【正文】 February 2022 56Database System Concepts Chapter1 Introduction 167。 Database User and Administrators Database users and user interfacesn Users are differentiated by the way they expect to interact with the system, four categories of users, four categories of interfaces: n naive users – invoke one of the permanent application programs that have been written previouslyn . people accessing database over the web, bank tellers, clerical staffn application programmers – interact with system through DML callsn sophisticated users – form requests in a database query language or tools, and submit these queries to the query processorFebruary 2022 57Database System Concepts Chapter1 Introduction n specialized users – write specialized database applications that do not fit into the traditional data processing framework, Database Administrator (DBA)n The responsibilities of DBA include, but not limited ton schema definitionn schema and physical anization modificationn granting of authorization for data accessn routine maintenancen … 167。 Database User and Administrators (cont.)February 2022 58Database System Concepts Chapter1 Introduction Appendix A Data, Information, Knowledge Definitions in Microsoft Press Computer Dictionaryn data n Plural of datum , an item of informationn Information: n the meaning of the data as it is intended to be interpret by people. Data consist of facts, which bee information as they are seen in context and convey meaning to people. Computer process data without any understanding of what the data representsFebruary 2022 59Database System Concepts Chapter1 Introduction Appendix A Data, Information, Knowledge (cont.) Definitions in Longman Dictionary of Contemporary Englishn data n facts, information n information in a form that can be processed and stored in putersn Information n knowledge in the form of facts and news February 2022 60Database System Concepts Chapter1 Introduction n knowledgen what a person knows。 n the facts, information, skills and understanding that one has gained, esp. through learning or experience Definitions in Cambridge International Dictionary of Englishn Datan information, esp. facts or numbers , collected for examination and used to help decision—makingn or, information in a electronic form that can be processed by putersAppendix A Data, Information, Knowledge (cont.)February 2022 61Database System Concepts Chapter1 Introduction n Informationn knowledge about something , esp. facts and newsn Knowledgen information, esp. facts or numbers , collected for examination and used to help decision—makingn understanding of ,or information about a subject which has been obtained by experience or study, and which is either in a person’s mind or possessed by people generallyAppendix A Data, Information, Knowledge (cont.)February 2022 62Database System Concepts Chapter1 Introduction Appendix AInformation Theory (cont.) n 什么是信息？