ER Diagram- min no of relations

Question

How the correct answer is 2?

Answer 1

One Relation for E1
One Relation for E2R (since E2 has total participation, R can be merged with E2 with new key as composite key containing key from E2 and E1).

Eg.

E1: 

A (Key)	B
a1	b1
a2	b2
a3	b3

E2:

C (Key)	D
c1	d1
c2	d2
c3	d3

Relation R - 

Key of E1	Key of E2
a1	c1
a2	c1
a2	c2
a1	c3

Here E1 has partial participation as a3 does not participate in any relation. E2 has total participation because all c1, c2 and c3 participate in some relation.

So we can combine E2 and R as 

E2R - (CA is a composite key)

C	D	A
c1	d1	a1
c1	d1	a2
c2	d2	a2
c3	d3	a1

Hence 2 relations are required.

Comments

In your example, the primary key of E2 was 'C' initially.

But, when you tried to accommodate the relationship, you changed the primary key of E2 to (AC). Subsequently, information related to the original primary key was lost.

Answer 2

1 for E1,1 for E2 and both of them has M:N relation for this 1 table ....

overall 3 tables are required

Comments

you are wrong...2 tables are required

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You missed the total participation part(Double Line).  In case of total participation, relation can me merged with the totally participating entity.

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Don't you think the information that the information of primary key will be lost in that case.