Time Travel: A Pattern Language for Values That Change

You get a raise on 1 March but the system doesn’t find out about it until mid-May. In the meantime, who knows what happens? Reconciling these two time lines, world time and system time, is one of the most difficult problems to solve in writing information systems. Many of the actions in business are irreversible. It is complicated and expensive to take an incorrect check back. To “make the check right”, you must discover what happened and to fix the situation.