Databases and APIs

Databases fall broadly into two families that organize data on different premises. Relational databases store data in tables made of rows and columns, with a rigid, predefined schema and relationships between tables enforced through keys, and they are built around strong consistency guarantees summarized by the acronym ACID (atomicity, consistency, isolation, durability). Non-relational, or NoSQL, databases relax that rigidity in favor of flexible schemas and, often, horizontal scalability across many machines, storing data instead as documents, key-value pairs, wide columns, or graphs depending on the specific system. Neither family is a strict upgrade over the other; the choice depends on whether an application's data is naturally tabular and relationship-heavy, whether the schema is expected to change frequently, and how the system needs to scale as data volume grows.