Represent the Is A hierarchy, in the relational model. For each Is A relationship discuss your choice of the representation technique Discuss the circumstances in which an alternative representation (to the one you have chosen) would be better.

What will be an ideal response?

To represent the relationship IsA Employee, we would add an additional status attribute to the schema of Employee. This is because the entity types Secretary and Technician are likely to be disjoint. Similar considerations apply to IsA Student.

The downside of this representation is that some tuples will have null values over the attribute Specialization (in case of secretaries) and Major and Advisor (in case, say, of freshmen).

The relationship IsA Person is di?erent from the above two in that its subentities, Employee and Student, can have fairly large intersection. Thus, to avoid the duplication associated with the use of the Status attribute, we would use three relations, Person (SSN,Name,DOB), Employee (SSN,Department,Salary), and Student (SSN,GPA,StartDate).