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You will find the Owns Destination checkbox in the Advanced properties panel of the relationship.
Now that you have your to-one relationship, you can use it to flatten the appropriate attributes and relationships into your subentity. To do that, turn down the arrow beside the to-one relationship, select the attribute or relationship you would like flattened and then click the flatten button on your toolbar. You will need to rename your flattened property so that it matches the property name of the parent's property.
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