计算机科学概论第九章

9-9
LOGO
Figure 9.3 A relation containing employee information 图9.3 包含员工信息的一个关系
9-10
LOGO
Relational Design关系设计 关系设计 Avoid multiple concepts within one relation避 免一个关系中有多个概念
DBMS will mask this organizational detail from its users数据库管理系统掩饰了用户端数据如何存放的细 节 Data independence: The ability to change the organization of a database without changing the application software that uses it 数据独立性：改变数 据库组织本身而不改变应用软件的能力
Lossless or nonloss decomposition: A “correct” decomposition that does not lose any information 无损分解：把一个关系分解成几个比较小的关系时 ，信息有时不会丢失，这种分解称为无损分解
9-12
LOGO
Figure 9.4 A relation containing redundancy 图9.4 包含冗余的关系
Example: transferring money between bank accounts 例：将钱从银行账户里取出
9-15
LOGO
Figure 9.7 A relation and a proposed decomposition 图9.7 关系和提议的分解
9-16
LOGO
Relational Operations关系运算 关系运算 Select: Choose rows 选择行 Project: Choose columns 选择列 Join: Assemble information from two or more relations将两个或多个关系中的信息连接起来
9-22
LOGO
Structured Query Language (SQL)结构化查询语言 结构化查询语言
Operations to manipulate tuples对元组一些操 作
Insert 插入 Update更新 Delete删除 Select选择
9-23
LOGO
SQL Examples SQL例子 例子 select EmplId, Dept from ASSIGNMENT, JOB where ASSIGNMENT.JobId = JOB.JobId and ASSIGNMENT.TermData = “*” insert into EMPLOYEE values (‘43212’, ‘Sue A. Burt’, ’33 Fair St.’, ‘444661111’)
9-6
LOGO
Database Management Systems 数据库管理系统
Database Management System (DBMS): A software layer that manipulates a database in response to requests from applications数据库管 理系统：用来处理用户的请求活动的软件层 Distributed Database: A database stored on multiple machines分布式数据库：一个存储在多 台机器里的数据库
9-24
LOGO
SQL Examples (continued) SQL例子 例子 delete from EMPLOYEE where Name = ‘G. Jerry Smith’ update EMPLOYEE set Address = ‘1812 Napoleon Ave.’ where Name = ‘Joe E. Baker’
Chapter 9:Database Systems 第九章： 第九章：数据库系统
Computer Science: An Overview Tenth Edition
by J. Glenn Brookshear
Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
9-26
LOGO
Figure 9.13 The associations between objects in an object-oriented database图9.13 面向对象数据库中对象间的关联 图
wk.baidu.com
9-27
LOGO
Advantages of Object-oriented Databases 面向对象数据库的优点
9-13
LOGO
Figure 9.5 An employee databaseconsisting of three relations图9.5 由三个关系组成的员工数据库 图
9-14
LOGO
Figure 9.6 Finding the departments in which employee 23Y34 has worked 图9.6 查找员工 查找员工23Y34工作过的部门 工作过的部门
Example: multimedia例如：多媒体
9-28
LOGO
Maintaining Database Integrity维护数据库的完整性 维护数据库的完整性
Transaction: A sequence of operations that must all happen together事务：必须同时发生的一系列 操作
9-5
LOGO
Schemas 模式 Schema: A description of the structure of an entire database, used by database software to maintain the database模式：是整个数据库结 构的一个描述，数据库软件用它来维护数据库 Subschema: A description of only that portion of the database pertinent to a particular user’s needs, used to prevent sensitive data from being accessed by unauthorized personnel子 模式：只是与特定用户相关的那部分数据库的 一个描述。用来防止敏感数据被未授权的用户 获得
LOGO
Chapter 9: Database Systems 第九章： 第九章：数据库系统
9.1 Database Fundamentals 数据库基础 9.2 The Relational Model关系模型 9.3 Object-Oriented Databases面向对象数据库 9.4 Maintaining Database Integrity维护数据库的 完整性 9.5 Traditional File Structures传统的文件结构 9.6 Data Mining数据挖掘 9.7 Social Impact of Database Technology数据 库技术的社会影响
Can lead to redundant data能够导致冗长的数据 Deleting a tuple could also delete necessary but unrelated information删除一个元组也会删除了必要 的但不相关的信息
9-11
LOGO
Improving a Relational Design改进关系设计 改进关系设计 Decomposition: Dividing the columns of a relation into two or more relations, duplicating those columns necessary to maintain relationships分解：将一个关系的属性分解为 两个或多个关系，并且将必要的属性复制以维 持关系
9-8
LOGO
Relational Database Model关系数据库模型 关系数据库模型 Relation: A rectangular table关系：一个矩形 表格
Attribute: A column in the table属性：关系中的列 Tuple: A row in the table元组：关系中的行
9-7
LOGO
Database Models 数据库模型 Database model: A conceptual view of a database数据库模型：数据库的概念视图
Relational database model关系数据库模型 Object-oriented database model 面向对象数据库模 型
9-2
LOGO
Database 数据库 A collection of data that is multidimensional in the sense that internal links between its entries make the information accessible from a variety of perspectives 数据库是指一种多维的数据集合。 之所以说是多维的，是因为在这种集合中，通过 数据项间的内部链接，信息可以从不同的角度来 获取。
Each entity stored as a persistent object每个实体 是作为一个持久的对象存储的 Relationships indicated by links between objects通 过对象间的连接表明关系 DBMS maintains inter-object links数据库管理系统 主要处理内部对象间的连接
9-3
LOGO
Figure 9.1 A file versus a database organization 图9.1 文件与数据库结构的比较
9-4
LOGO
Figure 9.2 The conceptual layers of a database implementation 图9.2 一个数据库实现得概念性层次
9-20
LOGO
Figure 9.11 Another example of the JOIN operation图 图 9.11 JOIN运算的另外一个例子 运算的另外一个例子
9-21
LOGO
Figure 9.12 An application of the JOIN operation 图9.12 JOIN运算的应用 运算的应用
9-25
LOGO
Object-oriented Databases面向对象数据库 面向对象数据库 Object-oriented Database: A database constructed by applying the object-oriented paradigm 面向对象数据库：基于面向对象范型 的数据库
Matches design paradigm of object-oriented applications将面向对象应用的设计模范进行匹 配 Intelligence can be built into attribute handlers 将智能对象变为属性操作者 Can handle exotic data types能够处理不同类 型的数据
9-17
LOGO
Figure 9.8 The SELECT operation 图9.8 SELECT运算 运算
9-18
LOGO
Figure 9.9 The PROJECT operation 图9.9 PROJECT运算 运算
9-19
LOGO
Figure 9.10 The JOIN operation图9.10 JOIN运算 图 运算