【正文】 項，并回答某個用戶對信息的查詢。 DBMS 在存儲、訪問和檢索操作過程中可以選用的邏輯技術(shù)有： 1 表結(jié)構(gòu) 2 層次（樹型）結(jié)構(gòu) 3 網(wǎng)狀結(jié)構(gòu) 4 關(guān)系性結(jié)構(gòu)。例如，顧客主文件中的記錄將包含每個顧客的姓名和地址，而且該文件重慶理工 大學(xué) 202。在該邏輯方式中，記錄通過指針連接在一起。 邏輯結(jié)構(gòu) 。在面向文件的系統(tǒng)中，需要特定的用戶可以將它們的要求傳送給數(shù)據(jù)員，并準(zhǔn)備信息。 DBMS 可組織、處理和顯示從數(shù)據(jù)庫選擇的數(shù)據(jù)源。數(shù)據(jù)庫本身并沒有什么新東西 —— 早期的數(shù)據(jù)庫鑿在石頭上，記在名冊上，以及寫在索引卡中。 a great w ay to find such features is to make a statement like that in a book like this.) With the release of version , ADO and its supporting libraries began offering nearly all features available in DAO. DDL libraries w ere added to ADO in version to provide functionality similar to functions available with DAO, such as Create Table, Create F ield, and Create Index. Microsoft Jet and Replication Objects (JRO) in ADO offers much of the Jetspecific functionality available via the DB Engine object in DAO. ADO also added functionality to simplify the 重慶理工 大學(xué) 2021 屆本科生畢業(yè)設(shè)計 (論文 )外文文獻翻譯 19 retrieval of newly generated identity v alues. ADO adds no new functionality to more closely match the capabilities of DAO and RDO, because perhaps the only place w here ADO lags behind DAO is in its searching and filtering capabilities. So ADO has most of the functionality of RDO and DAO as w ell as many helpful features not available in previous data access technologies. Database Management There are problems with traditional data manage ment. A more subtle problem is data dependency. When a problem’s logic is tied to it’s physical data struc ture, changing that structure w ill almost certainly require changing the program. As a result, programs using traditional access methods can be difficult to maintain. The solution to both problems id often anizing the data as a single, integrated databa se. The task of controlling access to all the data can then be concentrated in a centralized database management system. How dose the use of a centralized database solve the data redundancy problem? All data are collected and stored in a single place。ll get that error. DAO hid the problem from you by automatically creating another connection to your database to perform the action you requested. Another challenge that RDO posed for programmers accustomed to writing DAO code was that RDO lacked many of DAO39。s performance and access limitations, developers w ho wanted to w ork with SQL Server and Oracle databases generally sought other options. Remote Data Objects Microsoft provided another option in RDO, w hich originally released with Visual Basic 4 Enterprise Edition. RDO39。s take a quick glance at ADO39。結(jié)果，設(shè)計就可能需要再次構(gòu)想以求得理想的數(shù)據(jù)庫存運行與預(yù)算和進度之間的平衡。比如，當(dāng)討論飾品庫存表和與它相關(guān)的客戶訂單時，就會發(fā)現(xiàn)需要制定一個送貨約束表。 指定實體屬性 一旦設(shè)計者定義了實體間關(guān)聯(lián)，下一步就是去指定每個實體的屬性。 多對多關(guān)聯(lián)： 在多對多關(guān)聯(lián)中，表的一行可能對應(yīng)另一個表的許多行，反之亦然。這種關(guān)聯(lián)類型通常用于子類型數(shù)據(jù)中。意思是對于每個給出的現(xiàn)有實體（即父實體）都有一個或多個現(xiàn)有的另一個實體（即子實體）與之相關(guān)聯(lián)。這個實體被稱作關(guān)系表或交表，其中包含工資水平和部門之間的有效聯(lián)合。 定義實體間的關(guān)聯(lián) 一旦定義了實體，設(shè)計者就能夠繼續(xù)定義每個實體間是如何關(guān)聯(lián)的。實體是人、地方或事物，它們對于整個團體是重要的且需要被記錄在數(shù)據(jù)庫中。 