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+4 votes
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How many minimum relations required for given ER diagram ?

 

asked in Databases by Active (1.2k points) 6 14 | 191 views
5 tables

for every entity require 5 tables and for relation r6 it there is weak entity but it indicated with m:n relation in figure so 5 tables required
I am getting 8 as an answer. 5 for each entity set and 3 different tables for the relationships R1, R2 and R5 since they are many-to-many relationships. Please correct me if i am wronge.
When a relation is in 1-1 form there is no need to create a table. Only for M:N relations we construct seperate tables so no need to constuct tables for 1-1 relations.
but we have to maintain foreign key constraints here.

2 Answers

+1 vote
5 for each entity set and 3 different tables for the relationships R1, R2 and R5 since they are many-to-many relationships.Thus, total 8.
answered by (201 points) 3 12
R5 is a 1 to 1 relationship  given in diagram

E1(A,B,C)

R1(A,D)

E2(D,E)

R2(D,D')

E4R5(K,L,F)

E3(F,G)

E5(H,I,J,F)

R3(D,F)

NOTE: We can not merge $E_{1}R_{4}E_{4}$ Bcz in $R_{1}(A,D))$ $A$ have to refers to "PK" of $E1$ and if we merge  $E_{1}R_{4}E_{4}$ then ${A,K}$  will be PK of this table not just $A$

 

+1 vote

Total 8 tables are required

Let (EntityName,NumberOf Table)

(E1,1),(E2,3),(E3,1),(E4,1),(E5,2) 

E2 has 3 tables because in suppose we have 

Recursive Relationship -types of relationships in er diagram

So 3 tables required for E2 and E5 is weak entity so 2 tables required

weak entity type(entity and its types)

total = 1+3+1+1+2 = 8 tables 

Reference :-http://www.edugrabs.com/entity-and-its-types/

answered by Boss (5.9k points) 2 6 15


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