Database Overview | Notion

Definition & Purpose

Database: An organized collection of structured data managed by a DBMS (Database Management System).

Primary Goals

Data persistence
Efficient retrieval and modification
Ensuring data integrity and safe concurrent access

Database Models: Relational (SQL)

Structure: Tables (rows & columns), defined by a fixed schema

Keys

Primary Key: Unique identifier for each row
Foreign Key: Enforces referential integrity between tables

Transactions & ACID

Concept	Explanation
Atomicity	All-or-nothing operations
Consistency	Data remains valid after transactions
Isolation	Non-interfering concurrent transactions
Durability	Committed changes persist after failures

Database Models: NoSQL

Characteristics: Schema-flexible, horizontally scalable
CAP Theorem: Trade-off among Consistency, Availability, Partition tolerance

Categories

Category	Example	Description
Key–Value Store	Redis	Simple get/put on key
Document Store	MongoDB	JSON-like documents
Column-Family Store	Cassandra	Wide, sparse tables
Graph Database	Neo4j	Nodes & edges for relationships