I am happy to announce that the first implementation of the DiscourseDB object model is now available on GitHub. [1][2]
The database schema is now auto-generated from the object model via hibernate and a data access layer based on Spring Data JPA allows low-level communication with the database. A high-level API for end users is currently under development.
The currently available pre-release version of DiscourseDB is v0.4 The developer version is 0.5-SNAPSHOT.
Beyond that, a first data converter is now available that imports edX discussion forum data into DiscourseDB [3][4]. Documentation of the mapping between edX json and DiscourseDB is forthcoming.