Working with Data Models › Working with Transformations › Using a Transformation to Roll Down a Subtype Relationship

Using a Transformation to Roll Down a Subtype Relationship

A subtype relationship is a relationship between a supertype entity and a subtype entity. You can use a subtype relationship to create a hierarchical grouping of entities that share common characteristics.

When you transition from one design layer to another, or when you change a model over time, the way that you represent subtype relationships can change. You can apply a transformation to roll down a supertype entity to the subtype entities.

The main reasons why you apply a transformation to roll down a subtype relationship include:

• You want to simplify a model.
• The subtype relationship is not appropriate for the current design layer.
• You want to improve query performance.

Supertype Subtype Roll-Down Wizard

To roll down a subtype relationship, you select the subtype relationship symbol , and then click the Supertype-Subtype RollDown icon on the Transformations toolbar.

Result of Rolling Down a Subtype Relationship

When you click Supertype-Subtype RollDown to roll down a subtype relationship, you:

• Create a subtype entity that corresponds to each source subtype entity. The new subtype entity contains all primary key and non-key attributes from the source subtype entity and any migrated foreign key and non-key attributes from the source supertype entity. When you create attributes in the subtype entity, you preserve the attribute order in the source supertype entity, and then the attribute order in the source subtype entity. The primary key of the subtype entity is the primary key of the source subtype entity. The subtype entity appears in the Model Explorer under the Entities folder.
• If the source supertype entity that you roll down contains a foreign key (FK) that does not migrate to the subtype entity, you create a corresponding foreign key attribute in the target subtype entity. The foreign key in the new subtype entity inherits object properties from the corresponding foreign key in the source entities.
• If the source supertype or subtype entity that you roll down contains attributes that you unified, you unify the corresponding attributes in the new subtype entity.
• Creates all relationships associated with the source supertype and subtype entities that you roll down, and preserves all migrated keys.
• Preserves all object properties for the supertype and subtype entities that you roll down.

Important! Once you apply the Supertype Subtype Roll-Down transformation, it cannot be reversed. While in the current modeling session however, you can undo the action.

More information:

Roll Down a Subtype Relationship with a Transformation