施處理或連機數(shù)據(jù)處理，一個數(shù)據(jù)庫系統(tǒng)包括應用程序，數(shù)據(jù)庫管理系統(tǒng)和數(shù)據(jù)庫。</p><p>　　大多數(shù)數(shù)

3、據(jù)庫的最主要特點之一是他們需要不斷的更新和增加。當數(shù)據(jù)類型和應用被增加時，的簡單重構(gòu)必須是可能的，重組織應當不用重新寫應用程序，總體上應當盡可能是小的變化，這種不費力的改變數(shù)據(jù)庫將在數(shù)據(jù)處理的速度上產(chǎn)生很大的影響。</p><p>　　數(shù)據(jù)獨立這個術(shù)語經(jīng)常提出作為一個數(shù)據(jù)主要屬性之一，它是指數(shù)據(jù)和使用數(shù)據(jù)的應用程序相互獨立，目的改變一項時不用改變另一項，當一個單一的數(shù)據(jù)相集合服務于不同的應用時，不同的應用程序感知

4、數(shù)據(jù)項與記錄之間的管理說明有聯(lián)系，也和數(shù)據(jù)是怎樣存貯的和存在那里有關，用于許多應用中的在數(shù)據(jù)之間有很多種內(nèi)在的聯(lián)系。</p><p>　　關于我們所存信息的項是一個實體，一個實體可以是一個實在的物體或抽象的事物，它有我們希望記錄的各種性質(zhì)，它能描述一個真實的世界，數(shù)據(jù)項代表一個屬性，該屬性與有關的實體聯(lián)合。我們將屬性設計成值，一個屬性有一個特殊意義。據(jù)此而定義一個實體。</p><p>　

5、　計算機所用的識別一個記錄或一個元組的一個屬性或一組屬性，叫做關鍵字。主關鍵字定義為能唯一的確定一個記錄或一個元組的關鍵字。一個實體識別符包括一個或多個屬性。主關鍵字是很重要的。因為它被用在計算機中，通過一個索引和地址算法來找出一個記錄或一個元組。</p><p>　　如果數(shù)據(jù)庫的作用僅僅是存貯數(shù)據(jù)，那它的結(jié)構(gòu)將是簡單的，大多數(shù)復雜性起因于數(shù)據(jù)必須所表現(xiàn)所存貯各種各樣的數(shù)據(jù)項之間的關系。在邏輯上和實際上描述數(shù)據(jù)是

6、不同的。</p><p>　　邏輯數(shù)據(jù)庫的描述叫做一個模式。</p><p>　　一個模式是一個所用數(shù)據(jù)類型的圖表，它給出實體。屬性和他們之間的特殊的關系，他是一個合適的保存數(shù)據(jù)項的框架。</p><p>　　我們必須區(qū)別一個記錄和一個記錄的事例，當談論到全體人員的記錄時它是一個真正的記錄類型，而不是與它相結(jié)合的數(shù)據(jù)值。</p><p>　　

7、一個模型用于描述數(shù)據(jù)庫中的所用存貯在數(shù)據(jù)庫中的數(shù)據(jù)項類型和記錄類型的總體圖表，子模式項指的是一個應用程序員觀點下的數(shù)據(jù)，許多不同的模式可以從一個模式中得到。</p><p>　　模式和子模式是由數(shù)據(jù)庫管理系統(tǒng)使用的，數(shù)據(jù)庫管理系統(tǒng)的主要作用是執(zhí)行數(shù)據(jù)操作時服務于應用程序。</p><p>　　一個數(shù)據(jù)庫管理系統(tǒng)通常是用語同時處理多個數(shù)據(jù)調(diào)用，它必須組織系統(tǒng)緩沖使不同的數(shù)據(jù)操作能夠一起處理，

8、它提供種數(shù)據(jù)定義語言經(jīng)指定概念模式很可能還包括用物理模式實現(xiàn)概念模式的一些細節(jié)，定義語言是一種高級語言，能夠讓你描述概念模型，術(shù)語為數(shù)據(jù)模型。</p><p>　　數(shù)據(jù)模型選擇是很困難的，圖標庫它必須有豐富的足夠結(jié)構(gòu)以描述真實世界的有意義的各個方面，并且必須通過物理模式有能力，自動決定概念模式的實現(xiàn)，必須強調(diào)，當一個數(shù)據(jù)庫處理系統(tǒng)用于建立一個小數(shù)據(jù)庫中時，許多數(shù)據(jù)庫包括了上萬字節(jié)，所以無效的執(zhí)行可能是災難性的。&

