Concepts · 2 of 5
Three-valued truth
Every claim has one of three values. The difference between "contradicted" and "not yet established" decides what should happen next, so the two are never collapsed. Missing or stale evidence is never a contradiction.
Three-valued truth
| Value | Meaning |
|---|---|
| TRUE | Applicable evidence establishes the claim's predicate. Only TRUE satisfies a positive requirement. |
| FALSE | Applicable evidence contradicts the predicate. The claim is refuted, not merely open. |
| UNKNOWN | The applicable evidence is not enough to decide. Something should be observed before anything is concluded. |
More columns: swipe horizontally, or focus the table and use the arrow keys.
Examples
These come from the design document.
| Situation | Value |
|---|---|
| The check was never run | UNKNOWN |
| The check ran and failed | FALSE |
| The check ran and passed | TRUE |
| It passed for revision R1; the current revision is R2 | UNKNOWN |
| An observation is older than the protocol allows | UNKNOWN |
More columns: swipe horizontally, or focus the table and use the arrow keys.
What exists today
canon evaluate gives every claim of a case one of the three values from its evidence records. An
evidence match with a result is unknown when no record of the kind exists, false when records
exist and none has the result, true when every record of the kind has that result, and unknown
when records of the kind disagree. A match that names a subject counts only the records about
that artifact. The evaluation reference has every
rule, and the worked example shows the values for five
evidence situations.
A record bound to a revision of its artifact that is not the case's current one is left out of claim evaluation, so the R1/R2 row is UNKNOWN as shown.
A record older than its evidence kind's max_age at the evaluation instant (canon evaluate --at) is left out of claim evaluation, so the last row is UNKNOWN as shown.