Implementation layer

The question this layer answers

What is it built from?

The implementation layer is where technology commitments live, and the only place they live. The logical layer said what blocks exist; this layer says what each one is made of: software, hardware, or the user interface that people touch. Each element here realises something in the logical design.

Namespace: memo::architecture::implementation · Source: src/architecture/implementation/

Key elements

Software. IEC 62304 calls any identifiable part of a program a software item, and it decomposes software item by item. MEMO's base for that concept is SoftwareElement. It is named so because SysML reserves item for things that flow, which is what MEMO's DataItem is: software data or content that is stored or exchanged. Software is described in two views:

• The module view (IEC 62304 5.3 to 5.4): SoftwareSystem is the top, and SoftwareModules are the code units with design responsibility. Algorithm, DataModel and ConfigurationArtifact describe what they contain. An SBOMEntry records a component in the software bill of materials.
• The runtime view: a SoftwareComponent is a runtime component, with its concurrency, scheduling, health monitoring and fault containment. Its runtimeKind says what kind: a process, thread, task, service, container, partition, data store, or message broker.

Hardware. PhysicalElement is the root of a physical taxonomy: PhysicalAssembly and PhysicalSubassembly, HardwareAssembly, PhysicalComponent and HardwareComponent. Below them are electrical and electronic parts (PowerSupply, Battery, Cable, NetworkMedium), fluidic and pneumatic parts, mechanical parts and enclosures, optical, acoustic and thermal components, and the Sensors and Actuators that meet the physical world.

User interface. A UserInterface is what the user operates. A UIElement is one element of it, such as a banner or a button. A UIElement is a software element. A UIAction is an operative action, because clicking a button has a trigger, a precondition, a criticality and a potential harm, just as turning a knob does. UIState and UIEvent describe the interface's behaviour. An InteractionFlow is a reusable dialogue structure through the interface; one path through it is an OperativeScenario of kind ui. ScreenCapture and RegionBounds tie the model to real screen layouts.

How it connects

Within the layer. A UI element triggers a UI action (ElementTriggersAction). A screen capture shows a UI element (CapturesScreen). A SOUP item (IEC 62304's software of unknown provenance) is a SOUPSoftwareModule; an OTSSoftwareModule is the off-the-shelf kind of SOUP and adds the license, package URL and checksum. Any element can depend on a SOUP software element (DependsOnSoup).

To other layers and disciplines:

• It realises the logical design. An implementation element is linked to the logical element it realises with #refinement dependency, written as <realizing> to <realized>. See Logical.
• UI actions carry out functions: a UIAction performs a function. See Functional.
• Interaction serves use: an interaction flow serves a use case (FlowServesUseCase), and the interface supports operational tasks with a native dependency. See Operational.
• It is where controls are built. A risk control is implemented by an implementation element (ControlImplementedBy), and a use error happens at an element (ErrorAtElement). See Safety and risk and Human factors.
• It is deployed in the realization layer. Modules build into deployment units (BuildsInto), runtime components bind to memory (MemoryBinding), and exchanges bind to a network medium (ConnectionBinding). See Realization.

In the running example

The bedside display carries the alarm banner. The banner triggers the acknowledge action, which performs the detection function. A native dependency records that the display supports the nurse's acknowledgement task.

part uiBedside : UserInterface {
    @MemoIdentity { :>> providedId = "TA-UI-001"; :>> label = "BedsideDisplay"; }
    attribute :>> modality = "visual + audible";
}
part elAlarmBanner : UIElement {
    @MemoIdentity { :>> providedId = "TA-EL-001"; :>> label = "TempAlarmBanner"; }
    attribute :>> alarmPriority = NotificationPriorityKind::high;
    attribute :>> annunciationModality = "flashing banner + tone";
    attribute :>> silenceable = true;
}
action uiaAcknowledge : UIAction {
    @MemoIdentity { :>> providedId = "TA-UIA-001"; :>> label = "AcknowledgeAlarm"; }
    attribute :>> intent = InteractionIntentKind::acknowledgement;
    attribute :>> confirmationRequired = true;
    perform fnDetectDeviation;
}
connection : ElementTriggersAction connect element ::> elAlarmBanner to triggeredAction ::> uiaAcknowledge;
// Was `Supports`, a zero-attribute duplicate of both `Enables` and the
// native `dependency`.
dependency from uiBedside to actAcknowledgeAlarm::taskAckAlarm;

The full inventory

Generated from src/architecture/implementation/.

