To promote interoperability of clients and Servers, the OPC UA AddressSpaceis structured as a hierarchy, with the top levels standardised for all Servers. Figure 1illustrates the structure of the AddressSpace. All Objectsin this figure are organised using Organizes Referencesand have the ObjectType FolderType as type definition.

image004.png

Figure 1– Standard AddressSpace structure

The remainder of this provides descriptions of these standard Nodesand the organization of Nodesbeneath them. Serverstypically implement a subset of these standard Nodes, depending on their capabilities.

This standard Objectis the browse entry point for the AddressSpace. It contains a set of Organizes Referencesthat point to the other standard Objects. The "Root" Objectshall not reference any other NodeClasses. It is formally defined in Table 94.

Table 94– Root definition

Attribute

Value

BrowseName

Root

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

Object

Views

Defined in 8.2.3

Organizes

Object

Objects

Defined in 8.2.4

Organizes

Object

Types

Defined in 8.2.5

Conformance Units

Base Info Core Structure 2

This standard Objectis the browse entry point for Views. Only Organizes Referencesare used to relate View Nodesto the "Views" standard Object. All View Nodesin the AddressSpace shall be referenced by this Node, either directly or indirectly. That is, the "Views" Objectmay reference other Objectsusing Organizes References. Those Objectsmay reference additional Views. Figure 2illustrates the Views organization. The "Views"standard Objectdirectly references the Views"View1" and "View2" and indirectly "View3" by referencing another Objectcalled "Engineering".

image005.png

Figure 2– Views organization

The "Views" Objectshall not reference any other NodeClasses. The "Views" Objectis formally defined in Table 95.

Table 95– Views definition

Attribute

Value

BrowseName

Views

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Conformance Units

Base Info Core Views Folder

This standard Objectis the browse entry point for Object Nodes. Figure 3illustrates the structure beneath this Node. Only Organizes Referencesare used to relate Objectsto the "Objects" standard Object. A View Nodecan be used as entry point into a subset of the AddressSpacecontaining Objectsand Variablesand thus the "Objects" Objectcan also reference View Nodes using Organizes References. The intent of the "Objects" Objectis that all Objectsand Variablesthat are not used for type definitions or other organizational purposes (e.g. organizing the Views) are accessible through hierarchical Referencesstarting from this Node. However, this is not a requirement, because not all Serversmay be able to support this. This Objectreferences the standard Server Objectdefined in 8.3.2.

image006.png

Figure 3– Objects organization

The "Objects" Objectis formally defined in Table 96.

Table 96– Objects definition

Attribute

Value

BrowseName

Objects

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

Object

Server

Defined in 8.3.2

Organizes

Object

Locations

Defined in 8.2.12.

Conformance Units

Base Info Core Structure 2

This standard Object Nodeis the browse entry point for type Nodes. Figure 1illustrates the structure beneath this Node. Only Organizes Referencesare used to relate Objectsto the "Types" standard Object. The "Types" Objectshall not reference any other NodeClasses. It is formally defined in Table 97.

Table 97– Types definition

Attribute

Value

BrowseName

Types

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

Object

ObjectTypes

Defined in 8.2.6

Organizes

Object

VariableTypes

Defined in 8.2.7

Organizes

Object

ReferenceTypes

Defined in 8.2.8

Organizes

Object

DataTypes

Defined in 8.2.9

Organizes

Object

EventTypes

Defined in 8.2.10

Organizes

Object

InterfaceTypes

Defined in 8.2.11

Conformance Units

Base Info Core Types Folders

This standard Object Nodeis the browse entry point for ObjectType Nodes. Figure 4illustrates the structure beneath this Node showing some of the standardObjectTypes defined in Clause 6. Only Organizes Referencesare used to relate Objectsand ObjectTypesto the "ObjectTypes" standard Object. The "ObjectTypes" Objectshall not reference any other NodeClasses.

image007.png

Figure 4– ObjectTypes organization

The intention of the "ObjectTypes" Objectis that all ObjectTypesof the Serverare either directly or indirectly accessible browsing HierarchicalReferencesstarting from this Node. However, this is not required and Serversmight not provide some of their ObjectTypesbecause they may be well-known in the industry, such as the ServerType defined in 6.3.1.

This Objectalso indirectly references the BaseEventTypedefined in 6.4.2, which is the base type of all EventTypes. Thereby it is the entry point for all EventTypesprovided by the Server. It is required that the Serverexpose all its EventTypes, so a client can usefully subscribe to Events.

The "ObjectTypes" Objectis formally defined in Table 98.

Table 98– ObjectTypes definition

Attribute

Value

BrowseName

ObjectTypes

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

ObjectType

BaseObjectType

Defined in 6.2

Conformance Units

Base Info Core Types Folders

This standard Objectis the browse entry point for VariableType Nodes. Figure 5illustrates the structure beneath this Node. Only Organizes Referencesare used to relate Objectsand VariableTypesto the "VariableTypes" standard Object. The "VariableTypes" Objectshall not reference any other NodeClasses.

image008.png

Figure 5– VariableTypes organization

The intent of the "VariableTypes" Objectis that all VariableTypesof the Serverare either directly or indirectly accessible browsing HierarchicalReferencesstarting from this Node. However, this is not required and Serversmight not provide some of their VariableTypes, because they may be well-known in the industry, such as the "BaseVariableType" defined in 7.2.

