flowchart TB N1["xAPI Statement Resource
POST /xapi/statements"]:::t1 N2["Ingestion Gateway
Structural Validation"]:::t1 N3["Durable Event Queue
At-Least-Once Delivery"]:::t1 N4["Stream Processor
Semantic Validation, Schema On Read"]:::t2 N5["Event Store
immutable statement log (Ch. 5)"]:::t3 N6["Compression Pipeline
Change-Driven Materialization"]:::t3 N7["Summary Vertex
Absolute Value Write"]:::t3 N1 --> N2 --> N3 --> N4 --> N5 --> N6 --> N7 classDef t1 fill:#0f5c53,stroke:#0a3f39,color:#fff,font-size:14px classDef t2 fill:#2a9d8f,stroke:#1f7a6f,color:#fff,font-size:14px classDef t3 fill:#8fd3c9,stroke:#3bab9d,color:#0c2f2b,font-size:14px linkStyle default stroke:#999,stroke-width:2px