【正文】 庫開發(fā)實例精粹 》 ，電子工業(yè)出版社發(fā)行，2022 年 5 月出版[6] 網(wǎng)冠科技編著： 《vbscript 時尚編程百例》 ，機械工業(yè)出版社， 2022 年 11月出版[7] 趙豐年編著： 《javascript 實例教程》 ，電子工業(yè)出版社，2022 年 1 月出版[8] 潘郁編著 :《電子商務(wù)數(shù)據(jù)庫技術(shù) 》 ，北京大學(xué)出版社,2022 年出版[9] 張海藩編著： 《軟件工程導(dǎo)論》 ，清華大學(xué)出版社 1998 年出版。大多數(shù)數(shù)據(jù)庫的最主要特點之一是他們需要不斷的更新和增加。我們將屬性設(shè)計成值，一個屬性有一個特殊意義。一個實體識別符包括一個或多個屬性。在邏輯上和篁上描述數(shù)據(jù)是不同的。我們必須區(qū)別一個記錄和一個記錄的事例，當(dāng)談?wù)摰饺w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。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(dāng)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(zāi)難性的。盡管一些基于關(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)改進已有可能真正回答這個問題。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(guān)結(jié)點可以在下一層上，上層的結(jié)點變成新的相關(guān)結(jié)點或父結(jié)點，一個父結(jié)點可有一個相關(guān)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(guān)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(fù)雜。 a mon 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 structure.At abase may be designed for batch processing, realtimes processing, or inline processing. a data base system involves application program, DBMS and database.One o he most 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.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 on the rate at which dataprocessing application can be developed in a corporation.The term data independence is often quoted as being one of the main attributes of a database int implies that the data 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 extent database anization is concerned with the as how and where the data are stored a database used for many applications can have multiple interconnection referred to as entities an entity may be a tangible object or no tangible if it has various properties which we may wish to record it can describe the real world the data item represents an attribute and the attribute must be associated which the relevant entity we relevant entity we design values to the attributes one attribute has a special significance in that it identifies the entity.The logical database description 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 dataitems can be fitted.We must distinguish between a record type and a instance of the dataitem 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 be derived from one schema.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 operations. A dams will usually be handling multiple data calls concurrently, it must anize its system buffers so that different data operations can be in process together, it provides a data definition 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 model”.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 automatically 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 inefficient implementation can be disastrous.Logical schemas are defined as data, pedals with the underlying structure of particular database management systems superimposed on them at the present time there are three main underlying structures for database management systems these are:.relational .hierarchical .workThe hierarchical and work structures have been used for dams since the 1960’s . the relational structure was introduced in the early 1970’s.In the relational model twodimensional tables represent the entities and their relationships every table represents an entities are represented by mon columns containing values from a domain or range of possible values .The end user is presented with a simple data model his and her request and don not reflect any plexities due to systemoriented aspects a relational data model is what the user sees , but it is mot necessarily what will be implemented physically.The relational data model removes the details of storage structure and access strategy from the user interface the model providers a relatively higher degree of datato make use of this property of the relational data model however, the design of the relations must be plete and accurate.Although some dams based on the relational data model are mercially available today it is difficult to provide a plete 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.The hierarchical data model is based no