ISA95Reference is a concept that represents a relationship between modelling targets and is represented by UML Association and by OPC UA ReferenceType (see Table 6).

Table 6– Transformation rule of a ISA95Reference

5.1.7.2 UMLAssociation

UMLAssociation represents an association between elements of a class and elements of another or the same class. The UMLAssociation is transformed to subtypes of OPC UA NonHierarchicalReferences (see Table 7).

Table 7– Transformation rule of the elements of UMLAssociation

ISA-95	OPC UA	Description
UMLAssociation	ReferenceType	ISA95Reference is defined by ReferenceType. Name of the association may be a name of ReferenceType, and cardinality of the association may be mapped into a Modelling Ruleof target Nodeof the Reference.

ISA-95	OPC UA	Description
UMLRole	SourceNode, TargetNode	UMLRole may be transformed into the restrictions of ReferenceType.
UMLCardinality	N/A	Standard ModellingRulesonly affect instance declaration specified by subtypes of Hierarchical References.
UMLAssociation Name	BrowseName	A name defined in ISA-95 may be changed. InverseName will be defined.

Instance Nodesthat are referenced by NonHierarchicalReferencesare not instantiated when an instance of an ObjectType or VariableType is created.

UMLGeneralization is used to describe that an element of UMLClass is a specialized type of the super UML Class, it mapped to the OPC UA HasSubtype ReferenceType.

UMLDependence is a weak association that is used to describe a modelling element that depends on another modelling element. This standard doesn’t support this concept in general terms. Depending on the nature of the dependence it may be modelled as a custom reference.

UMLAggregation is used to describe that an element of the class is made up of elements of other classes; it is mapped tosubtypes of the OPC UA Aggregates ReferenceType (see Table 8).

Table 8– Transformation rule of the elements of UMLAggregation

ISA-95	OPC UA	Description
UMLRole	SourceNode, TargetNode	UMLRole may be transformed into the restrictions of ReferenceType.
UMLCardinality	N/A	Standard ModellingRules onlyaffect instance declaration specified by sub-types of Hierarchical References.
UMLAssociation Name	BrowseName	A name defined in ISA-95 may be changed. InverseName will be defined.

UMLComposite is used to describe a strong form of aggregation, it is mapped to OPC UA HasComponentor subtypes of OPC UAHasComponent ReferenceType(see Table 9).

Table 9– Transformation rule of the elements of UMLComposite

ISA-95	OPC UA	Description
UMLRole	SourceNode, TargetNode	UMLRole may be transformed into the restrictions of ReferenceType.
UMLCardinality	ModellingRule	1	Mandatory
		0..1	Optional
		0..N	OptionalPlaceholder
		1..N	MandatoryPlaceholder
UMLAssociation Name	BrowseName	A name defined in ISA-95 may be changed. InverseName will be defined.