1. 1 ER Modeling BUAD/American University Mapping ER modeling to Relationships

2. 2 ER Modeling BUAD/American University Review of Relation Properties Relation –Every relation has a unique name. –Every attribute value is atomic. –Every row is unique. –Attributes in tables have unique names. –The order of the columns is irrelevant. –The order of the rows is irrelevant.

3. 3 ER Modeling BUAD/American University Review of Relational Keys and Structures Primary Key Candidate Key Composite Key Foreign Key: an attribute (or a composite attribute) in a relation that serves as the primary key of another relation –One-to-Many Relationship –Many-to-Many Relationship

4. 4 ER Modeling BUAD/American University Schema for four relations (Pine Valley Furniture)

5. 5 ER Modeling BUAD/American University Review of Integrity Constraints Domain Constraints –Allowable values for an attribute. Entity Integrity –No primary key attribute may be null. Referential Integrity: maintains consistency among related relations –Foreign Key value in one relation must match a primary key value in other relation –For example: Delete Rules Restrict, Cascade, Set-to-Null Operational Constraints: Business rules

6. 6 ER Modeling BUAD/American University Referential integrity constraints (Pine Valley Furniture)

7. 7 ER Modeling BUAD/American University Well-Structured Relations Is a relation that contains minimal redundancy and allows users to insert, modify, and delete the rows in a table without errors or inconsistencies

8. 8 ER Modeling BUAD/American University Transforming E-R Diagrams Into Relations 3. Map Binary Relationships –One-to-Many - Primary key on the one side becomes a foreign key on the many side –Many-to-Many - Create a new relation with the primary keys of the two entities as its primary key –One-to-One - Primary key on the mandatory side becomes a foreign key on the optional side

9. 9 ER Modeling BUAD/American University Translating an ER diagram into Relationships (one to many) Create one table for each entity For each entity that is only at the “one” side a one to many relationship (not many end), create a single column primary (use an arbitrary unique number if no natural key exists) For each entity that is at the many side of a one to many relationship, use the primary key of the parent (one side) in the table as the foreign key Entity at the many side of one or more relationship has a natural key, use that single column as the primary key. Else, concatenate the primary key of the one side with any columns needed for uniqueness

10. 10 ER Modeling BUAD/American University Example of mapping a 1:M relationship (a) Relationship between customers and orders (0, M) 1

11. 11 ER Modeling BUAD/American University (b) Mapping the relationship

12. 12 ER Modeling BUAD/American University Example of mapping an M:N relationship (a) Requests relationship (M:N) (0, M)(1, M)

13. 13 ER Modeling BUAD/American University (b) Three resulting relations

14. 14 ER Modeling BUAD/American University Mapping a binary 1:1 relationship (a) Binary 1:1 relationship (0, 1) 1

15. 15 ER Modeling BUAD/American University (b) Resulting relations

16. 16 ER Modeling BUAD/American University Transforming E-R Diagrams Into Relations 4. Map Associative Entities –Primary Keys Default primary key for the association relation is the primary keys of the two entities

17. 17 ER Modeling BUAD/American University Mapping an associative entity with an identifier (a) Associative entity (SHIPMENT)

18. 18 ER Modeling BUAD/American University (b) Three relations

19. 19 ER Modeling BUAD/American University Mapping Supertype/subtype relationships to relations

20. 20 ER Modeling BUAD/American University Map Composite and Multi-valued Entities to Relations –Composite attributes: Use only their simple, component attributes –Multi-valued Attribute - Becomes a separate relation with a foreign key taken from the superior entity

21. 21 ER Modeling BUAD/American University (a) CUSTOMER entity type with composite attribute Mapping a composite attribute