GATE CS 2017 Set 2 — Question 17
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Databases → ER Model → ER to Relational Mapping
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Question
An ER model of a database consists of entity types A and B. These are connected by a relationship R which does not have its own attribute. Under which one of the following conditions, can the relational table for R be merged with that of A?
Correct answer
(C) Relationship R is many-to-one and the participation of A in R is total.
Solution
To merge the relationship table with the entity table , two conditions must be met:
1.Cardinality Constraint: Every entity in must be associated with at most one entity in . This means the relationship from to must be many-to-one (or one-to-one). In a many-to-one relationship from to , is on the 'many' side, meaning each relates to exactly one .
2.Participation Constraint: To avoid null values in the foreign key column (which stores the primary key of in table ), every entity in must participate in the relationship. This is called total participation.
Thus, if is many-to-one from to and has total participation in , the relationship can be represented by adding 's primary key as a foreign key in 's table without needing a separate table for .Therefore, the correct option is (C).Continue learning with Success Tracker
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