ER Model to Relational Model Conversion

Question

What is the minimum number of relations required to represent a one-to-many relationship having total participation on the many side?

Can i have just a single table with all attributes and (A1,B1) as a composite primary key?

Comments

@priyanshu710

 

1. https://gateoverflow.in/218954/what-an-interesting-dbms-question 

 

2. https://gateoverflow.in/217336/er-diagram-to-relation-doubt

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I think it's answer will be 2

Answer 1

Yes, but only if there is total participation on 1-side too. If many-side is totally participating and 1- side is partially participating, then your composite primary key (A1, B1) will have NULL values in B1 field for some of the entries and violate the condition of primary key’s prime attributes not being NULL. Hence, we require 2 tables to represent the ER model if there’s partial participation on 1-side and total participation on many-side.

On the other hand, if both sides are totally participating, then a single table with (A1, B1) as the primary key will do.

Answer 2

Here you can get away with just 2 tables. One table will be E1 & R having B1/B2 as foreign key and A1/A2 as primary key , and the other table will have just E2.