Explain the different Relational Model constraints

Explain the different Relational Model constraints

Answer:-

In the Relational Model of DBMS, constraints are rules that ensure data accuracy, integrity, and consistency in a database.

There are 4 main types of relational model constraints:

1. Domain Constraints

• Restrict the type of values that attributes (columns) can hold.
• Each attribute must contain only values from a defined domain (data type or range).
• Example:
  • Age must be an integer between 0 and 120
  • Email must be a string (varchar)

2. Key Constraints

• Ensure uniqueness of rows (tuples) in a table.
• There are two types:
  • Primary Key: Uniquely identifies each row. Cannot be null.
  • Candidate Key: A set of fields that could serve as a primary key.
• Example:
  • In Students(RollNo, Name, Age), RollNo is the primary key.

3. Entity Integrity Constraint

• States that primary key of a table cannot be null.
• Because each entity (row) must be uniquely identifiable.
• Example:
  • If EmployeeID is a primary key, it must have a value for every employee.

4. Referential Integrity Constraint

• Ensures that a foreign key in one table correctly refers to an existing primary key in another table.
• Prevents orphan records (i.e., references to non-existent rows).
• Example:
  • If Orders(CustomerID) references Customers(CustomerID), every CustomerID in Orders must exist in Customers.

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