OpenGroupware.org uses standard SQL databases as a storage backend for most of it's data. In contrast to various other solutions OGo uses a highly structured and human readable database schema.

Note that the OpenGroupware.org database schema is not supposed to change in an incompatible way for minor versions and it did not change that way since SKYRiX 3.
So, we basically only allow "additions" to the schema. The downside is, that the OGo schema currently contains some tables or attributes which are not really used in practice anymore.

Martin Weber was so kind to provide some PostgreSQL database schema files generated by the PostgreSQL autodoc utility.