>I am affraid of transaction problems in my application, how can avoid this?

if you use delphi, a transaction control can be done like this.

Database1.STARTTRANSACTION;

1.dosomething with the database;
2.dosomething else with the database;
3.dosomething more with the database;

if everything's ok till here,

Database1.COMMIT else Database1.ROLLBACK;


if you rollback, the changes done on the database will be discarded.

untill you commit, other user won't be able to see what you do.