In our case, the database is implemented with the PostgreSQL database system. PostgreSQL is a relational database management system. While arguably not as common as MySQL installations, larger enterprises may prefer Oracle databases. PostgreSQL is, in any case, a robust system, and our example organization has chosen PostgreSQL for this reason.
From a DevOps point of view, the three-tier pattern looks compelling, at least superficially. It should be possible to deploy changes to each of the three layers separately, which would make it simple to propagate small changes through the servers.