A layered architecture from business intent to physical action.

1. Application Layer

Applications express operational intent. They may discover that a dryer supports timed cycles up to 120 minutes, but they should not know its output channel, pulse sequence or UART frame.

• Self-service POS and customer applications
• Operator and administration dashboards
• Payment orchestration and partner integrations
• Analytics and reporting applications

2. SDL Control Plane

The control plane manages shared representation and coordination. It may run in the cloud, on-premises or locally, and it is not tied to one vendor implementation.

3. SDL Edge Runtime

The edge is the boundary between remote software and physical operations. It keeps critical logic near the machines and is the most important component of the reference architecture.

• Local asset and device state
• Command validation, expiration and idempotency
• Safety rules and physical confirmation
• Offline event persistence and later synchronization
• Adapter supervision and diagnostics
• Local API for trusted site applications

4. Device Adapter Layer

An adapter translates a standard SDL operation into the correct hardware behavior. Register addresses, serial settings, GPIO polarity and pulse timing belong here.

SDL command
  start_cycle(machine.w1)

Adapter mapping
  device: modbus-board-01
  output: channel 1
  pulse: 30 ms
  confirmation: input channel 1

5. Physical Infrastructure

SDL does not require equipment to be natively “smart.” Legacy machines can participate through adapters, while newer machines may expose richer digital capabilities.

Asset and device are different

An asset is the stable object an application uses, such as Washer W1. A device is the technical component that controls or reports it, such as an eight-channel Modbus board.

Replacing the board changes the mapping, not the asset identity, payment history or user interface.

Command flow

1. POS submits start_cycle for machine.d2
2. Control plane routes the command to its site
3. Edge validates target, expiration and local policy
4. Adapter performs the hardware-specific action
5. Edge observes the machine state
6. Events report acceptance, execution and confirmation
7. Applications update from observed state

Deployment models

What phase 1 intentionally leaves open

• Exact MQTT topic structure
• Final command and event JSON schemas
• Adapter process-isolation model
• Certification and conformance rules
• Final security credential profile

Those decisions belong to later technical specification phases and should be informed by implementation experience.