An ER model of a database consists of entity types A and B. These are…
2021
An ER model of a database consists of entity types A and B. These are connected by a relationship R which does not have its own attribute. Under which one of the following conditions can the relational table for R be merged with that of A?
- A.
Relationship R is one-to-many and the participation of A in R is total
- B.
Relationship R is one-to-many and the participation of A in R is partial
- C.
Relationship R is many-to-one and the participation of A in R is total
- D.
Relationship R is many-to-one and the participation of A in R is partial
- E.
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Correct answer: C
To merge relationship R with entity table A, table A must be able to store the foreign key of the related B entity.
If R is many-to-one from A to B, then many A records can be associated with one B record. So the primary key of B can be stored as a foreign key in table A, and a separate table for R is not needed because R has no attributes of its own.
Total participation of A is required because every A entity must participate in R. Therefore the foreign key in A will always have a value.
Option D is not correct because it says the participation of A is partial. In partial participation, some A entities may not participate in R, so the foreign key in A may be NULL. Hence this is not the best condition for safely merging R with A.
Therefore, the correct answer is Option C: Relationship R is many-to-one and the participation of A in R is total.