System architecture model

System Coordination Framework (SC1–SC8)

An original system architecture model in eight elements, SC1–SC8, for how software, control, communication, motion, safety, diagnostics, people and models coordinate.

By Saina Veigel

Eight elements of system coordination

Each element describes one layer of how a technical system coordinates itself. Together they form one architecture: logic, execution, communication and dynamics, bounded by protection, observed by diagnostics, operated by people and mirrored in models.

SC1 — Computing & Software ArchitectureThe logical intelligence layer
SC2 — Control System IntegrationThe physical control layer
SC3 — Communication Logic & ProtocolsThe interaction layer between systems
SC4 — Motion & Process CoordinationThe dynamic behavior layer
SC5 — Safety & Authorization CoordinationThe protection layer
SC6 — Diagnostics, Monitoring & System HealthThe awareness layer
SC7 — Human–Machine InteractionThe interaction layer with people
SC8 — System Modeling & Digital TwinThe virtualization layer

SC1 — Computing & Software Architecture

The logical intelligence layer

SC1 describes how a system thinks before it acts. It captures the modes a system can be in, the rules that allow or forbid a change of mode, and the order and timing in which software work is carried out. In SC1, coordination is a property of the logic itself: a sequence is only well coordinated when every state is named, every transition has a condition and every constraint is expressed as a rule the software can evaluate.

SC1 is deliberately independent of the hardware it will later run on. It treats timing and determinism as design decisions rather than accidents of the platform, and it allows protective boundaries to exist as logic — soft limits and virtual zones — so that behavior can be constrained before a physical barrier is ever reached. This makes SC1 the place where the intent of the whole system is written down in executable form.

Multi-layer approach

SC1 defines the logical intelligence layer of a system. It models how software components coordinate, sequence, and constrain machine behavior.

1State Layeroperational modes, transitions
2Logic Layerinterlocks, conditions, constraints
3Execution Layerscheduling, priorities, timing
4Virtual Safety Layersoft limits, virtual fences

System coordination role

SC1 provides the internal logic that interacts with SC2 (control hardware) and SC3 (communication). It is the “brain” of coordination.

Interfaces withSC2 SC3

Scope

In scope

State machines
Scheduling and task models
Real-time operating systems
Logical control models
Software interlocks
Virtual safety zones
Soft Controls (logical layer)
Execution timing and determinism
Software-based coordination logic

Out of scope

Physical control hardware
Fieldbus wiring
PLC hardware architecture
Mechanical safety devices

SC2 — Control System Integration

The physical control layer · PLC / SPS / SSPS / IPC

SC2 is where coordination becomes tangible. It describes how control devices, their inputs and outputs and their protective hardware are assembled into one controlling body that executes in fixed, repeatable cycles. The question SC2 answers is not what the system should do, but how reliably and within which physical limits it is able to do it, cycle after cycle.

SC2 treats the mapping between logical signals and physical terminals as a first-class architectural decision, because every coordination rule from SC1 ultimately depends on a signal arriving at the right place at the right time. Protective hardware is modeled here as a layer of its own, so that physical constraints remain effective even when the logic above them is wrong or absent.

Multi-layer approach

SC2 defines the physical control layer.

1Hardware LayerPLC, SSPS, IPC
2I/O Layersensors, actuators, wiring
3Safety Layerrelays, contactors, hard stops
4Execution Layerscan cycles, deterministic loops

System coordination role

SC2 is the execution substrate for SC1 logic. It enforces physical constraints and executes commands from SC1.

Interfaces withSC1 SC3 SC5

Scope

In scope

PLC/SPS/SSPS architectures
IPC integration
Hard Controls (physical layer)
Safety hardware
Fieldbus systems
I/O mapping
Deterministic execution cycles

Out of scope

High-level software logic
HMI/UX design
Network routing
Mechanical actuation design

SC3 — Communication Logic & Protocols

The interaction layer between systems

SC3 describes how independent systems come to share one understanding of the situation. Messages are only one part of it: SC3 is concerned with whether a state change reaches every party that depends on it, whether all parties agree on when it happened, and whether the absence of a message is itself noticed and acted upon.

