The event

One job: read one event and know what every field is for. An EPCIS 2.0 event records one observed moment. The standard defines five dimensions on it — what, when, where, why, how. The event here has six: who — the attested observer — carried as spine:who under a declared JSON-LD context, so the document stays valid against the pinned official schema.

One fixture, annotated by dimension

This event ships in the package at golden-corpus/valid-superset/object-event-attested-observer.json:

{
  "type": "ObjectEvent",
  "eventID": "urn:uuid:8a1b2c3d-4e5f-4a6b-8c7d-0e1f2a3b4c5d",
  "eventTime": "2026-07-19T11:45:00.000Z",
  "eventTimeZoneOffset": "+02:00",
  "epcList": ["urn:epc:id:sgtin:0614141.107346.2021"],
  "action": "OBSERVE",
  "bizStep": "receiving",
  "disposition": "in_progress",
  "readPoint": { "id": "urn:epc:id:sgln:0614141.00999.0" },
  "spine:who": "https://id.org.ai/agents/dock-scanner-7",
  "spine:activity": "https://event-spine.internal/activities/inbound-receiving/run/42"
}

dimension	fields	in this event
What	epcList, action	one serialized item, observed (OBSERVE: seen, not created or removed)
When	eventTime, eventTimeZoneOffset	when it happened, in local wall-clock terms; recordTime — when the door heard — is stamped at capture, never caller-supplied
Where	readPoint, bizLocation	the point that saw it; the business location it speaks for
Why	bizStep, disposition, bizTransactionList, sourceList, destinationList	receiving, in progress — the CBV's vocabulary, not free text
How	sensorElementList	absent here; present when an instrument observed
Who	spine:who	the attested observer — a human, an agent, or an embodied agent; the sixth dimension this spine adds

The standard's own party fields are organisation-grain — GLNs and PGLNs name legal entities, and no standard field names the performer. spine:who carries the performer without forking the schema; the next page, who vs capturedBy, states the two grains exactly.

The event supertype, and the five types

Every field above except epcList and action belongs to the event supertype — the shape all five event types share. The types differ only in their What:

type	its What
ObjectEvent	objects observed, added or removed
AggregationEvent	a parent (the pallet) and its children (the cases) — physical nesting, action ADD/OBSERVE/DELETE
TransactionEvent	objects declared against business transactions
TransformationEvent	inputs consumed, outputs produced — genealogy
AssociationEvent	an assembly relation (a sensor bolted to a reusable asset)

The diff, by dimension

The sixth dimension is exactly what the conformant projection removes — executed 2026-07-31 against the published package:

$ node --input-type=module -e '
  import { readFileSync, writeFileSync } from "node:fs";
  import { project } from "epcis.dev";
  const doc = JSON.parse(readFileSync(
    "node_modules/epcis.dev/golden-corpus/valid-superset/object-event-attested-observer.json",
    "utf8"));
  const ev = doc.epcisBody.eventList[0];
  writeFileSync("event.json", JSON.stringify(ev, null, 2) + "\n");
  writeFileSync("event.projected.json", JSON.stringify(project(ev), null, 2) + "\n");'

$ diff event.json event.projected.json
14,16c14
<   },
<   "spine:who": "https://id.org.ai/agents/dock-scanner-7",
<   "spine:activity": "https://event-spine.internal/activities/inbound-receiving/run/42"
---
>   }

Five dimensions survive projection untouched; the sixth lifts off cleanly. That round-trip discipline is the whole envelope contract — the projection states it, and proves the projected event validates against the pinned official schema.