I don't believe that the database schema is published.
That's not to say that a decent DB developer couldn't figure it out.
When I queried IBM about it, years ago, they recommended that people not connect directly to the database. Mostly for performance reasons. They recommend you use the Web Reports interface (you can export report data in a CSV format if you want to manipulate it in another program) or if you have complicated needs, you can access the database via either the SOAP or REST API's. The API's are very powerful, but you need to understand "Session Relevance" to use them properly. I'd recommend you start with the Web Reports interface first since it's much more 'user friendly'. There is a scheduling system in it to allow you to automate the data exports if needed.