Referencesare defined as instances of ReferenceType Nodes. ReferenceType Nodesare visible in the AddressSpaceand are defined using the ReferenceType NodeClassas specified in Table 9. In contrast, a Referenceis an inherent part of a Nodeand no NodeClassis used to represent References.

This standard defines a set of ReferenceTypesprovided as an inherent part of the OPC UAAddress Space Model. These ReferenceTypesare defined in Clause 7and their representation in the AddressSpaceis defined in OPC 10000-5. Serversmay also define ReferenceTypes. In addition, OPC 10000-4defines NodeManagement Servicesthat allow Clientsto add ReferenceTypesto the AddressSpace.

Table 9– ReferenceType NodeClass

Name

Use

Data Type

Description

Attributes

Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

IsAbstract

M

Boolean

A boolean Attributewith the following values:

TRUEit is an abstract ReferenceType, i.e. no Referenceof this type shall exist, only of its subtypes.

FALSEit is not an abstract ReferenceType, i.e. Referencesof this type can exist.

Symmetric

M

Boolean

A boolean Attributewith the following values:

TRUEthe meaning of the ReferenceTypeis the same as seen from both the SourceNodeand the TargetNode.

FALSEthe meaning of the ReferenceTypeas seen from the TargetNodeis the inverse of that as seen from the SourceNode.

InverseName

O

LocalizedText

The inverse name of the Reference, which is the meaning of the ReferenceTypeas seen from the TargetNode.

References

HasProperty

0..*

Used to identify the Properties (see 5.3.3.2).

HasSubtype

0..*

Used to identify subtypes (see 5.3.3.3).

Standard Properties

NodeVersion

O

String

The NodeVersion Propertyis used to indicate the version of a Node.

The NodeVersion Propertyis updated each time a Referenceis added or deleted to the Nodethe Propertybelongs to. Attributevalue changes do not cause the NodeVersionto change. Clientsmay read the NodeVersion Propertyor subscribe to it to determine when the structure of a Nodehas changed.