Most applications use a relational database such as Oracle, MySQL, or PostgreSQL; however, there is more to data storage than just SQL databases. There are also these types:
Document stores (MongoDB, Couchbase)
Key-value stores (Redis, Voldemort)
Column stores (Cassandra)
Graph stores (Neo4j, Apache Giraph)
Each of these technologies (even different implementations of them) has its own purpose. They can also be hard to use or configure, but Spring Boot makes it easier to configure and use them. Spring Boot uses auto-configuration, ...
