GATE CS 2015 Set 1 — Question 48
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Databases → ER Model → 1NF, 2NF, 3NF
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Question
Consider an Entity-Relationship (ER) model in which entity sets and are connected by an relationship . and are connected by a (1 on the side of and on the side of ) relationship . has two single-valued attributes and of which is the key attribute. has two single-valued attributes and of which is the key attribute. has two single-valued attributes and of which is the key attribute. The relationships do not have any attributes.If a relational model is derived from the above ER model, then the minimum number of relations that would be generated if all the relations are in 3NF is ___________.
Correct answer
4 to 4
Solution
The mapping from ER to Relational model is as follows:
1.Entity becomes a relation .
2.Entity becomes a relation .
3.Entity becomes a relation .
4.Relationship is , so it requires a separate relation .
5.Relationship is ( is 1-side, is n-side). This is mapped by adding the primary key of the 1-side () as a foreign key to the relation for the n-side (). So becomes . No separate table is needed for .
Total relations generated: . The count is 4.Continue learning with Success Tracker
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