EER Diagram - Mixing Specialization and Disjointness Constraints Among Subtypes
I'm trying to design an EER diagram that has the supertype Student with the following subtypes: Undergraduate, Graduate, and Research Assistant. A Student must be either an Undergraduate or a Graduate, and a Student may or may not be a Research Assistant.
I'm not entirely sure how to depict these relationships. Should I have supertype/subtype relationships going from Student to subtypes Undergraduate and Graduate with total specialization and disjointness while a separate relationship goes to Research Assistant with only partial specialization?
Or should I have relationships that have total specialization and overlapping and define the subtype discriminator to reflect the constraints above?
Sorry if I'm missing something obvious.
Your first diagram is correct and clearly depicts the specialization you described.
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