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)