Subtype Relationships in the Logical Model

When you analyze the entities in your model, you may have some entities 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 an entity that defines the category and two or more additional entities that define each of the elements of the category. The parent entity of the category is considered the supertype and each child entity is considered a subtype.

You can create the following types of subtype relationships:

• Complete subtype relationship (in IDEF1X, when all categories are known).
• Incomplete subtype relationship (in IDEF1X, when all categories may not be known).
• Inclusive subtype relationship (in IE, when an attribute in the subtype entity can derive its value from one or more subtype entities).
• Exclusive subtype relationship (in IE, when an attribute in the subtype entity can derive its value from only one subtype entity).

You can also add a verb phrase for the subtype relationships in your model. You use a discriminator as the verb phrase for a subtype relationship.

By default, a supertype-subtype relationship between two different subtype entities belonging to same or different supertype group is not allowed. You can change this behavior using the Model Editor. For more information, refer to the Set Default Null Options, Data Types, Styles, and Object Owners topic. However, if you created a model in an older version of erwin Data Modeler (DM) and your model has such a supertype-subtype relationship, the relationship is preserved even when you open the model in the newer version of erwin DM.

More information:

Assign a Discriminator to a Subtype Relationship