SSD7-1.2课件.pptVIP

Wei Lu 1.2 Relational Databases Tianqing Zhang School of Computer (School of Software) zhangtq@scu.edu.cn 1.2.1 Key Concepts Data Model Relational Data Structure Properties of Tables Keys Relation Integrity Background The relational Database Management System (RDBMS) has become the dominant data-processing software in use today. Brief history of the Relational Model E.F.Codd “A Relational Model of Data for Large Shared Data Banks” 大型共享数据库数据的关系模型 IBM RDBMS System R 第一个商品DBMS IBM DB2, Oracle, Sybase, Ingres, MS SQL Server… 1.2.1 Key Concepts Data Model An integrated collection of concepts for describing and manipulating data, relationships between data, and constraints on data in an organization. A data model can be thought of as comprising three components: 数据模型三要素 Data structure 数据结构 Data manipulation 数据操纵 Constraints of data integrity 数据的完整性约束 Key Concepts The Relational Model (Codd 1976) is currently the most popular model for database systems. The simplest and most uniform data structure: data are stored in tables 最简单 最统一 二维表 The most formal of all data models. It is based on the mathematical concept of a relation in set theory: a table is a relation 集合论为理论基础 Example：the MEMBER table Member Relational Data Structure 1 Relation 关系 A relation is a table with columns and rows. 二维表 Attribute (columns, field) 属性（列，字段） An attribute is a named column of a relation. Domain 域 A domain is the set of allowable values for one or more attributes. Tuple (row, record) 元组（行，记录） A tuple is a row of relation. Relational Data Structure 2 Intension 内涵 关系的结构以及域、取值限制 The structure of a relation, together with a specification of the domains and any other restrictions on possible values Extension 外延 元组 The tuples are called extension (or state) Degree (arity) 目，度 The degree of a relation is the number of attributes it contains. Cardinality 基数 The cardinality of a relation is the number of tuples it contains. Relational Data Structure 3 Relational database 关系数据库 A col