A finished trade does not stay private between the two firms that struck it. Each side has to hand a record of it to a regulator — sometimes directly, sometimes into a shared store called a trade repository — so the market can be watched and, when needed, reconstructed. Where that record goes, and whether both sides report it, depends on what was traded.
A trade earns its identifiers at the moment of execution — the codes that name the deal, the product, and the parties, set out in the lesson on the trade record and its identifiers. Reporting is the step that follows: the named record is submitted so authorities can aggregate it, watch the market, and, when needed, reconstruct events. Which route it takes depends on the instrument.
For derivatives, the record goes to a trade repository, a central store built for the purpose. Its defining feature is that both counterparties report, each from its own side. The shared Unique Transaction Identifier (UTI) is what lets a regulator pair those two independent reports into a single trade. That two-sided design is the source of much of the reconciliation effort that follows: when the two sides disagree, the reports fail to pair.
Cash equities take a different route. In Europe, the executing firm reports the transaction to its national regulator under Article 26 of the Markets in Financial Instruments Regulation (MiFIR) — one report, from one side. In the United States, order and execution events flow into the Consolidated Audit Trail, linked by keys rather than paired by a UTI. The same event, lodged in different stores under different logic.
Whatever the route, the reported record is a standardized set of fields — for derivatives, the globally harmonized Critical Data Elements — so that authorities can aggregate across firms and repositories. That aggregation is the whole purpose, and its limits, once a trade crosses borders, are the subject of the essay The codes travel; the data stays home.