There is no public Schema description so far and I doubt there will ever be one.
Also saw HP changing the IDB Interna quite frequently with hotfixes, your Queries may therfore be short-lived.
We also need extensive Reports for our Customers and ended up using the session_objects Report, executed for each Backup-Type Session.
Uploaded to a separate DB it allows pretty much every Summary we need without impact to the Backup-Operation and even back several years for trend analysis.