9、lt;/p><p>　　邏輯模式被定義為數(shù)據(jù)模式，帶有附加在其上的特別折數(shù)據(jù)庫管理系統(tǒng)的基本結(jié)構(gòu)，目前，數(shù)據(jù)庫管理系統(tǒng)有，三種主要的基本結(jié)構(gòu)，他們是：關系結(jié)構(gòu)，層次結(jié)構(gòu)，網(wǎng)絡結(jié)構(gòu)</p><p>　　層次型和網(wǎng)絡型從20世紀60年代已應用于DBMS中，關系模型在20世紀70年代早期開始有所介紹。</p><p>　　在關系模型中，實體和他們的關系用二維表格表示，每一個表

10、格代表一個實體，其值是有一定范圍，最終用戶被提供一個簡單數(shù)據(jù)模型，他或她需求由信息內(nèi)容的描述而明確的表達，不用表示面向系統(tǒng)的各方面復雜的情況，關系數(shù)據(jù)模型似乎用戶所看到的，但不必知道物理的實現(xiàn)。</p><p>　　數(shù)據(jù)模型在用戶截面上排出了存貯結(jié)構(gòu)和存取策略的細節(jié)，模型提供了一種高層次的數(shù)據(jù)關系，然而為了正確的使用關系數(shù)據(jù)模型，關系的設計必須是完備的和正確的。</p><p>　　盡管一

11、些基于關系數(shù)據(jù)模型的數(shù)據(jù)庫管理系統(tǒng)今天以商業(yè)化的應用，但它是很難在大規(guī)模范圍內(nèi) 按需求的目標提供一套完整的操作能力，今天在提供快速且穩(wěn)定的硬件方面的技術(shù)改進已有可能真正回答這個問題。</p><p>　　層次型數(shù)據(jù)模型是基于數(shù)型結(jié)構(gòu)的，由結(jié)點和數(shù)值組成，一個結(jié)點是描述此點上實體屬性的數(shù)據(jù)集合。</p><p>　　層次樹結(jié)構(gòu)的最頂層結(jié)點叫做跟結(jié)點。下層的各個結(jié)點叫子結(jié)點。</p>

12、;<p>　　層次型數(shù)據(jù)結(jié)構(gòu)模型總是從根結(jié)點開始的，第每個結(jié)包括描述此結(jié)點的一個或多個屬性，相關結(jié)點可以在下一層上，上層的結(jié)點變成新的相關結(jié)點或父結(jié)點，一個父結(jié)點可有一個相關子結(jié)點或多個子結(jié)點，層次數(shù)結(jié)點才能存取，許多的關系只能用笨拙的方法實現(xiàn)，這常常引起存貯數(shù)據(jù)的復雜。</p><p>　　網(wǎng)狀數(shù)據(jù)模型將企業(yè)的實體連接到網(wǎng)絡中，在網(wǎng)狀數(shù)據(jù)模型中，一個數(shù)據(jù)庫包括大量區(qū)域，一個區(qū)域包括一些記錄，而一個

13、記錄可以包含字段，一個集合是記錄群，可以在一個區(qū)域中，或跨越一些區(qū)域，一個集合類型基于所有者的記錄類型和成員記錄類型，許多在真實生活中發(fā)生得很頻繁的關系，可以很容易的實現(xiàn)，網(wǎng)狀數(shù)據(jù)模型是和有復雜的，應用程序員必須很熟悉數(shù)據(jù)庫的邏輯結(jié)構(gòu)。</p><p><b>　　附錄3</b></p><p><b>　　外文資料譯文</b></p>

14、;<p>　　Database system</p><p>　　The conception sued for describing files and databases has varied substantially in the same organization.</p><p>　　A database may be defined as a collectio

15、n of interrelated data stored together with as little redundancy as possible to serve one or more applications in an optimal fashion; the data are stored so that they are independents of programs which use the data; a co

