Self Doubt

Question

How many minimum number of tables required to represent a Department entity  which having two multi valued attributes phone and office?

Comments

are you having only two attributes or any other attribute is present other than multivalued?

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Yes there are some more attributes are present

Answer 1

There will be total 3 three tables, because each MV needs separate table which contains PK + MVA.

Basic rule is to uniquely identify/ select any attribute when requested from database. If we put MVA into single table like

person_ID	fav_colors	age
person_1	Red, Blue	20
R2D2	Black	22

In the above table, fav_colors are the multivalued attributes.The problem with doing it is that it is now difficult (but possible) to search the table for any particular fav_color that a person might have. 

Multivalued attributes need a separate table so in my example we have only one Multivalued attribute(fav_colors).

Colors

person_ID	fav_colors
person_1	Red
person_1	Blue
R2D2	Black

 

So, in your case it will be T1(dept_ID, A, B, C), T2(dept_ID, phone), T3(dept_ID, office)

Total 3 tables.  

Answer 2

Since there are some more attributes other than multivalued attributes, 2 tables are required.

First table will contain the primary key and the attributes other than multivalued attributes and the second table will contain the primary key and multivalued attributes.

Comments

Each MVA needs separate table....Table 2 will be further gets split into (Dno,Phone) and (Dno, office)

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total 3 tables