How to distinguish a relational database from a document-oriented one and what are their main differences?

A relational database (RDB) and a document-oriented database are different types of data management systems with different structures and approaches.

Relational Database:

• Stores data in tables with clearly defined schemas (rows and columns).
• Uses SQL for queries.
• Supports relationships between tables through keys (primary and foreign).
• Well-suited for structured data with relationships.

Document-oriented Database:

• Stores data as documents (usually JSON, BSON, XML).
• No fixed schema; document structure can vary.
• Queries are executed through special APIs or query languages, for example, MongoDB uses its own query language.
• Convenient for storing semi-structured data and flexible when changing the structure.

Main differences:

• Data structure: tables vs documents.
• Schema: fixed vs flexible.
• Query language: SQL vs specialized APIs.

Example: if you need to store user data with different sets of attributes, a document-oriented database would be more convenient. If complex relationships and transactions are important, a relational database is better.