Relational Databases

Most real-world commercial applications persist their data to a relational database — and with good reason.

Most business systems are not created in a vacuum. Typically, they must interoperate with legacy systems, and they must access legacy data. This means that your customer may specify a particular existing relational database as your persistence mechanism.
Relational database technology is mature. It has been tested, its performance is well understood and there are good tools to support the development and maintenance of large relational database applications.