Validators can be
used for other jobs as well as displaying interactive data:
If you want to implement an error-recovery system, you could create
View that writes every change to a log file and
then can roll backward and forward through the log (edits are
reversible; renaming is not). This provides a full audit trail,
invaluable when making lots of minor corrections at year-end.
If the system were holding real data (e.g., as part of an executive information system), you could build a system of alerts to warn people or generate certain reports if accounts fell below certain levels, or if creditors were more than a certain amount of time overdue.