Decomposition in DBMS 

 Decomposition kya hota hai?

Decomposition ka matlab hota hai ek badi table ko tod ke chhoti-chhoti tables mein divide karna, bina data ya information ko loss kiye.

Ye hum redundancy (duplicate data) ko kam karne ke liye karte hain, aur database ko clean aur structured banate hain.

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 Decomposition ki zarurat kyun padti hai?

Sochiye aapke paas ek aisi table hai:

 Table: StudentCourse

 Is table mein problems kya hain?

• Redundancy: Anjali aur Mr. Verma ka data repeat ho raha hai.

• Update Problem: Agar Mr. Verma ka naam badalna ho, toh har jagah change karna padega.

• Insert Problem: Jab tak student kisi course mein enroll nahi hota, aap course add nahi kar sakte.

• Delete Problem: Agar course ke saare students delete ho gaye, toh course info bhi chali jaayegi.

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 Decomposition ka Solution

Is table ko 3 alag tables mein divide kar dete hain:

 1. Student Table

 2. Course Table

 3. Enrollment Table

 Ab kya fayda mila?

• Data repeat nahi ho raha.

• Updates easy ho gaye.

• Har entity (Student, Course) alag table mein hai.

• Tables ke beech relation foreign key se maintain ho raha hai.

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 Achi Decomposition ke 2 Important Rules

1. Lossless-Join Decomposition

   • Jab aap chhoti tables ko dobara join karo, toh original table milni chahiye, bina data loss ke.

2. Dependency Preservation

   • Jo bhi functional dependencies pehle table mein thi, woh nayi tables mein bhi follow honi chahiye.

 Example: Project Table ko Decompose karna

 Original Table:

 Decomposition:

1. Project Table

2. Manager Table

Yeh dono tables ManagerID ke through linked hain. Redundancy khatam ho gayi aur data properly structured hai.

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 Summary Table