In SC3, communication is designed as coordination logic rather than as plumbing. Liveness signals, synchronized clocks and explicit state propagation turn a set of connected machines into a system whose behavior can be predicted as a whole. SC3 therefore favors deterministic, time-bounded exchange and treats unbounded, best-effort messaging as outside the coordination core.

Multi-layer approach

SC3 defines the interaction layer between systems.

1Transport Layerfieldbus, Ethernet
2Protocol LayerOPC UA, MQTT
3Coordination Layerstate sync, heartbeat
4Timing Layerdeterministic timing, PTP

System coordination role

SC3 is the glue between SC1 and SC2 across distributed systems. It ensures synchronized, safe, and predictable multi-system behavior.

Interfaces withSC1 SC2 SC4 SC5

Scope

In scope

OPC UA
MQTT
Deterministic communication
Heartbeat mechanisms
Synchronization
State propagation
Time synchronization (NTP/PTP)
Coordination messaging

Out of scope

Physical wiring
PLC hardware
High-level business networks
Non-deterministic cloud messaging

SC4 — Motion & Process Coordination

The dynamic behavior layer

SC4 describes how movement and process steps are orchestrated over time. Where SC1 decides which step is allowed, SC4 decides how the step unfolds: along which path, at which speed, in which relation to other axes, machines and robots, and at which moment the next step may begin.

SC4 views a production line as a choreography rather than a collection of independent movements. Its central concern is the transition — the handover from one step, one axis or one machine to the next — because that is where timing errors, collisions and lost throughput originate. SC4 relies on SC1 for the rules, on SC2 for execution and on SC3 for synchronization, and it always operates inside the boundaries set by SC5.

Multi-layer approach

SC4 defines the dynamic behavior layer.

1Motion Layertrajectories, limits
2Process Layersteps, transitions
3Synchronization Layermulti-axis coordination
4Interaction Layerrobot ↔ machine coordination

System coordination role

SC4 is the behavioral engine of the system. It orchestrates motion, processes, and transitions across machines.

Interfaces withSC1 SC2 SC3 SC5

Scope

In scope

Motion control
Axis synchronization
Process sequencing
Transition logic
Multi-machine coordination
Robot coordination
Process timing models

Out of scope

Mechanical design
PLC hardware
Safety risk assessment
HMI design

SC5 — Safety & Authorization Coordination

The protection layer · ISO 12100-aligned

SC5 describes how protection is coordinated across a system rather than attached to individual machines. It links the understanding of what can go wrong with the functions that respond to it, and with the question of who is permitted to do what, in which mode, at which moment. Authorization is treated as part of safety coordination, because an action that is safe for one role or mode can be hazardous in another.

The distinctive concern of SC5 is propagation. A stop, a change of safety state or a withdrawn permission is only effective when every affected part of a distributed system reaches the intended state in the intended order. SC5 follows the logic of hazard identification and risk reduction associated with ISO 12100, but it is an architectural view: it neither replaces a risk assessment nor states that any design conforms to a standard.

Multi-layer approach

SC5 defines the protection layer.

1Hazard Layeridentification, classification
2Risk Layerevaluation, reduction
3Safety Function LayerSTO, SS1, SLS, etc.
4Coordination Layerpropagation, transitions

System coordination role

SC5 ensures that SC1–SC4 operate within safe boundaries and that safety states propagate correctly across distributed systems.

Interfaces withSC1 SC2 SC3 SC4

Scope

In scope

Hazard types
Risk assessment
Safety functions
Authorization logic
Emergency stop propagation
Soft stop / hard stop
Safe torque off / safe stop
Safety state machines

Out of scope

Mechanical guard design
Electrical installation standards
Non-functional safety documentation

SC6 — Diagnostics, Monitoring & System Health

The awareness layer

SC6 describes how a system knows its own condition. It turns raw observations into judgments — normal, degrading, faulty — and makes those judgments available to the rest of the architecture in time to matter. A system without SC6 can still act, but it cannot tell whether it is still able to act as intended.

