Multivalued Dependency (MVD) in DBMS 

 Definition:

Multivalued Dependency tab hoti hai jab ek column (attribute) kisi doosre column ke multiple values ko independently decide karta hai.

Iska matlab:
Ek hi key ke liye, do alag-alag attributes ke multiple values ho sakte hain, jo ek doosre se independent ho — lekin dono same key pe depend karte hain.

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 Multivalued Dependency kyun important hai?

• Ye data mein duplicate/redundant rows create kar sakti hai.

• Data ko samajhne aur update karne mein problem hoti hai.

• Isko fix karne ke liye hum 4NF (Fourth Normal Form) ka use karte hain.

 Example:

Ek table lete hain:

Yahaan par:

• Student 101 ke 2 hobbies hain: Painting aur Music

• Student 101 2 languages jaanta hai: English aur French

• Hobby aur Language ka aapas mein koi lena dena nahi hai, lekin dono Student_ID pe depend karte hain.

 Multivalued Dependency yahaan kya hai?

Ye isliye MVD hai kyunki:

• Hobby aur Language independent hain.

• Lekin dono ek hi Student_ID pe depend karte hain.

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 MVD se kya dikkat hoti hai?

1. Redundancy – same data baar-baar aata hai.

2. Update Problem – agar ek hobby ya language update karni ho to kai rows change karni padti hain.

3. Wastage of Storage – unnecessary rows store hoti hain.

 Solution – 4NF Normalization

Is problem ko solve karne ke liye, hum table ko 2 parts mein todte hain:

 Hobby Table:

 Language Table:

Ab dono independent attributes alag ho gaye — aur duplication bhi nahi hai!

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 Summary Table: