edited by
27,601 views
43 votes
43 votes

In an Entity-Relationship (ER) model, suppose $R$ is a many-to-one relationship from entity set E1 to entity set E2. Assume that E1 and E2 participate totally in $R$ and that the cardinality of E1 is greater than the cardinality of E2.

Which one of the following is true about $R$?

  1. Every entity in E1 is associated with exactly one entity in E2
  2. Some entity in E1 is associated with more than one entity in E2
  3. Every entity in E2 is associated with exactly one entity in E1
  4. Every entity in E2 is associated with at most one entity in E1
edited by

5 Answers

Best answer
54 votes
54 votes

Since it is a many to one relationship from E1 to E2, therefore:

  1. No entity in $E1$ can be related to more than one entity in $E2$. ( hence B is incorrect)
  2. An entity in $E2$ can be related to more than one entity in $E1$.(hence C and D are incorrect).

Option (A) is correct: Every entity in E1 is associated with exactly one entity in E2.

edited by
45 votes
45 votes

It is given that  "R is a many-to-one relationship from entity set E1 to entity set E2"

E1------N-------R---------1-------E2

Therefore,

Participation of E1:=1

Cardinality of E1:=1

 

Participation of E2:=1

Cardinality of E2:=N

 Therefore, Answer is (A): Every entity in E1 is associated with exactly one entity in E2 because the number of relationships in which an entity of a entity type E1 can participate is equal to 1.


 Note: "Cardinality of a set/Entity set" is a different thing and "Cardinality of an Entity in a relationship" is a different thing.

Cardinality of a set/Entity set: Number of instances/elements in that set.

Cardinality of an Entity in a relationship: Maximum number of relationships in which an entity of a given entity type can participate.

Therefore, the line "cardinality of E1 is greater than the cardinality of E2" just means that the number of instances/entities in E1 is more than the number of instances/entities in E2

edited by
12 votes
12 votes
Since total participation of both side And many- one is given then E1 must be merge with Relation.

So Every entity of E1 must be associated with exactly one entity in E2

A is answer
10 votes
10 votes

Total participation means every entity is involved in relation.It is denoted by double lines.

Many to one relationship from Entity set E1 to Entity set E2 means no entity in E1 can be related to more than one entity of E2 but one entity of E2 can be related to more than one entity of E1. 

So,right answer is option A.

edited by
Answer:

Related questions

32 votes
32 votes
6 answers
4