1

Entity-RelationshipModeling

2

ER

• Graphical modeling technique

• Informal, understandable for laymen

• Coarse technique to design tables

• Provides rules of thumb for mapping to

table structures

3

Entities and attributes

4

Relations (associations)

5

Recursive relations

With roles

6

Weak entities

ISA-hierarchy

8

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)