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Entity-Relationship Modeling. ER. Graphical modeling technique Informal, understandable for laymen Coarse technique to design tables Provides rules of thumb for mapping to table structures. Entities and attributes. Relations (associations). Recursive relations. With roles. Weak entities.
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ER • Graphical modeling technique • Informal, understandable for laymen • Coarse technique to design tables • Provides rules of thumb for mapping to table structures
Recursive relations With roles
Cardinality & optionality (0,n) (1,1) optional mandatory
ERD -> relational schema Solution 1 E1 (K1, A1, …, Am, K2) E2 (K2, B1, …, Bn) Solution 2 E1 (K1, A1, …, Am) E2 (K2, B1, …, Bn, K1)
ERD -> relational schema Solution 3 E1 (K1, A1, …, Am, K2) E2 (K2, B1, …, Bn, K1)
ERD -> relational schema Solution 4 E1 (K1, A1, …, Am) E2 (K2, B1, …, Bn) R (K1, K2)