The primary target technology for the database is Postgres.
The entity extensibility mechanism is implemented using the JSONB feature of Postgres.
Other database support:
SQL-Server
Existing implementation of openIMIS make use of SQL-Server database.
The migration strategy puts the database migration to final stages (to ensure an iterative approach).
Early version of openIMIS supports SQL-Server.
(To be validated) The extensibility mechanism makes use of SQL-Server JSON feature.
Other
Support of other databases must be studied on case-pre-case basis. The use of an ORM framework (Django) is of great help in this area.
However, being database vendor-agnostic is not an easy task and requires many precautions.