Four connected layers
interface: Screens, interactions, accessibility, and the feedback that helps someone finish a real task. Hands a clear user intent to the workflow layer.
workflow: Business rules, integrations, and AI steps with explicit boundaries, review points, and recovery paths. Coordinates actions against the data layer.
data: The information model, permissions, and history that keep the product consistent as work moves through it. Depends on infrastructure for durable storage and access.
infrastructure: Deployment, monitoring, recovery, and the operating routines that make a system understandable after release. Supports every layer with observable, repeatable operation.