Converting ER Diagram to Tables in DBMS

 Pehle Samjho: Kya aur Kyun?

ER (Entity-Relationship) diagram ek conceptual design hai, jisme hum real-world cheezein (like Student, Course) ko entities, attributes, aur relationships ke form mein dikhate hain.

Lekin database banane ke liye humein is design ko tables mein badalna padta hai, taaki hum data ko store kar saken.

 Step-by-Step Conversion Process

 Step 1: Entities ko Table mein Convert karo

Jo bhi entity hoti hai ER diagram mein, usko ek table bana dete hain.

 Example:

Entity: Student
Attributes: StudentID, Name, Age

Toh Table banega:

 Step 2: Relationship ko Convert karo

Agar relationship Many-to-Many hai, toh uske liye nayi table banate hain.

 Example:

Entities:

• Student (StudentID, Name, Age)

• Course (CourseID, CourseName)
  Relationship: Enrolls (with EnrollmentDate)

Enrolls ka Table banega:

Is table mein dono entities ke primary keys ko foreign key bana dete hain, aur extra attribute bhi add kar sakte hain.

 Step 3: Weak Entities ka Handle

Weak entities woh hoti hain jinke paas khud ka primary key nahi hota. Yeh kisi strong entity pe depend karti hain.

 Example:

Dependent → depends on Employee

Table banega:

 Step 4: Multi-Valued Attributes

Agar kisi entity ka attribute multiple values store karta hai (jaise phone numbers), toh uske liye naya table banate hain.

 Example:

Student ke paas multiple phone numbers hain.

Toh naya table banega:

 Step 5: Generalization / Specialization ka Handle

Agar ek entity ke multiple specific types hain, toh:

• Ek table hota hai general entity ke liye

• Har specific entity ke liye alag table banta hai, jisme foreign key hoti hai general table ka reference.

 Example:

Employee general hai
Manager aur Engineer specific roles hain

Tables:

 Summary Table 

 Example ER Diagram se Table me Conversion :

 

Tables banenge:

• Student(StudentID, Name, Age)

• Course(CourseID, CourseName)

• Enrolls(StudentID, CourseID, EnrollmentDate)

 Conclusion 

• -> ER diagram ek design hai, jisko relational model (table format) mein badalna padta hai.

• -> Har entity → ek table

• -> Har attribute → ek column

• -> Relationship → foreign keys ya naya table

• -> Special cheezein (multi-valued, weak entity) → handled with care