Neo4j

Neo4j is a native graph database. It stores data as nodes and relationships, not tables or documents. It is essential for "connected data" problems where relationships are as important as the data itself.

When to Use

• Knowledge Graphs: Connecting silos of data (Users, Docs, Concepts).
• Fraud Detection: Finding "Rings" of users sharing IDs/Devices.
• Recommendation Engines: "People who bought X also bought Y" (Collaborative Filtering).
• GraphRAG (2025): Enhancing LLM context by traversing a knowledge graph instead of just vector similarity.

Quick Start (Cypher)

-- Create nodes and relationships
CREATE (alice:Person {name: 'Alice'})
CREATE (bob:Person {name: 'Bob'})
CREATE (alice)-[:KNOWS {since: 2024}]->(bob);