Exceptions

After this lesson, the reader should understand:

• 01Distinguish an exception from a condition and from a waiver.
• 02Express precedence between a rule and its exceptions.
• 03Handle exceptions granted by a different authority.

The standing emergency exemption

An exemption granted for an emergency is still in force four years later. Why?

Because nothing in the document expressed an expiry, and nothing in the process re-evaluated the trigger. As an artifact, the exception carries its own conditions and an expiry, and the runtime stops applying it when the conditions no longer hold. The failure was not the exemption — it was expressing a temporary displacement in a form with no notion of time.

• Should exceptions ever be permanent?
• Who audits the population of live exceptions?
• How do overlapping exceptions resolve?

Model one exception completely.

1. 01Name the rule it displaces.
2. 02State its trigger conditions precisely.
3. 03Name the granting authority and the expiry.
4. 04Describe what happens on expiry.

• Defeasible reasoning and priority orderings.
• Administrative law on waivers and derogations.
• Exception handling in safety-critical specification.