flowchart TB
  subgraph S["xAPI Statement"]
    A["Actor<br/>(Agent/Group)"]
    V["Verb<br/>(URI + display)"]
    O["Object<br/>(Activity/Agent/StatementRef)"]
    R["Result<br/>(success, score, duration, response*)"]
    C["Context<br/>(activity context, group, platform, instructor*, contextActivities, registration, extensions)"]
    T["Timestamp<br/>(event time)"]
    X["Extensions<br/>(custom fields in allowed locations)"]
  end

  A --> V --> O
  O --> R
  O --> C
  O --> T
  R -. "optional" .-> X
  C -. "optional" .-> X