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Verb IRI Anatomy

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Learning Objective

Decompose a verb IRI into its three parts (scheme + namespace + local name), and recognize valid versus invalid verb IRIs at a glance.

  • Bloom Level: Understand
  • Bloom Verb: Decompose / Identify
  • Library: p5.js

Description

Every xAPI verb is identified by an IRI — an Internationalized Resource Identifier. To the eye, the IRI looks like a single string; to xAPI, it has internal structure. Understanding that structure is the difference between debugging "why does my custom verb collide with the ADL one?" in five minutes versus five hours.

This sim shows the three parts of a verb IRI:

  • Scheme (blue) — the protocol, almost always http:// or https://
  • Namespace (green) — the publisher's path: e.g. adlnet.gov/expapi/verbs/
  • Local name (orange) — the verb itself: passed, experienced, etc.

Hover any colored part to see what it means in the info panel. Click to lock the selection. Use the buttons to swap in a TinCan verb or a custom verb and see how each follows the same three-part pattern.

Toggle "Show invalid examples" to see common mistakes — a bare local name without a scheme, a custom URI scheme like myapp:, or an IRI with spaces — and read why each is rejected.

Lesson Plan

Suggested length: 5–8 minutes.

  1. Identify the parts (2 min). Default IRI is the canonical passed verb. Hover each colored part. Notice that the same English word "passed" only matters because of the namespace it lives under.
  2. Compare publishers (2 min). Click TinCan, then Custom. Same shape; different namespace. The verb identity is the whole IRI, not the local name.
  3. Spot the failures (2 min). Toggle invalid examples. Predict why each is rejected before reading the explanation.
  4. Discussion (1–2 min). Why does xAPI require IRIs instead of plain strings like SCORM did? Why does the namespace matter even though most IRIs never resolve to a live page?

Try This

  • Two textbooks define a verb at http://example.com/verbs/passed. Same IRI, same namespace, same local name. Are these the same verb? (Yes — IRI equality is the definition.)
  • Your team registers a custom verb at https://corp.example/verbs/explored and another at http://corp.example/verbs/explored. Are these the same verb? (No — http:// and https:// differ in the scheme.)
  • Why does ADL's namespace not include a port number, language tag, or query string? What would change about IRI comparison if it did?

References

  • xAPI 2.0 Specification, §4.1.4.1 Verb
  • RFC 3987 Internationalized Resource Identifiers (IRIs)