When you create a non-identifying relationship, you must decide whether or not the foreign key attributes in the child entity or table that are inherited from the parent can have a Nulls Allowed or No Nulls value. A Nulls Allowed value means that the child entity or table can exist without the existence of the parent and the relationship is optional. A No Nulls value means that the child entity or table is dependent upon the parent entity or table for its existence and the relationship is mandatory.
You can set default relationship null options in the Model Editor in the Defaults tab. However, you may find that you want to override this default setting. You can do this by changing the setting in the Relationships editor.
You can optionally display Null or Not Null values for each column in a table. If you want to see Null or Not Null in the model, set the Null Display option.
Note: Identifying relationships cannot be Null because the foreign key appears as a part of the primary key in the child entity or table.
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