MadeEasy Subject Test: Databases - Er Diagram

Question

Answer 1

Ans:3 Tables

Explanation:

Entity E1 is having key constraint and Total participation in relationship set R.

So we can merge E1 and R in to single relation which is as follows E1_R(A,B,C,D)    {A is Key}

Now E2 and E3 are having key constraint with relationship set R2.

so we can move R2 either on E2 side or E3 side.

If R2 is moved on E2 side then resulting tables are E2_R2(D,E,F,G)  and E3(G,H)

(or)

If R2 is moved on E3 side then resulting tables are E2(D,E,F) and E3_R2(G,H,D)

So minimum 3 tables are required.

Comments

Is it not possible to do this with 2 tables?

1. Merge E1 and R to get relation E1_R(A, B, C, D). A is the key here

2. Merge E1_R and E2 to get relation E1_R_E2(A, B, C, D, E, F). D is the key here

3. Merge R2 and E3 to get R2_E3(G, H, D). G is the key here.

So, we have 2 tables at the end

E1_R_E2(A, B, C, D, E, F) with D as its key and R2_E3(G, H, D) with G as its key.