Denis Simonov is the author of Firebird documentation, seasoned developer and DBA.

Denis Simonov sells the following books and courses in FirebirdSQL shop:

1 . Book: Detailed new features of Firebird 5, 2nd edition (purchase: €16.99 / US$19.99)

2. Book: Coming soon!  Secrets of Firebird Query Optimizer (pre-order will be available soon)