1. A transaction is a sequence of database operations which form a unit with regard to data backup and synchronization. Transactions are closed with COMMIT or ROLLBACK. If a transaction is closed with COMMIT, all modifications made to the database within the transaction are kept. If a transaction is aborted with ROLLBACK, all modifications made to the database within this transaction are cancelled, even those terminated with SUBTRANS END (see 'Subtransaction'). Modifications closed with COMMIT cannot be cancelled with ROLLBACK.
COMMIT and ROLLBACK implicitly open a new transaction.
2. ADABAS distinguishes between SHARE and EXCLUSIVE locks. SHARE locks prevent locked tables or table rows from being modified by other users, although read access is still possible. EXCLUSIVE locks prevent the locked data objects from being read or modified by other users, while the user who has specified the lock can modify the objects.
3. The locking of tables and table rows within a transaction is done with a lock mode determined when the user connects to ADABAS.