Illegal vs Unwanted States
16 hours ago
- Illegal states are never acceptable, while unwanted states are undesirable but can temporarily exist.
- Unwanted states, like scheduling conflicts or overbooked flights, may not lead to illegal states but still require resolution.
- Systems must represent unwanted states due to external inputs or intentional design, such as airlines allowing overbooking.
- Unwanted states can be necessary for workflows, like double-booking, and users should be alerted to manage them.
- Formally, illegal states violate invariants (always false), while unwanted states involve safety and liveness properties, like network partitions that must eventually heal.