Dimensional Modeling Roles Assignments

A table is determined to be a fact, dimension, or outrigger table, based on its dimensional modeling role. By default, a role is assigned to the table based on the relationships drawn to other tables. A table with no relationships is considered to be a dimension table. When you draw a relationship from one table to another, it is determined if the child table in the new relationship acts as a parent in any other relationship. Based on this information, the following rules are used to assign dimensional modeling roles:

• A fact role is assigned if the table has no parent relationships.
• A dimensional role is assigned if the table has no relationships to any table, if the table has a parent relationship to a fact table, or when the table has both parent and child relationships.
• An outrigger role is assigned if the table has a parent relationship to a dimensional table.

You can override a role assignment on a table-by-table basis in the Dimensional tab of the Tables editor.

More information:

Manually Assign Dimensional Modeling Roles