entity-relationship modeling
Post on 05-Jan-2016
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DESCRIPTION
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. - PowerPoint PPT Presentation
TRANSCRIPT
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)
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