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(xiàn)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(shí)質(zhì)區(qū)別。</p><p>　　一個(gè)數(shù)據(jù)庫可以被定義成一個(gè)互相聯(lián)系數(shù)據(jù)的集合，

2、這個(gè)集合有很小的復(fù)雜，盡可能的為一個(gè)或多個(gè)應(yīng)用程序在最理想的方式下服務(wù)，存貯數(shù)據(jù)的目的是使他們與用數(shù)據(jù)的程序獨(dú)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(fù)已存在的數(shù)據(jù)，如果一個(gè)系統(tǒng)在結(jié)構(gòu)上完全分離，則他們被稱為一個(gè)數(shù)據(jù)庫集合。</p><p>　　一個(gè)數(shù)據(jù)庫可以設(shè)計(jì)為批處理，實(shí)施處理或連機(jī)數(shù)據(jù)處理，一個(gè)數(shù)據(jù)庫系統(tǒng)包括應(yīng)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(diǎn)之一是他們需要不斷的更新和增加。當(dāng)數(shù)據(jù)類型和應(yīng)用被增加時(shí)，的簡單重構(gòu)必須是可能的，重組織應(yīng)當(dāng)不用重新寫應(yīng)用程序，總體上應(yīng)當(dāng)盡可能是小的變化，這種不費(fèi)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(dú)立這個(gè)術(shù)語經(jīng)常提出作為一個(gè)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(yīng)用程序相互獨(dú)立，目的改變一項(xiàng)時(shí)不用改變另一項(xiàng)，當(dāng)一個(gè)單一的數(shù)據(jù)相集合服務(wù)于不同的應(yīng)用時(shí)，不同的應(yīng)用程序感知

4、數(shù)據(jù)項(xiàng)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(guān)，用于許多應(yīng)用中的在數(shù)據(jù)之間有很多種內(nèi)在的聯(lián)系。</p><p>　　關(guān)于我們所存信息的項(xiàng)是一個(gè)實(shí)體，一個(gè)實(shí)體可以是一個(gè)實(shí)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(gè)真實(shí)的世界，數(shù)據(jù)項(xiàng)代表一個(gè)屬性，該屬性與有關(guān)的實(shí)體聯(lián)合。我們將屬性設(shè)計(jì)成值，一個(gè)屬性有一個(gè)特殊意義。據(jù)此而定義一個(gè)實(shí)體。</p><p>　

5、　計(jì)算機(jī)所用的識(shí)別一個(gè)記錄或一個(gè)元組的一個(gè)屬性或一組屬性，叫做關(guān)鍵字。主關(guān)鍵字定義為能唯一的確定一個(gè)記錄或一個(gè)元組的關(guān)鍵字。一個(gè)實(shí)體識(shí)別符包括一個(gè)或多個(gè)屬性。主關(guān)鍵字是很重要的。因?yàn)樗挥迷谟?jì)算機(jī)中，通過一個(gè)索引和地址算法來找出一個(gè)記錄或一個(gè)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(fù)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(xiàng)之間的關(guān)系。在邏輯上和實(shí)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(gè)模式。</p><p>　　一個(gè)模式是一個(gè)所用數(shù)據(jù)類型的圖表，它給出實(shí)體。屬性和他們之間的特殊的關(guān)系，他是一個(gè)合適的保存數(shù)據(jù)項(xiàng)的框架。</p><p>　　我們必須區(qū)別一個(gè)記錄和一個(gè)記錄的事例，當(dāng)談?wù)摰饺w人員的記錄時(shí)它是一個(gè)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(gè)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(xiàng)類型和記錄類型的總體圖表，子模式項(xiàng)指的是一個(gè)應(yīng)用程序員觀點(diǎn)下的數(shù)據(jù)，許多不同的模式可以從一個(gè)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(shí)服務(wù)于應(yīng)用程序。</p><p>　　一個(gè)數(shù)據(jù)庫管理系統(tǒng)通常是用語同時(shí)處理多個(gè)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(shí)現(xiàn)概念模式的一些細(xì)節(jié)，定義語言是一種高級(jí)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(biāo)庫它必須有豐富的足夠結(jié)構(gòu)以描述真實(shí)世界的有意義的各個(gè)方面，并且必須通過物理模式有能力，自動(dòng)決定概念模式的實(shí)現(xiàn)，必須強(qiáng)調(diào)，當(dāng)一個(gè)數(shù)據(jù)庫處理系統(tǒng)用于建立一個(gè)小數(shù)據(jù)庫中時(shí)，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(zāi)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(guān)系結(jié)構(gòu)，層次結(jié)構(gòu)，網(wǎng)絡(luò)結(jié)構(gòu)</p><p>　　層次型和網(wǎng)絡(luò)型從20世紀(jì)60年代已應(yīng)用于DBMS中，關(guān)系模型在20世紀(jì)70年代早期開始有所介紹。</p><p>　　在關(guān)系模型中，實(shí)體和他們的關(guān)系用二維表格表示，每一個(gè)表

10、格代表一個(gè)實(shí)體，其值是有一定范圍，最終用戶被提供一個(gè)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(dá)，不用表示面向系統(tǒng)的各方面復(fù)雜的情況，關(guān)系數(shù)據(jù)模型似乎用戶所看到的，但不必知道物理的實(shí)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(xì)節(jié)，模型提供了一種高層次的數(shù)據(jù)關(guān)系，然而為了正確的使用關(guān)系數(shù)據(jù)模型，關(guān)系的設(shè)計(jì)必須是完備的和正確的。</p><p>　　盡管一

11、些基于關(guān)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(yīng)用，但它是很難在大規(guī)模范圍內(nèi) 按需求的目標(biāo)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(jìn)已有可能真正回答這個(gè)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(diǎn)和數(shù)值組成，一個(gè)結(jié)點(diǎn)是描述此點(diǎn)上實(shí)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(diǎn)叫做跟結(jié)點(diǎn)。下層的各個(gè)結(jié)點(diǎn)叫子結(jié)點(diǎn)。</p>

12、;<p>　　層次型數(shù)據(jù)結(jié)構(gòu)模型總是從根結(jié)點(diǎn)開始的，第每個(gè)結(jié)包括描述此結(jié)點(diǎn)的一個(gè)或多個(gè)屬性，相關(guān)結(jié)點(diǎn)可以在下一層上，上層的結(jié)點(diǎn)變成新的相關(guān)結(jié)點(diǎn)或父結(jié)點(diǎn)，一個(gè)父結(jié)點(diǎn)可有一個(gè)相關(guān)子結(jié)點(diǎn)或多個(gè)子結(jié)點(diǎn)，層次數(shù)結(jié)點(diǎn)才能存取，許多的關(guān)系只能用笨拙的方法實(shí)現(xiàn)，這常常引起存貯數(shù)據(jù)的復(fù)雜。</p><p>　　網(wǎng)狀數(shù)據(jù)模型將企業(yè)的實(shí)體連接到網(wǎng)絡(luò)中，在網(wǎng)狀數(shù)據(jù)模型中，一個(gè)數(shù)據(jù)庫包括大量區(qū)域，一個(gè)區(qū)域包括一些記錄，而一個(gè)

13、記錄可以包含字段，一個(gè)集合是記錄群，可以在一個(gè)區(qū)域中，或跨越一些區(qū)域，一個(gè)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(shí)生活中發(fā)生得很頻繁的關(guān)系，可以很容易的實(shí)現(xiàn)，網(wǎng)狀數(shù)據(jù)模型是和有復(fù)雜的，應(yīng)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