Relationships

Relationships make the model navigable and testable. The reasoning: a model element on its own is a note; a typed relationship is a claim a reviewer can challenge. Select the narrowest relationship whose meaning and endpoint direction match what you are asserting.

Relationship families

MEMO defines typed relationships across operational, architecture, assurance, and product domains. The chart shows representative pairs in the direction declared by the ontology:

High-value traceability links

Most links between architecture layers are native SysML v2. MEMO adds its own typed relationship only where the native form would lose meaning a medical-device argument needs. Each layer page of the ontology lists every relationship that touches it, generated from the source.

Write	From	To	Use it to say…
actor (native)	User	UseCase	This user pursues the goal
Motivates	Need	UseCase	This need is why the goal exists
RealizesUseCase	OperationalWorkflow	UseCase	This organised work realises the goal
perform (native)	Action or UI action	Function or scenario	This action carries out that behaviour
allocate (native)	Function	Component	This component is responsible for this behaviour
#refinement dependency (native)	Realizing element	Realized element	This implementation realises that design element
allocation … : BuildsInto / : DeploysTo / : HostedBy	Module / unit / node	Unit / node / board	The deployment chain
DerivesFrom	Need, risk, threat, or other driver	Requirement	This requirement exists because of this driver
satisfy (native)	Requirement	Design element	This design element satisfies the obligation
Mitigates	Risk control	Hazard or vulnerability	This control reduces this risk item (mitigationKind)
ControlImplementedBy	Risk control	Design element	This element implements the control
CommitsUseError / Causes	Task / use error	Use error / hazard	The use-related risk path
subject (native) / Validates	Verification case / claim, use case, or task	What it checks / validation case	This case checks the claim
ProducesEvidence	Verification or validation case	Evidence	This activity produced this evidence

The ontology includes more specialized links for cybersecurity, FMEA, fault trees, lifecycle change, interaction, and document views. Each is a connection def, or an allocation def for the deployment chain, specializing MemoRelationship with typed ends, so the full inventory is discoverable in src/core/relationships and each domain package.

Before you reach for a new connection def, check that SysML v2 does not already supply the construct: many relationships (flow, bind, actor, succession, nesting) are native, and a reinvented edge suppresses the checking the native one performs. See Naming and native constructs for the corpus-first rule, the native-construct lookup table, and the allocation … : DeploysTo allocate … extension pattern.

Direction matters

Write the relationship so its endpoint roles read as a sentence:

connection : Mitigates
    connect control ::> rcReAnnunciate
    to mitigatedElement ::> hzUndetectedDeviation;

This reads: “rcReAnnunciate mitigates hzUndetectedDeviation.” A connection binds its ends by position, so the source end comes first.

Typed references

Where an element holds a reference—a flow's start function, an exchange's endpoints, an instance's definition—MEMO uses typed refs. The tool resolves the reference, and the conformance rules (rules/ontology) can check it. Path-like labels (sourcePortPath) serve as descriptive annotations for external tool round-trips.

Prefer semantic links over generic traces

A generic trace only says two records are related. A semantic relationship says how they are related and enables stronger validation. Use a generic trace only when no stable, more precise relationship exists, and record the rationale.