As-Of Query
Align combined streams to an explicit instant or cut-off time T
An as-of query (or as-of alignment) combines or reads multiple streams against an explicit instant T — materialised snapshot, query cut-off, or repeatable-read transaction — so the consumer knows which moment the composite represents.
Timestamps provide a pragmatic synchronisation point: values likely belonged to the same wall-time neighbourhood when T and alignment method are published. That often yields U-low cross-stream consistency in enterprise use, especially when the read is also serializable at T.
As-of alignment is policy, not magic. Residual clock skew, races between write and read, and causal mismatch across writers still require disclosure. Per-widget “current” refresh without a shared T is not an as-of query.
Contract fields
Producers should publish: as-of instant T, streams included, alignment method (snapshot table, DB isolation level, etc.), and assumed clock domain / max skew.
Corpus stance
A2 — working context: Common mitigation for cross-stream uncertainty; see Why Uncertainty Matters.