16、mmon and controlled approach is used in adding new data and in modifying and retrieving existing data within the data base one system is said to contain a collection of databases if they are entirely separate in structur

17、e.</p><p>　　At abase may be designed for batch processing, real-times processing, or in-line processing. a data base system involves application program, DBMS and database.</p><p>　　One o he mos

18、t important characteristic of most databases is that they will constantly need to change and grow easy restructuring of the database must be possible as new data types and new applications are added.</p><p>

19、　　The restructuring should be possible without having to rewrite the application program and in general should cause as little upheaval as possible the ease with which a database can be changed will have a major effect o

20、n the rate at which data-processing application can be developed in a corporation.</p><p>　　The term data independence is often quoted as being one of the main attributes of a database int implies that the d

21、ata and the may be changed without changing the other, when a single setoff data items serves a variety of applications, different application programs perceive different relationships between the data items, to a large

22、extent database organization is concerned with the as how and where the data are stored a database used for many applications can have multiple interconnection refer</p><p>　　The logical database description

23、 id referred to as a schema. The names of the entities and attributes and specifics the relations between them .It is a framework into which the values of the data-items can be fitted.</p><p>　　We must disti

24、nguish between a record type and a instance of the data-item types and record types stored in a database the term subschema refers to an collocation programmer’s vies of the data he uses. Many different sub subschema can

25、 be derived from one schema.</p><p>　　The schema and the subschema are both used by the database management system the primary function of which is to serve the application programs by execution their data o

26、perations. </p><p>　　A dams will usually be handling multiple data calls concurrently, it must organize its system buffers so that different data operations can be in process together, it provides a data def

27、inition language to specify the conceptual schema and most likely some of the details regarding the implementation of the conceptual schema by the physical schema the describe the conceptual schema in terms for a “data m

28、odel”.</p><p>　　The choice of a data model is a difficult one, since it must be such enough in structure to describe significant aspects of the real world, yet it must be possible to determine fairly automat

29、ically an efficient implementation of the conceptual conceptual schema by a physical schema it should be emphasized that while a dims might be used to build small databases many databases involve millions of bytes and an

30、 inefficient implementation can be disastrous.</p><p>　　Logical schemas are defined as data, pedals with the underlying structure of particular database management systems superimposed on them at the present

31、 time there are three main underlying structures for database management systems these are:</p><p>　　.relational .hierarchical .network</p><p>　　The hierarchical and network structures

32、 have been used for dbms since the 1960’s . the relational structure was introduced in the early 1970’s.</p><p>　　In the relational model two-dimensional tables represent the entities and their relationships

33、 every table represents an entities are represented by common columns containing values from a domain or range of possible values.</p><p>　　The end user is presented with a simple data model his and her requ

34、est and don not reflect any complexities due to system-oriented aspects a relational data model is what the user sees , but it is mot necessarily what will be implemented physically.</p><p>　　The relational

35、data model removes the details of storage structure and access strategy from the user inter-face the model providers a relatively higher degree of data</p><p>　　to make use of this property of the relational

36、 data model however, the design of the relations must be complete and accurate.</p><p>　　Although some dbms based on the relational data model are commercially available today it is difficult to provide a co

37、mplete set of operational capabilities with required efficiency on a large scale it appears today that technological improvements in providing faster and more reliable hardware may answer the question positively.</p&g

38、t;<p>　　The hierarchical data model is based no a tree-like structure made up of nodes and branches a node is a collection of data attributes describing the entity at that opint the highest node of the hierarchica

39、l tree structure is called a root the nodes at succeeding lower levels are called children.</p><p>　　A hierarchical data model always starts with a root node every node consists of one or more attributes des

40、cribing the entity at that node dependent nodes can follow the succeeding levels the mode in the receding level becomes the parent node of the new dependent nodes a parent node can have one child node as a dependent or m

41、any children nodes the major advantage of the hierarchical data model is the existence of proven database management systems that use the hierarchical data model as the basic</p><p>　　The network data model

42、interconnects the entities of an enterprise into a network in the network data model a database.</p><p>　　Consists of a number of areas an area contains records in turn a recode may consist of fields a set w

43、hich is a grouping of records may reside in an area or span a number of areas a set type is based on the owner record type and the member record type the many-to-many relation-ship which occurs quite frequently in rap fi