Please Help

Question

Cardinality of $R_1$ and $R_2$ are $M$ and $1$, means it is $1:M$ relationship between $R_1$ and $R_2$ in R. So, It should be A.

Answer 1

See it is like this :

Many items of A are associated to one item of B..Or in other words for a given B we can have more than 1 A's but for a given A value we will only have one value of B atmost..

So with a given value of A we can determine B uniquely whereas converse is not true..

Hence in other words A is a key..

Hence B) is the correct answer..

Comments

So, you mean when it is said cardinalities of $R_1$ and $R_2$ are M and $1$, it means they are cardinalities in relationship, not individual. means it is $M:1$ relationship.