Databases are typically classified as relational (SQL) or NoSQL, and transactional (OLTP), analytic (OLAP), or hybrid (HTAP). Departmental and special-purpose databases were initially considered huge improvements to business practices, but later derided as “islands.” Attempts to create unified databases for all data across an enterprise are classified as data lakes if the data is left in its native format, and data warehouses if the data is brought into a common format and schema. Subsets of a data warehouse are called data marts.
