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How do I model a ternary relationship in Database Design Studio?
As a deliberate choice, Database Design Studio does not have a ternary
relationship type. This is because we believe that a ternary relationship can be
better modeled using a Weak Entity as we discuss below.
As an example consider this scenario:
The relationship “attendance” is a ternary relationship between the three entities, and clearly must be a
table, with its primary key made up of the primary keys from the 3 entities to
which it is related.
If you make “attendance” a weak entity, with Weak Relationship to all of the three other entities you will achieve the desired end result of
a "ternary" type of relationship, as shown in the ERD below:
The Data Structure Diagram using the rules of the ERD is shown below:
As you can see, Database Design Studio can model a ternary relationship by
breaking it down to binary relationships and using a weak entity and Weak Relationships.