Entity relationship modeling
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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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Entity-Relationship Modeling

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Entity-RelationshipModeling


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


ISA-hierarchy


Cardinality & optionality

(0,n) (1,1)

optional mandatory


ERD -> relational schema


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)


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