1 Entity-Relationship Modeling. 2 ER Graphical modeling technique Informal, understandable for...
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1 Entity-Relationship Modeling
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Transcript of 1 Entity-Relationship Modeling. 2 ER Graphical modeling technique Informal, understandable for...
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Entity-RelationshipModeling
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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
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Entities and attributes
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Relations (associations)
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Recursive relations
With roles
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Weak entities
ISA-hierarchy
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Cardinality & optionality
(0,n) (1,1)
optional mandatory
ERD -> relational schema
ERD -> relational schema
Solution 1E1 (K1, A1, …, Am, K2)E2 (K2, B1, …, Bn)
Solution 2E1 (K1, A1, …, Am)E2 (K2, B1, …, Bn, K1)
ERD -> relational schema
Solution 3E1 (K1, A1, …, Am, K2)E2 (K2, B1, …, Bn, K1)
ERD -> relational schema
Solution 4E1 (K1, A1, …, Am)E2 (K2, B1, …, Bn)R (K1, K2)