C4 model

standard

Simon Brown's four-level architecture-diagram model — the shape of a WAD's Systems view.

Context / Container / Component / Code, each level zooming into the last — see c4model.com. WAD adapts it: the context diagram is derived from relations rather than drawn, and the Code level is a typed code_item (module graph / DB schema / class diagram / API) that extractor scripts own, documenting the public interface only.