The "VariableTypes" Objectis formally defined in Table 99.

Table 99– VariableTypes definition

Attribute

Value

BrowseName

VariableTypes

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

VariableType

BaseVariableType

Defined in 7.2

Conformance Units

Base Info Core Types Folders

This standard Objectis the browse entry point for ReferenceType Nodes. Figure 6illustrates the organization of ReferenceTypes. Organizes Referencesare used to define ReferenceTypesand Objectsreferenced by the "ReferenceTypes" Object. The "ReferenceTypes" Objectshall not reference any other NodeClasses. See Clause 11for a discussion of the standard ReferenceTypesthat appear beneath the "ReferenceTypes" Object.

image009.png

Figure 6– ReferenceType definitions

Since ReferenceTypeswill be used as filters in the browse Serviceand in queries, the Servershall provide all its ReferenceTypes, directly or indirectly following hierarchical Referencesstarting from the "ReferenceTypes" Object. This means that, whenever the client follows a Reference, the Servershall expose the type of this Reference in the ReferenceTypehierarchy. It shall provide all ReferenceTypesso that the client would be able, following the inverse subtype of References, to come to the base References ReferenceType. It does not mean that the Servershall expose the ReferenceTypesthat the client has not used any Referenceof.

The "ReferenceTypes" Objectis formally defined in Table 100.

Table 100– ReferenceTypes definition

Attribute

Value

BrowseName

ReferenceTypes

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

ReferenceType

References

Defined in 11.1

Conformance Units

Base Info Core Types Folders

This standard Objectis the browse entry point for DataTypesthat the Serverwishes to expose in the AddressSpace.

DataType Nodesshould be made available using Organizes Referencespointing either directly from the "DataTypes" Objectto the DataType Nodesor using additional Folder Objectsfor grouping purposes. The intent is that all DataTypesof the Serverexposed in the AddressSpaceare accessible following hierarchical Referencesstarting from the "DataTypes" Object. However, this is not required.

The "DataTypes" Objectis formally defined in Table 101.

Table 101– DataTypes definition

Attribute

Value

BrowseName

DataTypes

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

DataType

BaseDataType

Defined in 12.2

Conformance Units

Base Info Core Types Folders

This standard Object Nodeis the browse entry point for EventType Nodes. Figure 7illustrates the structure beneath this Node showing some of the standardEventTypes defined in Clause 6. Only Organizes Referencesare used to relate Objectsand ObjectTypesto the "EventTypes" standard Object. The "EventTypes" Objectshall not reference any other NodeClasses.

image010.png

Figure 7– EventTypes organization

The intention of the "EventTypes" Objectis that all EventTypesof the Serverare either directly or indirectly accessible browsing HierarchicalReferencesstarting from this Node. It is required that the Serverexpose all its EventTypes, so a client can usefully subscribe to Events.

The "EventTypes" Objectis formally defined in Table 102.

Table 102– EventTypes definition

Attribute

Value

BrowseName

EventTypes

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

ObjectType

BaseEventType

Defined in 6.4.2

Conformance Units

Address Space Events 2

This standard Object Nodeis the browse entry point for ObjectType Nodesthat represent Interfaces. Figure 8illustrates the structure beneath this Node showing some of the standardObjectTypes defined in clause 6. Only Organizes Referencesare used to relate Objectsand Interfacesto the “InterfaceTypes” standard Object. The “InterfacesTypesObjectshall not reference any other NodeClasses.

image011.png

Figure 8– InterfaceTypes Organization

The intention of the “InterfaceTypesObjectis that all Interfacesof the Serverare either directly or indirectly accessible browsing HierarchicalReferencesstarting from this Node. However, this is not required and Serversmight not provide some of their Interfacesbecause they may be well-known in the industry.

The “InterfaceTypesObjectis formally defined in Table 103.

Table 103– InterfaceTypes definition

Attribute

Value

BrowseName

InterfaceTypes

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Organizes

ObjectType

BaseInterfaceType

Defined in 6.9

Conformance Units

Address Space Interfaces

This standard Objectis the browse entry point for Object Nodes which represent different types of locations. Figure 9illustrates the structure beneath this Node. Only Organizes Referencesare used to relate Objects.

image012.png

Figure 9– Locations organization

The intent of the "Locations" Objectis an entry point for different types of locations. The types of locations organize locations.

The "Locations" Objectis formally defined in Table 99.

Table 104– Locations definition

Attribute

Value

BrowseName

Locations

References

NodeClass

BrowseName

Comment

HasTypeDefinition

ObjectType

FolderType

Defined in 6.6

Conformance Units

Base Info Locations Object