➢Hierarchical Model ➢Network Model ➢Relational Model
➢Main factors of the data model
➢Data structure ➢Data operation ➢Integrity constraints
精选ppt
7
数据模型的组成要素
精选ppt
9
概念模型基本概念
实体（Entities)
客观存在并可相互区别的事物，可具体，可抽象
• 例：职工、学生、系
属性（Attribute）
实体具有的某一特性
• 例：学生实体有学号、姓名、性别、出生年份等属性
码（Key）
唯一标识实体的属性集
• 例如 学号是学生实体的码
域 （Domain）
某属性的取值范围
Entity set = rectangle. Attribute = oval, with a line to the rectangle representing its entity set.
精选ppt
13
Example
name
address
Stars
Entity set Stars has two attributes, name and address.
supported by some DBMS.
The concept model is a middle layer between the real world and the machine world.
客观对象
概念模型
数据模型
现实世界
信息世界
精选ppt
机器世界
5
The classification of the models
Two steps of the abstraction and modeling: 1. The objective objects in the real world is
abstracted to a concept model. 2. Concept model is converted to a data model that
一对一联系(1:1)
一对多联系(1:n)
多对一联系(n:1)
多对多联系(m:n)
精选ppt
11
Entity Sets
Entity = “thing” or object. Entity set = collection of similar entities.
Similar to a class in object-oriented languages.
实体集（Entity Set）同ຫໍສະໝຸດ 实体的集合• 如 全体学生
精选ppt
10
概念模型的基本概念
实体间的联系（Relationship）
现实世界中事物内部以及事物之间的联系在信息世 界中反映为实体内部的联系和实体之间的联系
• 例 张山选修数据库课程。
• 学生实体和课程之间通过选修联系
两个实体之间的联系：
精选ppt
8
E-R Model
The concept model is represented by Entity-Relationship（E-R）diagrams. The E/R model
Describes kinds of data and how they connected. Can be converted to relational model later.
Attribute = property of (the entities of) an entity set.
Attributes are simple values, e.g. integers or character strings.
精选ppt
12
E/R Diagrams
In an entity-relationship diagram:
精选ppt
3
Data Model should :
Simulate the real world comparatively truly Be easy to understand Be easy to be implemented by computer
精选ppt
4
Abstraction and Modeling
Database Principles
精选ppt
1
Chapter 2 Database Modeling
Data Models Concept Model & Data Model Entity-Relationship diagrams
精选ppt
2
What are Data Model?
Computer simulation of the real world. To abstract, denote and transact the information in the real world.
communicate with each other. ➢ It should be simple, clear and easy to understand by
users.
精选ppt
6
Data model
➢Modeling data from the viewpoint of computer. ➢Mainly used for a DBMS realization. ➢Traditional data models
Concept model
➢ Also called information model. ➢ Modeling data from the viewpoint of users. ➢ a middle layer between the real world and the machine
world. ➢ Mainly used for a database design. ➢ The language in which the database designers and users
数据结构
指所研究数据集合及数据间的联系 是对系统静态特性的描述
数据操作
对数据库中各类数据允许执行的操作及有关的操作规则
• 检索、更新（包括插入、删除、修改）
是对系统动态特性的描述
数据的约束条件
一组数据及其联系所具有的制约规则，用以限定符合数 据模型的数据库状态以及状态的变化，以保证数据的正 确、有效、相容