SC6 pays particular attention to how faults travel. A single deviation can surface as many symptoms in many places; SC6 models the path from cause to consequence so that the system reports the origin, not only the noise. It is kept apart from protective functions on purpose: SC6 informs, anticipates and records, while the obligation to protect remains with SC5.

Multi-layer approach

SC6 defines the awareness layer.

1Sensor Layerdata acquisition
2Analysis Layerthresholds, models
3Prediction Layerdegradation, trends
4Reporting Layeralarms, logs

System coordination role

SC6 provides the system’s self-awareness, enabling SC1–SC5 to adapt to faults, degradation, or anomalies.

Interfaces withSC1 SC2 SC3 SC4 SC5

Scope

In scope

Fault detection
Condition monitoring
Predictive maintenance
Telemetry
Logging
Health models
Error propagation

Out of scope

Safety functions
Motion control
PLC hardware design

SC7 — Human–Machine Interaction

The interaction layer with people · HMI & UX

SC7 describes how human intent enters the system and how the system’s state returns to people in a form they can act on. It starts from roles — who is at the machine, with which task and which permissions — and derives screens, controls and feedback from those roles rather than from the structure of the underlying software.

In SC7, an interface is part of the coordination chain, not a layer painted on top of it. A command given at the wrong moment, a status shown ambiguously or an alarm lost among many can undo the coordination achieved in SC1–SC5. SC7 therefore treats safe interaction patterns — confirmation, clear state indication, role-appropriate access — as architectural elements in their own right.

Multi-layer approach

SC7 defines the interaction layer.

1Role Layeroperator, maintenance, admin
2Interface Layerscreens, controls
3Interaction Layercommands, feedback
4Safety Layersafe interaction patterns

System coordination role

SC7 connects human intent to SC1–SC5 logic, ensuring safe, ergonomic, and predictable interaction.

Interfaces withSC1 SC5 SC6

Scope

In scope

HMI design
UX models
Operator roles
Soft Controls (HMI layer)
Visualization
Interaction safety

Out of scope

PLC hardware
Motion control
Network protocols

SC8 — System Modeling & Digital Twin

The virtualization layer

SC8 describes the system as a model that can be run, questioned and corrected before and alongside the real one. It brings the logic of SC1, the timing of SC2 and SC3, the dynamics of SC4, the protective behavior of SC5, the health signals of SC6 and the interaction of SC7 into one virtual environment, where their interplay can be observed without risk to people or equipment.

SC8 does not end at commissioning. A model that stays synchronized with the running system becomes a second view of it — a place to test a change, replay an incident or evaluate a safety scenario that must never be staged on the real machine. The architectural value of SC8 lies in this continuity: the same model accompanies the system from its first design to its last modification.

Multi-layer approach

SC8 defines the virtualization layer.

1Model Layerkinematics, logic, processes
2Simulation Layervirtual execution
3Validation Layersafety, timing, behavior
4Synchronization Layerdigital ↔ physical

System coordination role

SC8 enables SC1–SC7 to be tested, validated, and optimized in virtual environments before deployment.

Interfaces withSC1 SC2 SC3 SC4 SC5 SC6 SC7

Scope

In scope

Simulation
Virtual commissioning
Digital process models
Virtual safety tests
Twin synchronization
Model-based coordination

Out of scope

Physical installation
PLC wiring
Mechanical CAD

How to cite

Saina Veigel (2026). System Coordination Framework (SC1–SC8). AI TechDoc Blog. https://knowledge.aitechdoc.world/system-coordination-framework

About this framework

The System Coordination Framework is an independent work. The glossaries of AI TechDoc Blog are separate works: each element only lists glossary entries as references, and the framework neither reproduces nor restates their definitions.

The framework contains no normative text from IEC, ISO or other standards. Naming a standard or a concept does not mean that a system conforms to it, and the framework does not replace a risk assessment or the instructions for use of a machine.