http://syndie-project.i2p/db.html
To use these alternate schemas, simply use the login command with --db jdbc:hsqldb:hsqls://127.0.0.1:9999/syndie (etc) after starting
up a standalone HSQLDB database configured for remote access. The database schema itself is kept as part of the Syndie source code as src/syndie/db/ddl.txt , and is documented therein. Basically, it has
tables to contain individual channels, messages within those channels, the content
stored in those messages (including attachments and references),...