數(shù)據(jù)建模過程包括定義實體、定義實體間關(guān)聯(lián)以及定義每個實體重慶理工 大學(xué) 2021 屆本科生畢業(yè)設(shè)計 (論文 )外文文獻翻譯 11 的屬性的過程。有一種為數(shù)據(jù)庫建模的方式叫作 ERA,它可以表示出實體、實體間的關(guān)聯(lián)和實體的屬性。一個外碼有助于確定表中數(shù)據(jù)的完整性。既然如此， EMP 表中的部門編號列便被看作是與 DEPT 表中相同列對應(yīng)的外碼。 重慶理工 大學(xué) 2021 屆本科生畢業(yè)設(shè)計 (論文 )外文文獻翻譯 10 留意一下 EMP 表中 存儲 的不同數(shù)據(jù)類型：數(shù)值型，字符型或字母型，以及日期型。公司總是希望為每個員工分配一個員工號 ，并目這個號碼必須是每個員工都不同的。同樣也明確了公司董事長的管理人單元為空，因為這個員工不需要向任何人匯報工作。 你會在下面章節(jié)學(xué)到如何設(shè)計數(shù)據(jù)庫，現(xiàn)在讓我們假設(shè)數(shù)據(jù)庫大部分己經(jīng)設(shè)計完成并且有一些表需要被執(zhí)行。 注意：大多數(shù)斯科特 的雇員都是雇自過去的從業(yè)者，他們中有些人在這個領(lǐng)域己經(jīng)有 20 年的經(jīng)驗了。 主碼、數(shù)據(jù)類型和外碼 本篇文章均以假設(shè)的斯科特 表中的一行是一種事物的集合或?qū)嵗?，比如一個員工或發(fā)票上的一項。 表，行和列 在關(guān)系數(shù)據(jù)庫中，一個表（或者說一個關(guān)系）是一個用于保存相關(guān)信息的二維結(jié)構(gòu)。換句話說，關(guān)系數(shù)據(jù)庫有一個 存儲 數(shù)據(jù)的地方，一種創(chuàng)建和檢索數(shù)據(jù)的方法，以及一種確認(rèn)數(shù)據(jù)的邏輯一致性的方法。 some are not. In the widget pany database, there is most likely a relations hip between EMP and DEPT, but depending on the business rules, it is unlikely that the DEPT and SALGRADE entities are related. If the business rules were to restrict certain salary grades to certain departments, there w ould most likely be a new entity that defines the relationship betw een salary grades and departments. This entity would 重慶理工 大學(xué) 2021 屆本科生畢業(yè)設(shè)計 (論文 )外文文獻翻譯 6 be know n as an associative or intersection table and w ould contain the valid binations of salary grades and departments. Associative Table:A database table that stores the valid binations of row s from tw o other tables and usually enforces a business rule. An associative table resolves a manytomany relationship. In general, there are three types of relationships in a relational database: Onetomany The most mon typ e of relationship is onetomany. This means that for each occurrence in a given entity, the parent entity, there may be one or more occurrences in a second entity, the child entity, to w hich it is related. For example, in the widget pany database, the DEPT entity is a parent entity, and for each department, there could be one or more employees associated with that department. The relationship betw een DEPT and EMP is one tomany. Onetoone In a onetoone relationship, a row in a table is related to onl y one or none of the rows in a second table. This relationship type is often used for subtyping. For example, an EMPLOYEE table may hold the information mon to all employees, w hile the FULLTIME, PARTTIME, and CONTRACTOR tables hold information unique to full time employees, parttime employees, and contractors, respectively. These entities would be considered subtypes of an EMPLOYEE and maintain a one toone relationship with the EMPLOYEE table. These relationships are not as mon as one tomany relationships, because if one entity has an occurrence for a corresponding row in another entity, in most cases, the attributes from both entities should be in a single entity. Manytomany In a manytomany relationship, one row of a table may be related to many row s of another table, and vice versa. Usually, w hen this relationship is implemented in the database, a third entity is 重慶理工 大學(xué) 2021 屆本科生畢業(yè)設(shè)計 (論文 )外文文獻翻譯 7 d