DatabaseDatabase Basics

📚 Database Basics

Learn fundamental database concepts, DBMS architecture, and data models.

DBMS

Software that manages databases — stores, retrieves, and processes data efficiently.

Schema

The logical structure of a database — defines tables, columns, relationships, and constraints.

Data Models

How data is structured: Relational, Document, Key-Value, Graph, and Column-Family.

DDL vs DML

DDL defines structure (CREATE, ALTER). DML manipulates data (SELECT, INSERT, UPDATE, DELETE).

Three-Schema Architecture

External LevelUser View

How individual users view the data. Multiple views for different users.

e.g., A student sees only their grades, not all grades.

Conceptual LevelLogical

The community view — entire logical structure of the database.

e.g., All tables, relationships, constraints defined.

Internal LevelPhysical

Physical storage details — how data is stored on disk.

e.g., File organization, indexes, data compression.

Types of DBMS

Relational (RDBMS)

Data in tables with rows/columns. Uses SQL. Examples: MySQL, PostgreSQL, Oracle.

NoSQL Document

Data stored as JSON-like documents. Examples: MongoDB, CouchDB.

Flexible Schema

NoSQL Key-Value

Simple key-value pairs. Fast lookups. Examples: Redis, DynamoDB.

High Performance

NoSQL Graph

Nodes & edges for connected data. Examples: Neo4j, ArangoDB.

Relationships

Column-Family

Data in column families. Examples: Cassandra, HBase.

Big Data

Advantages of DBMS

✓Controls data redundancy (minimizes duplication)

✓Ensures data consistency across the system

✓Enforces data integrity constraints

✓Provides concurrent access with ACID transactions

✓Offers data security with authentication/authorization

✓Enables data independence (logical & physical)

✓Supports backup and recovery mechanisms

✓Reduces application development time

Interview Questions

Q1: What is a database management system (DBMS)?

A: A DBMS is software that enables users to define, create, maintain, and control access to databases. It acts as an intermediary between users and data.

Q2: What is the difference between DBMS and RDBMS?

A: DBMS stores data as files, while RDBMS stores data in tables with relationships. RDBMS supports ACID transactions, normalization, and uses SQL.

Q3: Explain the three levels of data abstraction.

A: External (user views), Conceptual (logical structure), Internal (physical storage). This provides data independence.

Q4: What is data independence?

A: The ability to change the schema at one level without affecting the next level. Logical independence: changing conceptual schema without affecting external views. Physical independence: changing storage without affecting conceptual schema.

Q5: What are the advantages of using a DBMS?

A: Data redundancy control, data consistency, data sharing, security enforcement, backup/recovery, concurrent access management, and data independence.