Elements

Hardware

Element	SysML kind	What it is
PhysicalElement (abstract)	part def	Physical element definition specializing MemoPart.
PhysicalAssembly	part def	Physical assembly definition specializing PhysicalElement.
PhysicalSubassembly	part def	Physical subassembly definition specializing PhysicalAssembly.
HardwareAssembly	part def	Hardware assembly definition specializing PhysicalAssembly.
PhysicalComponent	part def	Physical component definition specializing PhysicalElement.
HardwareComponent	part def	Hardware component definition specializing PhysicalComponent.
AcousticComponent	part def	Acoustic component definition specializing PhysicalComponent.
ThermalComponent	part def	Thermal component definition specializing PhysicalComponent.
ElectricalComponent	part def	Electrical component definition specializing PhysicalComponent.
ElectronicComponent	part def	Electronic component definition specializing PhysicalComponent.
PowerSupply	part def	Power supply definition specializing ElectricalComponent.
Battery	part def	Battery definition specializing ElectricalComponent.
Cable	part def	Cable definition specializing PhysicalComponent.
PhysicalConnectorPart	part def	Physical connector part definition specializing PhysicalComponent.
NetworkMedium	part def	Network medium definition specializing PhysicalComponent.
FluidicComponent	part def	Fluidic component definition specializing PhysicalComponent.
PneumaticComponent	part def	Pneumatic component definition specializing PhysicalComponent.
MechanicalPart	part def	Mechanical part definition specializing PhysicalComponent.
Enclosure	part def	Enclosure definition specializing MechanicalPart.
OpticalComponent	part def	Optical component definition specializing PhysicalComponent.
Sensor	part def	Sensor definition specializing PhysicalComponent.
Actuator	part def	Actuator definition specializing PhysicalComponent.

Software

Element	SysML kind	What it is
SoftwareComponent	part def	Software component definition specializing SoftwareElement.
OTSSoftwareComponent	part def	A runtime service or process that exists only because an OTS module is deployed. Optional: a library the product links normally needs only the module.
SoftwareElement (abstract)	part def	Software element definition specializing MemoPart.
SoftwareSystem	part def	Software system definition specializing SoftwareElement.
SoftwareModule	part def	Software module definition specializing SoftwareElement.
Algorithm	part def	Algorithm definition specializing MemoPart.
DataModel	part def	Data model definition specializing MemoPart.
ConfigurationArtifact	part def	Configuration artifact definition specializing MemoPart.
DataItem (abstract)	item def	Data item definition specializing MemoItem.
SOUPSoftwareModule	part def	Soupsoftware module definition specializing SoftwareModule.
OTSSoftwareModule	part def	Otssoftware module definition specializing SOUPSoftwareModule.
SBOMEntry	part def	An SBOM is a document; its entries are inventory records. An entry names one software element and says what is known about it as shipped. Vulnerabilities, anomalies and risks are separate objects that point at the entry; they are not attributes of the document.
SoftwareBillOfMaterials	part def	Software bill of materials definition specializing MemoPart.

Ui

Element	SysML kind	What it is
RegionBounds	attribute def	Region bounds definition.
UserInterface	part def	User interface definition specializing MemoPart.
UIElement	part def	Uielement definition specializing SoftwareElement.
OperatorInterfaceElement	part def	Operator interface element definition specializing PhysicalComponent.
ScreenCapture	part def	Screen capture definition specializing MemoEvidence.
UIState	part def	UI state is presentation state — distinct from system/device state.
UIEvent	part def	Uievent definition specializing MemoPart.
UIAction	action def	Clicking a button IS an operative action: it has a trigger, a precondition, a criticality, a potential harm and a frequency of use, exactly as turning a knob does.…
InteractionFlow	action def	A reusable dialogue structure through the UI; a selected path through it is a OperativeScenario with scenarioKind ui.

