The System Architecture Document provides a layered description of the system’s structure using the C4 model. It comprises a System Context Diagram (Level 1) showing the system within its broader environment, a Container Diagram (Level 2) showing the major technical building blocks within the system boundary, and Component Diagrams (Level 3) for sufficiently complex containers.

Each diagram serves a different audience. The Context and Container diagrams are appropriate for the AI Governance Lead, Legal and Regulatory Advisor, and notified body reviewers. Component and Sequence diagrams serve the Technical SME and engineering team. The document is structured in layers of increasing detail so that each reader can access the level appropriate to their role.

The architecture document must be version-controlled alongside the code and model artefacts. A diagram that shows the architecture as designed six months ago rather than the architecture as deployed today constitutes a non-conformity. Tooling that generates diagrams from code or infrastructure definitions (Structurizr for C4, Terraform graph for deployment diagrams) reduces the risk of documentation drift. The architecture document feeds into AISDP Module 3 and is a primary reference during the conformity assessment.

Key outputs

• System Context Diagram (C4 Level 1)
• Container Diagram (C4 Level 2)
• Component Diagrams (C4 Level 3) for complex containers
• Version-controlled architecture document as Module 3 evidence