ER Diagram

Question

Consider the following $ER$ model: 

If $‘n’$ entries in $E_1$ and $‘m’$ entries in $E_2$. How many entries in relationship set $(R)$?

• A. At least $n$
• B. At most $n$
• C. Exactly $n$
• D. At least $n$ and atmost $m$

Answer 1

There are some Conventions that Arrow ( $\rightarrow$) Mark represents $One$ and Straight line ( $-$) represents $Many$, Hence here One to One Relationship.

And Single line represents Partial Participation and Double line represents Total Participation.. Hence here, $E1$ is having Total Participation in the Relationship $R$ and $E2$ is having Partial relationship in $R$.

Now, Because of Total Participation of $E1$, $R$ has to contain at least $n$ rows. But Because of One to One relationship, We can't have more than $n$ rows in $R$ (Try it and see)

Hence answer would be Option $C$ But with added condition that $m > n$

Comments

n>m condition is automatically eliminated as the relationship is one-to-one and there is a total participation.So the relationship between n and m will be

n<=m.

So the answer will be exactly n.

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Total participation is on one side only.

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If the cardinality is 1:m then the answer would be At least n right?