The Webel Digital Twin Pattern for SysML policy notes

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Policy notes supporting the Webel Twin Pattern for SysML. For examples of their use, please visit:

TRAIL: A SysML Pattern for Digital Twinning

The following list is NOT ordered:

[POLICY]{STRICT} Webel Twin Pattern: A LogicalProcess may only act on a PhysicalEntity via a PhysicalProcess
[ASSERTION]{STRICT} Webel Twin Pattern: A DigitalEntity (a.k.a. «digital» @Entity) used as a digital variant must not be directly bound to a «physical» PhysicalEntity (may not directly actuate/sense/affect)
[CONVENTION]{SUBJECT-TO-CHANGE} Webel Twin Pattern: Convention: [MIGHT CHANGE]: A '*' prefix in a Property name of a «digital» @Block in a DigitalTwin model indicates a mapped block property, which must be typed by a non-digital «mappable» Block, and must have the «@» keyword applied.
[ASSERTION, POLICY]{STRICT} Webel Twin Pattern: A DigitalTwin (even a "process twin" or "finance twin"), always, without exception, BY DEFINITION HERE either directly or indirectly involves at least one existing or anticipated PhysicalEntity (even if only via another DigitalTwin)!
[POLICY]{STRICT} Webel Twin Pattern: The sensor/actuator twinning control loop can involve automated devices (SensorDevice and/or ActuatorDevice) and or humans (SensorHuman and/or ActuatorHuman).
[CONVENTION]{SUBJECT-TO-CHANGE} Webel: Convention: [MIGHT CHANGE]: An '@' prefix in a DigitalTwin model indicates a «digital» Block that maps a non-digital «mappable» Block.
[POLICY] Webel Twin Pattern: Once a PotentialPhysicalAsset has been integrated with a real, existing (has mass) ActualPhysicalAsset under twinning control, its job is done forever (although it may be kept as an historical tracking record).
[POLICY]{STRICT} Webel Twin Pattern: A «digital» DigitalEntity (a.k.a. @Entity) encapsulates strictly geometrical, spatial, and material aspects of a «physical» PhysicalEntity only. BY DEFINITION of this pattern it DOES NOT encapsulate processes!
[ASSERTION]{STRONG} Webel Twin Pattern: Not every twinnable PhysicalEntity is worth treating as an asset.
[POLICY]{STRICT} Webel Twin Pattern: A DigitalTwin must model processes and the entities they act on separately.
[ASSERTION]{STRONG} Webel Twin Pattern: An AssetSpecification may contain ANY information or data of ANY kind in ANY format about how to acquire, manifest, build, or create a physical asset. This information may be distributed across an @Entity and a PotentialPhysicalAsset.
[POLICY]{STRICT} Webel Twin Pattern: It is a DigitalEntity (a.k.a. @Entity) - not the DigitalTwin that owns it - that directly «replicates» geometrical, spatial, and material aspects (only) of a single PhysicalEntity.
[POLICY]{STRICT} Webel Twin Pattern: A DigitalTwin and PhysicalEntity must both be 'attached' to Sensors and/or Actuators under management of the DigitalTwin before the twinning control loop is fully entered.
[POLICY]{STRICT} Webel Twin Pattern: A DigitalTwin manages a control loop including a PhysicalEntity and a DigitalEntity (a.k.a. @Entity) that «replicates» it. It typically includes at least one Sensor and at least one Actuator.
[POLICY]{STRICT} Webel Twin Pattern: An ActualPhysicalAsset is an asset that is also a «physical» PhysicalEntity.
[POLICY]{STRICT} Webel Twin Pattern: A PotentialPhysicalAsset is «digital», not «physical». It is used to acquire (an existing) or create (build, manifest, make) an «physical» ActualPhysicalAsset, which is a special case of «physical» PhysicalEntity.
[POLICY]{STRONG} Webel Twin Pattern: The information and data in AssetSpecification leveraged for creation of a new ActualPhysicalAsset need not necessarily only be «digital».
[WARNING]{INFORMATIVE} WARNING: In natural language casual conversation one often hears people speaking of a digital twin "replicating" or "twinning" a physical entity. If you do it that way literally, you will NOT have anything to manage the control system loop!
[CONSTRAINT, POLICY]{STRICT} Webel Twin Pattern: DigitalTwin: The multiplicity of 'digitalEntity:@Entity' and 'physicalEntity:PhysicalEntity' MUST be [1] when the DigitalTwin is in the state Attached, the @Entity is in the state Bound, and the PhysicalEntity is in the state Exists.
[POLICY]{STRICT} Webel Twin Pattern: A «digital» DigitalEntity (a.k.a. @Entity) is NOT a representation! It is a digital encapsulation (it can only be perceived at the level of "bits and bytes"). It HAS many representations (such as views)!
[POLICY]{STRICT} Webel Twin Pattern: The primary aim of the digitalEntity:@Entity of a DigitalTwin is to replicate its physical:PhysicalEntity as closely as possible (not to explore variants).
[POLICY]{STRICT} Webel Twin Pattern: A DigitalTwin may use one or more variantEntity:@Entity[0..*] to explore the impact of changes (optimisation studies, trade off studies) and then use them to drive the PhysicalEntity into a desired state (via its ControlSystem).
[POLICY]{STRICT} Webel Twin Pattern: Communication between the ControlSystem of a DigitalTwin and its digitalEntity:@Entity is via a dedicated protocol (ReadTwin, WriteTwin) distinct from the sensor reading or actuator driving signals.

Notes

Relevant snippets (from other sources)

Visit also

Screencast: The Webel Digital Twin Pattern for SysML: Part 1: Simulating acquisition or creation of physical assets using Activities and StateMachines in Cameo Simulation Toolkit.

Webel's Best Practice policy notes for MBSE with SysML1.x (and UML) and the MagicDraw/Cameo tools

Visit also (backlinks)

Policy Notes for the Webel Parsing Analysis recipe for SysML

TRAIL: A SysML Pattern for Digital Twinning

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