Cross-Stream Consistency
Whether a combined view corresponds to a state that could have existed together
Cross-stream consistency is the third component of epistemic uncertainty: whether a view that combines several independent streams corresponds to a state that could have existed together — causally and temporally — at the moment the consumer treats it as one picture.
Each stream may be fresh and accurate on its own while the combined artifact still depicts an impossible simultaneity — balance as of 14:32:07, inventory as of 14:32:04, pricing as of 14:31:58. Common causes include processing lag (different refresh cadences), clock skew, and causal mismatch across writers.
Alignment and guarantees
Producers align streams with policy, not hope: as-of queries, materialised snapshots, disclosed clock domains, and — where infrastructure provides them — serializability or linearizability guarantees. Residual cross-stream error often falls to U-low inside a trusted single system; it may be fatal in closed-loop physical control. Stakes and domain set the threshold.
Processing lag
Independent pipelines finish at different wall times even when clocks agree. Lag is not skew; it is solved by explicit cut-off time and published refresh cadence, not by assuming “current” on each widget means the same instant.
Corpus stance
Context — vocabulary for the uncertainty contract; complements temporal staleness and probabilistic computation loss (η). See Why Uncertainty Matters.