Databases

Table-based databases using rows, columns, and SQL — PostgreSQL, MySQL, SQL Server, and Oracle all fall into this model.

Non-relational databases built for flexible schemas and horizontal scale — document, key-value, wide-column, and graph stores all fall under this umbrella.

Databases that store data as objects, mirroring the classes and inheritance of an object-oriented programming language directly.

Tree-structured databases where every record has exactly one parent — the model behind early systems like IBM's IMS.

An evolution of the hierarchical model that lets a record have multiple parents, forming a graph instead of a strict tree.

Databases delivered as a managed service — provisioning, scaling, backups, and patching handled by the cloud provider instead of your own ops team.