数据库章节1解读.ppt

Advantages of Database Approach（数据库技术的优势） Minimal data redundancy. Data consistency. Integration of data. Sharing of data. Enforcement of standards. Ease of application development. Uniform security, privacy and integrity. Data independence. * Focus On Data（以数据为核心） Data is most important Data defined first Standard format Access through DBMS Queries, Reports, Forms Application Programs * All Data DBMS Program1 Program2 Queries Reports Base Data Types（数据的表现形式） Numbers Integers Reals Text Length International Date/Time Images Bitmap Vector Sound Samples MIDI Video * Numbers, Text, and Dates Images Sound Video Input Process Output 12 + 8 = 20 000001100 000001000 ---------------- 000010100 20 0010000000000000000 0100000000000001001 0110000011000011011 0111111111111001111 1111111111111011111 1111111111100011111 8 9 20 7 8 19 5 6 15 000001000 000001001 000010100 ..... pitch, volume time 00101010111 11010101010 01010101010 11110100011 00101011011 00101010111 11010101010 01010101010 11110100011 00101011011 00101010111 11010101010 01010101010 11110100011 00101011011 00101010111 11010101010 01010101010 11110100011 00101011011 00101010111 11010101010 01010101010 11110100011 00101011011 Levels of Abstractions in DBMS（DBMS中的数据抽象化） * Example: University database * Data Independency （数据独立性） * Drawbacks of old File methods（文件存储方式的不足） Uncontrolled Duplication Wastes space Hard to update all files Inconsistent data Inflexibility Hard to change data Hard to change programs Limited data sharing Poor enforcement of standards Poor programmer productivity Excessive program maintenance * Example of DBMS vs. File Method (I) A University Database stores the following information： Students Professors Courses Classrooms Who teaches what Who teaches where Who teaches whom * University database: Students: studentID, name, sex, age, grade, class, courseID; Professors: staffID, name, sex, age, courseID, department; Courses: courseID, title, hours, classroomID, schedule; Classrooms: classroomID