Priorities are available and useful
Priority information is naturally available and useful. E.g.,
- recency: higher priority for more recent updates.
- specificity: higher priority for more specific cases (e.g., exceptional cases, sub-cases, inheritance).
- authority: higher priority for more authoritative sources (e.g., legal regulations, organizational imperatives).
- reliability: higher priority for more reliable sources (e.g., security certificates obtained by delegation, assumptions, observational data).
- closed world: lowest priority for catch-cases.
Many practical rule systems employ priorities of some kind, often implicit, e.g.,
- rule sequencing in Prolog and production rules.