n 是一種人人皆知的抽象概念，無確切定義，具有兩個(gè)明顯的特征：廣泛性與抽象性。n 廣泛性可從以下三方面來理解n 客觀世界充滿著信息： — 一切客觀物質(zhì)無不具有自己的特征信息。n 人類離不開信息— 人的五官在不停地感知、接收信息；人的神經(jīng)系統(tǒng)在不停地傳遞信息；人的大腦則在不停地處理與決策信息；人與人之間又在不停地交流信息；人活在世上百分之百時(shí)間都在自覺與不自覺地與信息打交道。February 2022 63Database System Concepts Chapter1 Introduction Appendix AInformation Theory (cont.)n 知識(shí)、書本是有用信息的積累n 抽象性則是指n 信息是組成客觀世界并促進(jìn)社會(huì)發(fā)展的三大基本要素之一n 三大要素是：物質(zhì)、能量與信息n 物質(zhì)是基礎(chǔ)，是實(shí)體。n 能量是物質(zhì)運(yùn)動(dòng)的形式， E=mc2，物質(zhì)可轉(zhuǎn)換成能量，而能量 又是改造客觀世界的主要?jiǎng)恿?。February 2022 64Database System Concepts Chapter1 Introduction Appendix AInformation Theory (cont.)n 信息：它依附于物質(zhì)和能量，但又不同于物質(zhì)和能量。沒有信息就不能更好地利用物質(zhì)和能量，人類利用信息和知識(shí)改造物質(zhì)，創(chuàng)造新物質(zhì)，提高能量利用效率，發(fā)現(xiàn)新能量形式。信息也是客觀存在的，它是人類認(rèn)識(shí)、改造客觀世界的主要?jiǎng)恿?，是人類認(rèn)識(shí)客觀世界的更高層次。n 在通信中對(duì)信息的表達(dá)分為三個(gè)層次： 信號(hào)、消息、信息n 信號(hào)：是信息的物理表達(dá)層，是三個(gè)層次中最具體的層次。它是一個(gè)物理量，是一個(gè)載荷信息的實(shí)體，可測(cè)量、可描述、可顯示。February 2022 65Database System Concepts Chapter1 Introduction Appendix AInformation Theory (cont.)n 消息： (或稱為符號(hào) )是信息的數(shù)學(xué)表達(dá)層，它雖不是一個(gè)物理量，但是可以定量地加以描述，它是具體物理信號(hào)的進(jìn)一步數(shù)學(xué)抽象，可將具體物理信號(hào)抽象為兩大類型：離散 (數(shù)字 )消息 , 連續(xù) (模擬 )消息，n 信息：更高層次哲學(xué)上的抽象，是信號(hào)與消息的更高表達(dá)層次。n 三個(gè)層次中，信號(hào)最具體，信息最抽象。它們?nèi)咧g的關(guān)系是哲學(xué)上的內(nèi)涵與外延的關(guān)系n 信息可以認(rèn)為是具體的物理信號(hào)、數(shù)學(xué)描述的消息的內(nèi)涵，即信號(hào)具體載荷的內(nèi)容、消息描述的含義February 2022 66Database System Concepts Chapter1 Introduction Appendix AInformation Theory (cont.)n 信號(hào)是抽象信息在物理層表達(dá)的外延n 消息是抽象信息在數(shù)學(xué)層表達(dá)的外延n 同一信息，可以采用不同的信號(hào)形式 (比如文字、語言、圖象等 )來載荷；同一信息，也可以采用不同的數(shù)學(xué)表達(dá)形式 (比如離散或連續(xù) )來定量描述。同樣，同一信號(hào)形式，比如 “0”與 “1”可以表達(dá)不同形式的信息，比如無與有、斷與通、低與高 (電平 )等等。February 2022 67Database System Concepts Chapter1 Introduction n Data models can be classified as n objectbased data model(基于對(duì)象的數(shù)據(jù)模型 )n recordbased data model(基于記錄的數(shù)據(jù)模型 )n physical data model(物理數(shù)據(jù)模型 )n 基于對(duì)象（ Objectbased）的數(shù)據(jù)模型n 用處： DBS概念設(shè)計(jì)階段，在概念和視圖級(jí)別上描述數(shù)據(jù)，定義 DBS概念 /外模式，生成概念 DBSn 包括： 實(shí)體 — 聯(lián)系模型 、面向?qū)ο螅?objectoriented）數(shù)據(jù)模型n 面向?qū)ο竽Ｐ?: 對(duì)象、對(duì)象類 。 類 = 變量 /屬性 + 方法Appendix B Category of Data ModelFebruary 2022 68Database System Concepts Chapter1 Introduction n 基于記錄的數(shù)據(jù)模型n 用處： DBS邏輯設(shè)計(jì)階段，生成數(shù)據(jù)庫(kù)邏輯模式。與 DBMS相關(guān)，決定了不同的 DBS類型。n 包括： 關(guān)系數(shù)據(jù)模型 、層次型數(shù)據(jù)模型、網(wǎng)狀數(shù)據(jù)模型n 物理數(shù)據(jù)模型n 用處： DBS物理設(shè)計(jì)階段，定義 DBS的 DBS文件的物理存儲(chǔ)結(jié)構(gòu)和存取方法，生成物理數(shù)據(jù)庫(kù)模式。與DBMS和 DBS的實(shí)現(xiàn)相關(guān)。n 包括： Unifying Model、 Frame Memory ModelAppendix B Category of Data Model (cont.)February 2022 69Database System Concepts Chapter1 Introduction Have a breakFebruary 2022 70Database System Concepts Chapter1 Introduction