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Unification is the merging of two or more foreign keys with the same name into a single foreign key based on the assumption that the foreign keys must be identical. Unification occurs because normalization rules prohibit the existence of two attributes or columns with the same name in a single entity or table.
When you create multiple relationships between a parent and child entity, the child entity inherits multiple instances of the same foreign key. By default, only one occurrence of the foreign key in the child entity is unified and displayed.
If you want to display both instances of the foreign key, because you want to preserve them differently in your model, you must assign a rolename to the second instance of the foreign key.
Note: By default, a column in the physical model inherits its name from the corresponding attribute in the logical model. For this reason, only the logical model is checked to determine if a duplicate attribute exists in an entity. Unless you manually change the corresponding column name in the physical model, the migrating key option that you choose for the logical model automatically applies to the physical model.
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