1. Conversion from ER diagram to relational model
ER is a visual model
The relational model is a matemathical model
Conversion from ER diagram to relational model

2. Database development as part of systems development
Analysis phase
Draw an ER-diagram
Design phase
Convert ER-diagram to relational model.
Check if the relations are sufficiently normalized.
Realization phase
Create tables in a DBMS.
Conversion from ER diagram to relational model

3. Procedure for conversion from ER to relational model
Strong entity types
have their own relation with all the single-valued attributes.
composite attributes: Simple attributes (“leaves”) in the relations.
primary key transferred from ER to the relation.
Conversion from ER diagram to relational model

4. Converting weak entities
Weak entity types
have their own relation with all single-valued attributes
partial key transferred from ER to the relation
foreign key to referring to the “strong” entity (identifying relationship).
primary key = partial key + foreign key to “strong” entity.
Conversion from ER diagram to relational model

5. Binary relationships 1:1
Binary 1:1 relationships (rare)
data from the relationship (if any) integrated into one of the related entities [your choice].
one of the related relations gets a foreign key to the other [your choice: easy to find a “way” from on to the other, but not vice versa]
1:1 relations are rare in ER-diagrams {they are usually modeled as a single entity }
Conversion from ER diagram to relational model

6. Binary relationships 1:N
Binary relationships with cardinality 1:N
data from the relationship (if any) integrated into the relation with the “N”
The “N” relation has a foreign key to the “1” relation.
Conversion from ER diagram to relational model

7. Binary relationships N:M
Binary relationships with cardinality N:M
Own relation with 2 foreign keys (1 for each of the relation entities)
Date (like timestamps, etc.) on the relationships goes into the relation.
Conversion from ER diagram to relational model

8. Multi valued attributes
Own relation
Foreign key to the “owning” relation.
Conversion from ER diagram to relational model

9. Conversion from ER diagram to relational model
N-ary relationships
Relationships with N (more than 2) entities
Own relation with N foreign keys (1 for each related entity)
Conversion from ER diagram to relational model

10. Conversion from ER diagram to relational model
Inheritance, page 295
ER-modeling allows inheritance between entity types.
Problem
No inheritance in the relational model.
Solution
Try to avoid inheritance in ER.
Conversion from ER diagram to relational model