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References: The xAPI Statement Model — Actor, Verb, Object, Result, and Context

  1. JSON - Wikipedia - Reference for the data format every xAPI statement is built in, including type rules, escaping, and the conventions xAPI inherits. Essential background for reading and constructing statement payloads.

  2. Internationalized Resource Identifier - Wikipedia - Explains the IRI / IRI-reference syntax used for verb IDs, activity IDs, and extension keys. Clarifies why xAPI identifiers look URL-shaped but aren't required to resolve.

  3. ISO 8601 - Wikipedia - The timestamp format xAPI mandates for the timestamp and stored fields, including timezone offsets and fractional seconds. Critical for getting "when did this happen" right.

  4. RESTful Web APIs - Leonard Richardson, Mike Amundsen, Sam Ruby - O'Reilly Media - Foundational treatment of resource-oriented design, hypermedia, and JSON-based APIs that grounds the choices xAPI's statement endpoints inherit.

  5. Designing Data-Intensive Applications - Martin Kleppmann - O'Reilly Media - Chapter on event sourcing and immutable append-only logs explains exactly why xAPI statements are designed to be immutable once stored.

  6. xAPI Spec Part Two — Experience API - ADL Initiative - The authoritative section on statement structure, required and optional properties, data types, and equivalence rules. The reference this chapter is teaching readers how to read.

  7. xAPI Statements 101 - Rustici Software - Walks through actor / verb / object construction with annotated JSON examples and common-mistake warnings. Pairs perfectly with this chapter's field-by-field tour.

  8. TinCanJS Library - Rustici Software - The most-used JavaScript helper for constructing and validating xAPI statements; reading its source clarifies what the spec means in practice.

  9. ADL xAPI Lab - ADL Initiative - A live web tool that lets you build, send, and inspect xAPI statements against a hosted LRS sandbox. Hands-on companion to this chapter's worked examples.

  10. JSON Schema - JSON Schema Organization - The validation language used by community-maintained xAPI statement schemas; useful for adding statement validation in CI before statements ever reach an LRS.