Valid time

Valid time answers when a fact held in the represented domain, according to the available evidence. It may be a point, an interval, an open-ended period, or unknown. A contract effective date, for example, can differ from the date the contract was signed, received, or entered into a system. Valid time is a property of the assertion being made, so two assertions from the same document can have different valid periods.

A practical record names the source and the rule used to interpret its temporal language. Retroactive amendments and notices received late require particular care: they may alter the current account of an earlier interval. An unknown start or end should remain unknown rather than being replaced by the first or last date on a file. Explicit interval boundaries make overlap and succession checks interpretable across systems.

For a defensible decision, valid time identifies whether a value applied on the decision's target date. It does not identify when the organization learned that value; transaction time serves that separate question. Pairing the two avoids projecting today's corrected understanding into a past information state. An as-of query can then specify the date being assessed while making clear which recorded knowledge state it uses.

A period needs a start, an end and a convention. Half-open intervals, which include the start and exclude the end, avoid the gaps and overlaps that occur when one period ends on the day another begins. Dates and times should follow a standard format such as that in RFC 3339, with a stated time zone where times matter. Where the true boundary is unknown, record the earliest and latest possible values and not a guess. Interval relations such as before, overlaps and during, formalised in the temporal reasoning literature, are the basis of queries like which statements were true at the same time.

Constraints help. For a property that can have only one value at a time, such as legal name, the periods for that entity and property should not overlap; a check for overlaps finds data errors. For properties that can have several values, such as directors, overlap is normal. The Wikipedia article on temporal databases surveys these ideas. Where a source gives no period, the claim should say so and should not be assigned the retrieval date as its start.

For ten sampled facts, ask for the period during which each held and where the dates came from. Check that no date in the valid-time field is a retrieval or publication date by default. Check that the interval convention is documented and applied. Test an overlap query on a single-valued property. Test a date known to fall in a gap and confirm that the system reports no value and not the nearest one.