Tags.
RFID and barcode tags carry the GS1 identifiers an event observes. The tag is where the identifier originates; the event is what the gateway validates, stamps and hashes once that identifier reaches the door.
POST /capturePOST /translate
One identifier, three spellings, one hash.
urn:epc:id:sgtin:0950600.013435.A1-9 // the EPC URN (RFID era)
(01)09506000134352(21)A1-9 // the element string (label)
https://id.gs1.org/01/09506000134352/21/A1-9 // the Digital Link URI
→ normalize → one canonical form → one CBV §8.9 event hashIllustrative: the same tagged unit as an EPC URN, an element string, and a GS1 Digital Link URI. The gateway's Digital Link normalization feeds the CBV §8.9 hash, so all three name — and hash — the same object.
For the engineer reconciling tag data to events.
Identifier drift — the same unit spelled three ways by three systems — is why traces used to need a reconciliation meeting. Normalization before hashing makes the spelling irrelevant: the same observed object is the same event identity, whichever reader produced the string.
Proof, not adjectives. The gateway's conformance tests pass against GS1's normative artifacts. See How for the dimension, and What ships today for the dated ledger.