第一章
关系数据库基础知识(续)
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1.3 数据库设计
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1.3.1 数据建模
用来解释数据库处理系统的需求，并使之文档化，
为显示用户需求的全局结构提供了框架，对自顶向
下设计特别有用。
Semantic model
extended model managed to capture all of the
semantics of the situation under consideration
Entity-relationship approach
most commonly used in practice
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1.3.1 数据建模
For a binary relationship set the mapping
cardinality must be one of the following types:
One to one
One to many
Many to one
Many to many
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1.3.1 数据建模
One to one
One to many
