When you're ready to store/delete data, precede the Set/Kill statements with a TStart command, and place a TCommit command afterwards. This marks the Set/Kill statements as a transaction. If the system happens to crash during a transaction, the system (when it returns to operation) will roll back (cancel) the incomplete transaction. Either the entire transaction completes, or none of it does.
As you'll learn in the next section, save and delete operations on Caché Objects or SQL Tables are automatically performed inside a transaction.