数据库技术和应用1TheWorldsofDatabaseSystem.pptVIP

Technology and Application of Database (数据库技术与应用);Technology and Application of Database;Teaching material;Assessment (provisional 暂定);About your major;About?the?tree?of?knowledge;多媒体技术在知识领域的位置;Knowledge in Computer Science;软件层面;Why study ?;A First Course in Database Systems;1 The Worlds of Database Systems;1 The Worlds of Database Systems;;1.1 The Evolution of Database Systems;1.1 The Evolution of Database Systems;1.1 The Evolution of Database Systems;1.1 The Evolution of Database Systems;1.1 The Evolution of Database Systems;A DBMS is expected to: Enable durability(持久存储): the recovery of the database in the face of failures(故障), errors of many kinds, or intentional misuse(故意滥用). Support Data sharing（数据共享）: control access to data from many users at once; without allowing the action of one user to affect other users(isolation/隔离); without actions on the data to be performed partially but not completely(atomicity/原子). ;Database systems evolved from file systems 1. Data redundancy(冗余)and inconsistency(不一致) Multiple file formats, duplication of information in different files. (难以统一/技术垄断考虑) 2. Difficulty in accessing data (访问困难) Need to write a new program to carry out each new task. ;Database evolved from file systems (cont.) 3. Integrity(完整性) problems Integrity constraints(约束) (e.g. account balance 0) become “buried(埋入)” in program code rather than being stated explicitly(明确地).Hard to add new constraints or change existing ones. 4. Atomicity of updates(原子性操作) Failures may leave database in an inconsistent state with partial updates carried out. Example: Transfer of funds(资金) from one account to another should either complete or not happen at all.;Database evolved from file systems (cont.) 5.Concurrent(并发)access by multiple users Uncontrolled concurrent accesses can lead to inconsistencies. Example: Two people reading a balance and updating it at the same time. 6. Security problems Hard to provide user access to some, but not all, data. (不同用户的不同权限) ;Late 1960s and