Question

If one instance of ENTITY B must be related to one and only one instance of ENTITY A, and one instance of ENTITY A may be related to many instances of ENTITY B, which of the following should be written on the end of the relationship line next to ENTITY B in the figure above?

1) 1
2) N
3) M
4) A

Answer 1

In a "one-to-many" relationship between ENTITY A and ENTITY B, the relationship line next to ENTITY B should be annotated with the number 1 to indicate that each instance of ENTITY B is related to exactly one instance of ENTITY A.

Step-by-step explanation:

If one instance of ENTITY B must be related to one and only one instance of ENTITY A, and one instance of ENTITY A may be related to many instances of ENTITY B, this is a classic example of a "one-to-many" relationship in the context of entity-relationship diagrams (ERDs) which are often used in database design. In such a diagram, the relationship line between ENTITY A and ENTITY B would be annotated to reflect this cardinality. On the ENTITY B side, which has a strict one-to-one relation, it should be annotated with the number 1 to indicate that each instance of ENTITY B is related to exactly one instance of ENTITY A. Conversely, the ENTITY A side should reflect the "many" part of the relationship, which is commonly denoted by the letter N or the symbol M.