What is the purpose of non-relational databases and in what cases are they used?

Non-relational databases (NoSQL) are designed for storing and processing data that doesn't fit into traditional relational table structures. They are used when high scalability, flexible data models, or handling large volumes of unstructured data are required.

Main use cases:

• Document storage (e.g., JSON) — MongoDB
• Key-value for caching and fast queries — Redis
• Graph databases for complex relationships — Neo4j
• Columnar databases for analytics — Cassandra

Example: if you have a dynamically changing data structure or need to scale quickly, NoSQL might be preferable over relational databases.