Skip to content

Correspondence Validation

Ensure a new model, theory, version, or system matches the old one within the old one’s valid domain before replacing it.

The Diagnostic Story

Symptom: A newer model, version, rule, or system is proposed to replace an older one. The replacement is validated on its own terms — it is accurate, well-tested, broadly applicable — but nobody has checked whether it reproduces the older system's trusted behavior in the cases where the old system was already known to work. When the replacement goes live, regressions appear in exactly those cases.

Pivot: Before adopting the replacement, state the predecessor's valid domain explicitly, compare the candidate inside that domain, and classify any divergence as legitimate extension or unacceptable regression. That test governs whether the replacement is adopted as-is, revised, scoped, or rejected.

Resolution: Users and decision-makers retain continuity with trusted behavior in known regimes while the new system extends or modernizes beyond them. Replacement decisions are grounded in a documented overlap test, and regressions inside the predecessor's valid domain are caught before commitment rather than after deployment.

Reach for this when you hear…

[regulatory compliance] “The new classification system was more rigorous overall, but it systematically miscategorized a class of cases that the old system had handled correctly for a decade.”

[software version migration] “The rewritten API was cleaner, but the team only tested new use cases — nobody checked that the old integrations still worked until the migration was live.”

[clinical guidelines] “The updated protocol improved outcomes on average, but it produced worse outcomes for the specific population the old guideline was designed for.”

Mechanisms / Implementations

  • Backward Compatibility Test: Checks that a new version still honors every promise existing consumers already rely on, so an internal change can ship without breaking anyone downstream.
  • Divergence Review Workflow
  • Golden Case Benchmark: A curated library of canonical input-to-output cases, captured from the current system, that serves as the fixed reference for judging whether a refactor changed observable behavior.
  • Migration Acceptance Test
  • Model-Limit Validation
  • Protocol Conformance Test
  • Regression Test Suite: Re-runs a corpus of previously-passing cases against each new version so that any unintended loss of working behaviour breaks the build, using the system's own recorded past output as the reference.
  • Shadow Run or Parallel Run: Runs the new implementation alongside the old on live traffic — old system serving, new system shadowing — and compares their outputs and real-world side effects before trusting the new one to take over.

Abstractions this archetype builds on — directly (a source ingredient) or as a related pattern. Links follow the typed catalog namespace.

Built directly on (2)

Also references 9 related abstractions

Variants

Narrower or domain-specific specializations that share this archetype's core structure. Recognized variants are established; candidate variants are provisional.

Backward Compatibility Validation · implementation variant · recognized

Validate that a new version preserves existing behavior, interfaces, or user expectations where old compatibility is still promised.

Model-Limit Correspondence · subtype · recognized

Validate that a newer or broader model reproduces the older model under the older model’s domain of validity or limiting conditions.

Migration Correspondence Validation · temporal variant · recognized

Validate old-new continuity during a migration so users, data, obligations, and operational behavior survive the transition.