The decision about a database depends on the approach. Here two approaches are compared. To achieve this goal, everyone must use the same approach.
Oracle NO-SQL
Commercial database-systems are unsuitable for open source projects.
This decision based on the experience and knowledge of the students.
Many projects use a Relational DB! We are already use it temporary in the integrated memory database (h2).
The project team is familiar with relational databases. It would be an extra effort to learn a new technology (No-SQL). In addition, the integration from the H2 memory database to another e.g. MySql is much easier, because MySql is also a relational database.