Introduction to DBMS

Introduction to DBMS

Database Management System (DBMS) is software for managing databases. Understanding DBMS concepts is essential for GATE CS.

What is a Database?

Database is a collection of related data organized for efficient access and management.

Database Management System (DBMS) is software that:

• Manages database structure
• Provides data access
• Ensures data integrity
• Handles concurrent access
• Provides security

Database vs File System

Data Models

1. Hierarchical Model

• Tree structure
• Parent-child relationships
• One-to-many relationships

2. Network Model

• Graph structure
• Many-to-many relationships
• More flexible than hierarchical

3. Relational Model

• Tables (relations)
• Rows (tuples)
• Columns (attributes)
• Most widely used

4. Object-Oriented Model

• Objects and classes
• Inheritance
• Encapsulation

DBMS Architecture

Three-Schema Architecture

1. External Schema (View Level)

• User views
• Multiple views for different users
• Hides complexity

1. Conceptual Schema (Logical Level)

• Database structure
• Entities, relationships, constraints
• Database administrator view

1. Internal Schema (Physical Level)

• Storage details
• File organization
• Indexing

Data Independence

Physical Data Independence:

• Changes in physical storage don't affect logical schema
• Example: Changing file organization

Logical Data Independence:

• Changes in logical schema don't affect external views
• Example: Adding new table

Database Languages

1. DDL (Data Definition Language)

• Define database structure
• CREATE, ALTER, DROP

2. DML (Data Manipulation Language)

• Manipulate data
• SELECT, INSERT, UPDATE, DELETE

3. DCL (Data Control Language)

• Control access
• GRANT, REVOKE

4. TCL (Transaction Control Language)

• Control transactions
• COMMIT, ROLLBACK, SAVEPOINT

GATE CS Weightage

DBMS typically accounts for:

• 8-12 marks out of 100 in GATE CS
• Medium priority subject
• Requires conceptual understanding

Important Topics for GATE CS

1. ER Model (High Priority)

• Entity-relationship diagrams
• Relationships and cardinality

1. Normalization (High Priority)

• Normal forms (1NF, 2NF, 3NF, BCNF)
• Functional dependencies

1. SQL (High Priority)

• Queries, joins, subqueries
• Aggregate functions

1. Transactions (High Priority)

• ACID properties
• Concurrency control

1. Indexing (Medium Priority)

• B-trees, hash indexing