involves only those employees who are salespersons; the Designs relationship involves
only those employees who are designers. It is usual to insist that the subtypes of a given
supertype are disjoint, in which case Fig. 13.3 could not model a situation in which an
employee could be both a salesperson and a designer.
Question
1.Which of the following restrictions do you think should apply to the use of the terms
entity subtype and entity supertype?
(a)an entity subtype must have the same identifier as its supertype;
(b)an entity subtype must have obligatory participation in its relationship with its
supertype;
(c)an entity subtype must have non-obligatory ...
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