Database Management System

■ Complete DBMS Notes

DBMS Concepts and Architecture
A Database Management System (DBMS) is software that allows efficient management of data.
It provides abstraction and hides complexities of physical storage.
Main goals: data independence, consistency, concurrency, security, and integrity.

■ Three levels of data abstraction:
1. Physical Level – How data is stored (files, indexes).
2. Logical Level – Structure of database (tables, attributes, relationships).
3. View Level – User interaction, hides complexity.

■ Architectures:
- Single-tier: User interacts directly with DB.
- Two-tier: Client ↔ Server.
- Three-tier: Client ↔ Application Server ↔ Database Server.




File Processing System
Before DBMS, applications used a file-based system. Each program managed its own data files.

■ Features:
- Data stored in separate files.
- Programs written for specific tasks (payroll, library, etc.).
- No central control over data.

■ Problems:
- Redundancy and inconsistency.
- Difficulty accessing data.
- Integrity and security issues.
- Concurrent access not supported.

Limitations of File Processing System
1. Data Redundancy – Same data stored in multiple places.
2. Inconsistency – Different copies may mismatch.