Relational Model

1. What is Relational Model?

The relational model organizes data into relations (tables). Each table consists of tuples (rows) and attributes (columns).

• Simple and easy to understand
• Based on mathematical relations
• Uses SQL for data manipulation

2. Basic Terminology

Relation   → Table
Tuple      → Row
Attribute  → Column
Degree     → Number of attributes
Cardinality→ Number of tuples

3. Example of a Relation

STUDENT
+---------+--------+-------+
| RollNo  | Name   | Marks |
+---------+--------+-------+
| 101     | Amit   | 78    |
| 102     | Riya   | 85    |
| 103     | Suman  | 72    |
+---------+--------+-------+

Degree = 3
Cardinality = 3

4. Domains

A domain defines the set of valid values that an attribute can take.

• RollNo → Integer
• Name → Character string
• Marks → Integer (0–100)

5. Relational Schema

A relational schema defines the structure of a relation including its name and attributes.

STUDENT (RollNo, Name, Marks)

6. Properties of Relations

• No duplicate tuples
• Order of rows and columns does not matter
• Each attribute has atomic values
• Unique attribute names

7. Keys in Relational Model

Keys are used to uniquely identify tuples in a relation.

• Super Key
• Candidate Key
• Primary Key
• Foreign Key

STUDENT
RollNo → Primary Key

8. Integrity Rules

• Entity Integrity: Primary key cannot be NULL
• Referential Integrity: Foreign key must match primary key

9. Advantages of Relational Model

• Simple structure
• Flexible querying using SQL
• Strong data integrity
• Easy database maintenance

10. Limitations of Relational Model

• Performance issues with very large databases
• Not ideal for complex multimedia data
• Requires joins for related data

Practice Questions

1. Define relational model.
2. Explain basic terminology of relational model.
3. What is degree and cardinality?
4. Explain integrity rules.
5. List advantages of relational model.

Practice Task