Verbs & vocabulary

Every statement names what happened with a verb. Verbs are URIs, the registry is descriptive rather than prescriptive, and Empress never rejects a statement because it hasn’t seen the verb before.

Verbs are URIs

In xAPI, a verb is identified by a URI, not a bare word. The URI makes the verb globally unambiguous: http://adlnet.gov/expapi/verbs/completed means the same thing in every tenant’s ledger, while two teams using the plain word “completed” might mean different things. A human-readable display name rides along in the statement, but the URI is the identity.

"verb": {
  "id": "http://adlnet.gov/expapi/verbs/completed",
  "display": { "en-US": "completed" }
}

The any-verb principle

Ingestion validates structure, never vocabulary. A well-formed statement with a verb Empress has never seen is stored and becomes queryable, exactly like one using a registered verb. The intelligence about what verbs mean lives in the analytics layer, where it can improve without ever having rejected data it didn’t yet understand. The registry below is documentation of what’s in use — it is not an allowlist.

Common registered verbs

These come from the canonical registry — a mix of ADL core and community vocabularies that cover most learning and interaction events.

Verb	URI	Meaning
completed	`http://adlnet.gov/expapi/verbs/completed`	Finished an activity
passed	`http://adlnet.gov/expapi/verbs/passed`	Met success criteria
failed	`http://adlnet.gov/expapi/verbs/failed`	Did not meet success criteria
scored	`http://adlnet.gov/expapi/verbs/scored`	Achieved a score
experienced	`http://adlnet.gov/expapi/verbs/experienced`	General activity engagement
answered	`http://adlnet.gov/expapi/verbs/answered`	Responded to a quiz or question
attempted	`http://adlnet.gov/expapi/verbs/attempted`	Started an activity without completing it
progressed	`http://adlnet.gov/expapi/verbs/progressed`	Advanced within an activity
mastered	`http://adlnet.gov/expapi/verbs/mastered`	Demonstrated proficiency
interacted	`http://adlnet.gov/expapi/verbs/interacted`	General interaction with an object
launched	`http://adlnet.gov/expapi/verbs/launched`	Started an application or activity
bookmarked	`http://id.tincanapi.com/verb/bookmarked`	Saved something for later

Bring your own vocabulary

When an existing ADL, SCORM, or TinCan verb matches your semantics, prefer it — shared vocabulary makes cross-tenant analytics sharper. When nothing captures the meaning, mint a verb under a namespace you control, for example https://your-app.example/verbs/refactored, and start emitting it. No platform change is required and nothing needs approval before your data flows. New verbs that prove broadly useful get promoted into the canonical registry and documented; until then they work exactly the same.

Next: Concepts · API reference · Quickstart