Schemas in DBMS

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 Schema kya hota hai DBMS mein?

Simple shabdon mein:

Schema ek design ya blueprint hota hai database ka — jisme decide hota hai ki kaunsa data store hoga, kaise organize hoga aur kaise ek data dusre data se juda hoga.

Jaise ek building ka blueprint hota hai, waise hi database ka bhi blueprint hota hai — jisko hum Schema bolte hain.

 Schema = Structure + Organization of database

 Example:

Agar hum ek Library ka database banate hain:

• Tables: Books, Members, Borrow Records

• Tables ke andar kya hoga:

  • Books → Book_ID, Title, Author

  • Members → Member_ID, Name, Address

  • Borrow → Member_ID, Book_ID, Borrow_Date

 Yeh pura design ya naksha hi Library ka Schema hai.

 Simple Diagram:

Library Database Schema:

[Books]                        [Members]
Book_ID       <—>        Member_ID
Title                             Name
Author                         Address

           \                           /
             \                       /
               \                   /

                  [Borrow]
                  Member_ID
                  Book_ID
                  Borrow_Date

• Boxes = Tables hain.

• Arrows = Connections (relationships) hain.

• Schema = Pura design + relationships ka diagram.

 DBMS mein Schemas ke Types

DBMS mein generally 3 Levels of Schema hote hain:

Chalo sabko ek ek karke simple words mein samajhte hain:

 External Schema (User View)

• Har user apna alag view dekh sakta hai database ka.

• Sabko poora database nahi dikhaya jaata, sirf unka relevant part dikhaya jaata hai.

 Example:

• Student apne khud ke marks dekh sakta hai.

• Teacher apne subject ke sab students ke marks dekh sakta hai.

 External Schema = Customized view for different users.

 Conceptual Schema (Logical View)

• Database ka poora logical design hota hai.

• Kya data store hoga, kaise tables ke beech relation hoga — yeh sab define karta hai.

• Storage kaise ho raha hai, yeh nahi dikhata.

 Example:

• Books table mein Book_ID, Title, Author honge.

• Borrow table mein Member_ID aur Book_ID honge.

 Conceptual schema = Poora logical naksha.

 Internal Schema (Physical View)

• Yahan define hota hai ki data physically storage mein kaise rakha gaya hai.

• Files ka format, indexes, kaunse storage devices use ho rahe hain — sab details isme aati hain.

 Example:

• Books table ka data ek file “Books.dat” mein store ho sakta hai.

• Fast searching ke liye indexes banaye ja sakte hain.

 Internal schema = Database ke andar ki actual storage ka plan.

 Real Life Analogy (Simple Example)

Socho ek ghar ban raha hai:

Bilkul waise hi database ka design bhi kaam karta hai!

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 Short Summary Table

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 Important Points:

• Schema = Blueprint ya plan of Database.

• Schema jyada change nahi hota, but data daily change ho sakta hai.

• Database banane ka first step = Schema design karna hota hai.

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 Ek Practical Example (Library Database)

• PK = Primary Key (unique id)

• FK = Foreign Key (relation banane ke liye)

 Is pura setup ko hi bolte hain Library ka Schema.