Changes are controlled so as to increase the assurance that
they are valid. Examples include change control systems for software,
roll-back and back-out capabilities for updates, and strong change control
processes in use in select critical applications.
Complexity: Proper change
control demands that, in the production system, no programming capability be
available. The verification of the propriety of changes is complex and, in
general, may be comparable to proof of program correctness which is well
known to be at least NP-complete.