Historical recall

Taisce keeps two kinds of time for every fact: when it was true, and when Taisce knew it. You can ask a question at any point on either axis and get the answer as it stood then.

Ask about the past

Add one or both timestamps to a recall (RFC 3339 format):

POST /v1/recalls
Authorization: Bearer <credential>
Content-Type: application/json

{
  "question": "Where did I live?",
  "data_subject_id": "subject-1",
  "as_of": "2026-08-01T00:00:00Z",
  "as_known_at": "2026-03-10T00:00:00Z"
}

• as_of picks the moment the claim was true.
• as_known_at picks what Taisce knew at that moment.
• Leave out as_known_at to use current knowledge.
• Leave out both to get what is true now.

An example

Suppose you record "lives in Dublin" in March, then "lives in Amman from June" in July.

Question	as_of	as_known_at	Answer
Where did I live in August?	August	before July	Dublin, no end date
Where did I live in August?	August	now	Amman
Where did I live in April?	April	now	Dublin, ending in June
Where did I live in April?	April	before July	Dublin, no end date

The first row is useful for audits: it shows exactly what an agent would have been told before the move was recorded.

Look at one fact's history

Fact IDs stay the same when a newer fact supersedes them. To see every interval one fact has had, use record history. Citation inspection shows the fact as it is now, with superseded_by and supersession_source_observation_id when it was replaced. Subject exports include every stored interval in their fact_history section.

Watch out for

• History starts at install time. A query for knowledge from before anything was recorded returns no facts, even if an entity with that name exists now.
• Erasure removes history too. Erasing a subject or letting retention expire their data removes earlier versions as well. If the message that set a fact's end date is erased, that fact can become unavailable even though its original message survives.
• You can't take back an answer. A response already sent to a client stays sent.
• Only facts are versioned. Historical recall keeps each fact's intervals. It does not keep old entity names, old alias lookups, or an exact copy of an earlier API response.
• Corrections apply to current records only. You can correct or retract a record that is still current, and history keeps the original. You can't edit a record that has already been closed.

How it works

Each fact has a validity interval and a knowledge interval. When a new fact supersedes an old one, Taisce closes the old fact's intervals and copies the closed version into a history table. The live fact keeps its ID. A historical recall reads whichever version was open at the times you asked for.

If a fact's closing message is erased, Taisce won't guess the end date. The fact stays unavailable until a new source establishes it again.