This document discusses the process of mapping an entity-relationship diagram (ERD) to a relational database schema. It outlines 7 steps: 1) creating relations for entity types, 2) handling weak entities, 3) mapping binary 1-to-1 relationships, 4) mapping binary 1-to-many relationships, 5) handling multi-valued attributes, 6) an example application of the steps, and 7) strategies for mapping specialization/generalization relationships between entity types. The document provides examples and diagrams to illustrate how each step in the mapping process transforms the ERD into a relational schema.

1. CS3200 – Database Design···Spring 2018···Derbinsky
ER-to-Relational
Mapping
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4. CS3200 – Database Design···Spring 2018···Derbinsky
Resulting Relational Schema
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5. CS3200 – Database Design···Spring 2018···Derbinsky
Example ERD
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6. CS3200 – Database Design···Spring 2018···Derbinsky
Step 1 Result
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7. CS3200 – Database Design···Spring 2018···Derbinsky
Step 2: Weak Entity Types
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i. For each weak entity type, create a
corresponding relation that includes all the
simple attributes
ii. Add as a foreign key all of the primary key
attribute(s) in the entity corresponding to
the owner entity type

8. CS3200 – Database Design···Spring 2018···DerbinskyExample
ERD
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9. CS3200 – Database Design···Spring 2018···Derbinsky
Step 2 Result
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10. CS3200 – Database Design···Spring 2018···DerbinskyStep 3: Mapping Binary 1 -to-1
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Foreign Key
i. Choose one relation as S, the other T
 Better if S has total participation (reduces
number of NULL values)
ii. Add to S all the simple attributes of the
relationship
iii. Add as a foreign key in S the primary key
attributes of T

11. CS3200 – Database Design···Spring 2018···DerbinskyExample ERD
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12. CS3200 – Database Design···Spring 2018···Derbinsky
Step 3 Result
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13. CS3200 – Database Design···Spring 2018···DerbinskyStep 4: Binary 1-
to-N
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i. Choose the S relation as the type at the
N-side of the relationship, other is T
ii. Add as a foreign key to S all of the
primary key attribute(s) of T
Another approach: create a relationship
relation

14. CS3200 – Database Design···Spring 2018···DerbinskyExample
ERD
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15. CS3200 – Database Design···Spring 2018···Derbinsky
Step 4 Result
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16. CS3200 – Database Design···Spring 2018···DerbinskyStep 5: Multivalued
Attributes
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i. Create a new relation S
ii. Add as foreign keys the primary keys of
the corresponding relation
iii. Add the attribute to S (if composite, the
simple attributes); the combination of all
attributes in S forms the primary key

17. CS3200 – Database Design···Spring 2018···DerbinskyExample
ERD
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18. CS3200 – Database Design···Spring 2018···Derbinsky
Step 6 Result
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19. CS3200 – Database Design···Spring 2018···Derbinsky
Step 7: Specialization/Generalization
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A. Multiple relations – subclass and superclass
 Usually works (assumes unique id at parent)
B. Multiple relations – subclass only
 Should only be used for disjoint
C. Single relation with one type attribute
 Only for disjoint, can result in many NULLs
D. Single relation with multiple type attributes
 Better for overlapping, could be disjoint

20. CS3200 – Database Design···Spring 2018···DerbinskySpecialization/Generalization
(A)
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21. CS3200 – Database Design···Spring 2018···DerbinskySpecialization/Generalization
(B)
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22. CS3200 – Database Design···Spring 2018···DerbinskySpecialization/Generalization
(C)
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23. CS3200 – Database Design···Spring 2018···DerbinskySpecialization/Generalization
(D)
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