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tags:
Data Base
第七章: Entity-Relationship(ER) Model
Type of Attibutes
Entity
Entity Types and Key Attributes
Keys
Rekationships and Relationship Types
Relation 的 degree –- 有多少個 entity 參與 relation
Relationship Type 指的是 relation 的 datatype
Relationship Set 指的是 relation 的 instance
Recursive Relationship Type
Contraints on Relationship Types
Cardinality Ratio
Existence Dependarncy: 限定最小要多少 enitity 加入 relation
Participation constraint:
Attributes of Relationship Types
Relationships
定義: \(\{(e_1,e_2,...,e_n)|e_1 \in E_1,...,e_n \in E_n\}\)
where (e_1,e_2,… e_n) is relationship
ex: (JohnPharmacy) \(\in\) Works_in
Weak Entity Types
Summary of Notation for ER Diagrams
Alternative (min, max) Notation
UML Class Diagrams
Relation
Binary association:
Link attribute: 將 attribute 放入 box 中,用虛線連接
Multiplicities: min..max, 星號(*) 表示不限 participations
有兩種 relationships:
Other Alternative Diagrammatic Notations
Ternary Relationship