Are subtypes that contain Nonunique subsets of the supertype entity set?Disjoint subtypes are subtypes that contain nonunique subsets of the supertype entity set.
Can a subtype have more than one supertype?A supertype can have one or more subtypes, and a subtype can have one or more supertypes. A supertype can be a subtype of some other supertype, and a subtype can be a supertype of some other subtype.
What is an overlapping subtype give an example?An example of an overlapping subtype structure would be the classification of employees at a College into instructors and administrators. Since some instructors are likely to be administrators, this would be an overlapping subtype structure. Hence, we would have EMPLOYEE as a supertype of INSTRUCTOR and ADMINISTRATOR.
How many Supertypes can a subtype be directly related to?However, a subtype is (directly) a subtype of only one supertype. Thus, the use of supertypes and subtypes in ERDs resembles the use of ``single inheritance'' between classes, in object-oriented programming.
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