Conversion to Relational Model (Part 6)

Conversion to Relational Model

One-one-one relationship

a)

Converting the above ER diagram to a relational model:

A:                 B:                 C:                                  D:

a                   b                    c                          a | b | c

                                                                           

For the relationship D to be modeled as a relation, primary keys a, b, c from entities A, B and C respectively go to D as foreign keys which in turn are reset altogether as a primary key for the relation.

b) Alternative relational model for one-one-one relationship

 

Converting the above ER diagram to a relational model:

A:                 B:                 C:                                  D:

a                   b                    c                             did | a | b | c

Alternatively, if the relationship D has already a primary key did, it can be modeled as a relation by taking primary keys a, b, c from entities A, B and C respectively as foreign keys.

 Note: As with many-many binary relationship, with ternary relationships, the primary key of the relation modeled from the relationship needs to be determined after careful inspection.