1. The purpose of closed, nested transactions (subtransactions) is to let a series of database operations within a transaction appear as a unit with regard to modifications to the database.
2. Subtransactions are preceded by SUBTRANS BEGIN and closed by SUBTRANS END or SUBTRANS ROLLBACK.
If a subtransaction is concluded with SUBTRANS END, the performed modifications are kept.
If a subtransaction is closed with SUBTRANS ROLLBACK, all modifications made to the database are cancelled. Modifications made by subtransactions contained in this subtransaction are cancelled as well, even if they have been concluded with SUBTRANS END.
3. SUBTRANS END and SUBTRANS ROLLBACK have no influence on locks. These are only released by COMMIT or ROLLBACK. COMMIT or ROLLBACK implicitly close all subtransactions.