How do relational databases differ from non-relational data storage systems?

Relational databases (RDB) and non-relational data storage systems (NoSQL) differ in several key aspects:

• Data Structure:

  • RDBs use tables with a fixed schema (rows and columns), where data is linked through keys.
  • NoSQL can use various models: documents (JSON), key-value, graphs, column stores, without a strict schema.

• Schema:

  • RDB schema is rigidly defined and requires migrations when changes occur.
  • NoSQL schema is flexible or absent, which is convenient for rapidly changing data.

• Scalability:

  • RDBs typically scale vertically (adding resources to a single server).
  • NoSQL is often designed for horizontal scaling (adding more servers).

• Transactions and Consistency:

  • RDBs support ACID transactions, ensuring strict consistency.
  • NoSQL often sacrifices strict consistency for performance and availability (eventual consistency model).

• Examples:

  • RDB: MySQL, PostgreSQL, Oracle.
  • NoSQL: MongoDB (documents), Redis (key-value), Cassandra (columnar).

The choice between them depends on data requirements, speed, scalability, and consistency.