Expand description
External-expectation generator — the ISA-520 substantive-analytics layer (Phase 2).
Emits, per material GL account, an ExternalExpectation: an expected period total derived from
an exogenous driver (prior-year / market / macro / budget) plus a materiality tolerance band, the
realized deviation, and the ground-truth fraud contribution.
The expectation is anchored to the account’s legitimate level (the sum of its non-fraud
postings) perturbed by a forecast error — modelling a real auditor’s prior-year/benchmark
expectation, which tracks the legitimate economics but is imprecise. A mimetic fraud preserves the
per-entry ledger distribution (so the per-JE residual arms are blind) yet inflates the account’s
aggregate above this expectation: a band exceedance is the ISA-520 “investigate” trigger, and is
a true positive iff the account was in fact fraud-inflated (the engine knows). This is the
engine-side realization of the perfect-crime countermeasure (docs/phase2-ledger-evidence-assurance.md).
Structs§
- Account
Actuals - Per-account input to the expectation generator: the realized totals split into legitimate vs actual.
- External
Expectations Generator - Generates
ExternalExpectationrecords for a company’s material accounts.