Validity Interval

The span over which a fact was true — valid_from to valid_to — as distinct from the span over which the system believed it.

Why it matters in a memory layer

An open valid_to means "still true as far as anyone said", and that is the honest default: nothing in a conversation announces that a fact has ended. Closing the interval is a separate act from retiring the belief, and the two dates are routinely different — she left the job in December and mentioned it in January.

Skip the interval and "what is true now?" has to be answered by proxy, usually by filtering on belief time. On this course's corpus that proxy returns five employer facts where four are live, because without recorded ends every fact stays open. The proxy works only while the two clocks are the same, which is exactly when nobody notices it is a proxy.

Connections

Taught in: Validity Intervals

Used in: Resolving 'Last Week' · Temporal Knowledge Graphs · Three Temporal Questions

Do not confuse with: Supersession