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tags:
Data Base
第八章: Enhanced Entity-Relationship(EER) Model
Representing Specialization in EER Diagrans
Constraints on Specialization and Geralization
Predicate-defined(condition-defined) subclass
Attribute-defined Constraints
User-defined Constraints
有兩種 constraints 可以應用於 specialization 與 generalization :
Hierarchies and Lattices
Formal Definitions of EER
Specialization Z: Z = \(\{S_1,S_2,...,S_n\}\) 是一個有同樣 superclass G 的 subclasses set
G 叫做 subclasses 的 generalization
Z \(\in\) Total if \(S_1 \cup S_2 \cup S_3 \cup ... \cup S_n = G\), otherwise, Z is partial
Z \(\in\) disjoint if \(S_i \cap S_j\ for\ i \ne j\) otherwise, Z is overlapping
Predicate defined: 符合條件 P 在 C 的 attributes S, 以 S = C[p] 表示
Attribute-defined specialization: if predicate A = ci, 則屬於某個 subclass
非 predicate defined 者為 user-defined
Category: 一個 subset T \(\subset\) (\(D_1 \cup D_2 \cup ... \cup D_n\)), D 為不同 superclass
Design Issues