In data modeling, a subtype and its supertype share common attributes, and the relationships between the supertype and other entities can also be applied to the subtype. You can use this a rule to test two types of entities to see if they are subtype and supertype. If you try this with Personal Board and Team Board, you can see they are subtypes of Board. And if you test Team Creator with this rule, you can see it is not a subtype of User. Figure 5.19 shows the corrected data model of TaskAgile: