Figures 5.4, 5.7, and 5.39 each show the decomposition of a ternary relationship. Explain why the entity types SCHEDULE and PRESCRIPTION in Figures 5.4 and 5.7 are shown as base entity types, while the entity type USE in Figure 5.39 is shown as a weak entity type?

QUESTION:
Figures 5.4, 5.7, and 5.39 each show the decomposition of a ternary relationship. Explain why the entity types SCHEDULE and PRESCRIPTION in Figures 5.4 and 5.7 are shown as base entity types, while the entity type USE in Figure 5.39 is shown as a weak entity type?

 

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SOLUTION

SCHEDULE and PRESCRIPTION each possess unique identifiers, while USE has no partial key.

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