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# Entity-Relationship Modeling PowerPoint PPT Presentation

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.

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

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)