Single source of truth

Single source of truth describes an arrangement in which a defined value has an agreed account for its intended consumers. It is an aspiration about consistency and authority, not a claim that the world supplies only one source of evidence. Multiple documents can legitimately disagree, and different time frames can yield different valid answers. A meaningful claim of singularity therefore names the fact, scope, time, and rule by which an account is accepted.

In practice, downstream copies should identify the governing source and their refresh point. Disputed or unresolved values need explicit states rather than a fabricated single answer. A correction process should show what changed and why, so consumers can understand whether their earlier decisions used the former account. An organization may designate several systems of record for different domains while still presenting one governed view of each fact to its users.

The phrase is useful only when it helps a reader locate and challenge an accepted value. If it hides conflicting source claims, it weakens rather than strengthens defensibility. Provenance and data lineage show how a displayed value relates to evidence; bitemporal data distinguishes a present account from what was previously known. A system of record names the authority for a scope, while a single source of truth describes the intended consistency seen by consumers.

Some facts have more than one legitimate account. A fact that changes over time has several, each true for a period, and a bitemporal record keeps all of them; a single current value discards the rest. A fact on which sources disagree may need the disagreement preserved and shown. A contested classification, such as the category of an organisation, may differ by purpose. Forcing one account on such facts hides information. The article on multiple sources of truth tests the assumption fact by fact, and the one on merging or relating organisation records shows an alternative that keeps records distinct and links them.

A workable principle is that the single source should be single for the question asked, with its scope, date and rules stated, and with a way to see the other accounts when they differ. The knowledge-graph design described by Wikidata, which stores multiple statements with ranks and references, shows one implementation of this principle for an open collaborative dataset.

For a headline figure, ask for its definition, its source and its reconciliation to the nearest other source. Ask who may change the definition. Ask how disagreement between systems is detected. Ask for the figure as it was at the last reporting date. Look for copies of the figure in spreadsheets that are edited by hand.