4 Entity Supertypes and Subtypes u Generalization hierarchy –Depicts a relationship between a higher-level supertype entity and a lower-level subtype entity u Supertype entity –Contains shared attributes u Subtype entity –Contains unique attributes
13 Disjoint Subtypes u Also known as non-overlapping subtypes –Subtypes that contain a subset of the supertype entity set –Each entity instance (row) of the supertype can appear in only one of the disjoint subtypes u Supertype and its subtype(s) maintain a 1:1 relationship u Such disjoint relationships are indicated by symbol “G” or wording “or”
15 A Generalization Hierarchy : Disjoint subtype
16 A Generalization Hierarchy : Overlapping Subtypes
17 Overlapping Subtypes or NonDisjoint Subtypes u Also known as non-overlapping subtypes –Subtypes that contain a subset of the supertype entity set –Each entity instance (row) of the supertype can appear in one or more of the nondisjoint subtypes u Such nondisjoint or overlapping relationships are indicated by symbol “Gs” or wording “And”
18 A Generalization Hierarchy with Overlapping Subtypes and Disjoint Subtypes
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