Connections at a glance

Each arrow is one relationship, from its source end to its target end. A grey box belongs to another layer.

flowchart LR
  MemoPart["MemoPart"]:::other
  SoftwareElement["SoftwareElement"]
  ScreenCapture["ScreenCapture"]
  UIElement["UIElement"]
  UIAction["UIAction"]
  InteractionFlow["InteractionFlow"]
  UseCase["UseCase"]:::other
  UseError["UseError"]:::other
  RiskControlMeasure["RiskControlMeasure"]:::other
  anyElement["any element"]:::other
  SoftwareModule["SoftwareModule"]
  SoftwareDeploymentUnit["SoftwareDeploymentUnit"]:::other
  SoftwareComponent["SoftwareComponent"]
  MemoryDevice["MemoryDevice"]:::other
  MemoInterface["MemoInterface"]:::other
  PhysicalComponent["PhysicalComponent"]
  Vulnerability["Vulnerability"]:::other
  SBOMEntry["SBOMEntry"]
  PostmarketProcess["PostmarketProcess"]:::other
  MemoPart -->|DependsOnSoup| SoftwareElement
  ScreenCapture -->|CapturesScreen| UIElement
  UIElement -->|NavigatesTo| UIElement
  MemoPart -->|ElementTriggersAction| UIAction
  InteractionFlow -->|FlowServesUseCase| UseCase
  UseError -->|ErrorAtElement| MemoPart
  RiskControlMeasure -->|ControlImplementedBy| anyElement
  SoftwareModule -->|BuildsInto| SoftwareDeploymentUnit
  SoftwareComponent -->|MemoryBinding| MemoryDevice
  MemoInterface -->|ConnectionBinding| PhysicalComponent
  Vulnerability -->|AffectsSBOMEntry| SBOMEntry
  PostmarketProcess -->|MonitorsSBOMEntry| SBOMEntry
  classDef other fill:#eef1f4,stroke:#9aa7b2,color:#4a5a66

Relationships declared here

Relationship	From	To	What it says
DependsOnSoup	MemoPart	SoftwareElement	Typed relationship from MemoPart to SoftwareElement.
CapturesScreen	ScreenCapture	UIElement	Which modelled screen an image is a rendering of.
NavigatesTo	UIElement	UIElement	Typed relationship from UIElement to UIElement.
ElementTriggersAction	MemoPart	UIAction	Typed relationship from MemoPart to UIAction.
FlowServesUseCase	InteractionFlow	UseCase	Typed relationship from InteractionFlow to UseCase.
ErrorAtElement	UseError	MemoPart	Typed relationship from UseError to MemoPart.
ControlImplementedBy	RiskControlMeasure	any element	A risk control implemented by a UI element or by task design (confirmation dialog, lockout, guarded control).

Relationships from elsewhere that reach this layer

Relationship	Declared in	From	To	What it says
BuildsInto	realization	SoftwareModule	SoftwareDeploymentUnit	Typed relationship from SoftwareModule to SoftwareDeploymentUnit.
MemoryBinding	realization	SoftwareComponent	MemoryDevice	AADL actual_memory_binding. Which memory a software component's code and data occupy — what makes a memory budget a claim about a device rather than a string.
ConnectionBinding	realization	MemoInterface	PhysicalComponent	AADL actual_connection_binding. Which physical thing carries an interface: a network medium under a component exchange, a cable or harness under a hardware Interface, a connector, a tube.…
AffectsSBOMEntry	cybersecurity	Vulnerability	SBOMEntry	Typed relationship from Vulnerability to SBOMEntry.
MonitorsSBOMEntry	cybersecurity	PostmarketProcess	SBOMEntry	Typed relationship from PostmarketProcess to SBOMEntry.

Enumerations

Enumeration	Values
RuntimeKind	process, thread, task, service, container, partition, dataStore, messageBroker
ModuleKind	unit, code, firmware
SbomFormatKind	spdx, cycloneDx, other
UIElementFormKind	screen, dialog, panel, menu, tab, drawer, wizardStep, button, field, selector, slider, table, chart, icon, textMessage, decoration
UIDisclosureKind	inline, overlay, transient, scrolled, conditional
BoundsDetectionKind	manual, automatic, automaticConfirmed, imported
InteractionIntentKind	userInput, feedback, navigation, confirmation, inputValidation, errorMessage, alarmAnnunciation, acknowledgement, cancellation, timeout, lockout, correction, recovery
OperatorInterfaceFormKind	knob, dial, pushButton, toggleSwitch, rockerSwitch, lever, physicalSlider, keypad, footPedal, touchSurface, indicatorLamp, gauge, audibleIndicator, hapticIndicator, printedMarking

Go deeper

• The GPCA infusion pump: requirements and architecture.
• The implementation API.