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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ER

  • Graphical modeling technique

  • Informal, understandable for laymen

  • Coarse technique to design tables

  • Provides rules of thumb for mapping to table structures







Cardinality optionality
Cardinality & optionality

(0,n) (1,1)

optional mandatory



Erd relational schema1
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 schema2
ERD -> relational schema

Solution 3

E1 (K1, A1, …, Am, K2)

E2 (K2, B1, …, Bn, K1)


Erd relational schema3
ERD -> relational schema

Solution 4

E1 (K1, A1, …, Am)

E2 (K2, B1, …, Bn)

R (K1, K2)


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