Relationships and Domains › Relationships in the Physical Model › Subtype Relationships in the Physical Model

Subtype Relationships in the Physical Model

When you analyze the tables in your model, you may have some tables that define an entire type, or classification of a particular item. In a data model, you can show that full time and part time employees are part of a larger category, EMPLOYEE, by creating a subtype relationship. A subtype relationship connects a table that defines the category and two or more additional tables that define each of the elements of the category. The parent table of the category is considered the supertype and each child table is considered a subtype.

When you add a subtype relationship in the logical model and then transform the logical model or forward engineer a logical/physical model, you can specify how to model the subtype relationship. You can model subtype relationships in any of the following ways:

As Is

Leaves the subtype relationship symbol in the diagram window as an indication to the physical modelers that the relationship needs to be resolved.

Roll down

Creates two tables based on a combination of the supertype and the subtype entities.

Roll up

Creates one table that includes all the attributes from the initial three entities.

Identity

Adds three tables based on the initial entities and the tables joined with identifying relationships.