Nodesand their Referencesto each other are illustrated using figures. Figure 1illustrates the conventions used in these figures.


Figure 1– AddressSpace Node diagrams

In these figures, rectangles represent Nodes. Noderectangles may be titled with one or two lines of text. When two lines are used, the first text line in the rectangle identifies the NodeClassand the second line contains the BrowseName. When one line is used, it contains the BrowseName.

Noderectangles may contain boxes used to define their Attributesand References. Specific names in these boxes identify specific Attributesand References.

Shaded rectangles with rounded corners and with arrows passing through them represent References. The arrow that passes through them begins at the SourceNodeand points to the TargetNode. Referencesmay also be shown by drawing an arrow that starts at the Referencename in the “References” box and ends at the TargetNode.

Clause 4.9defines AddressSpace NodeClasses. Table 1describes the format of the tables used to define NodeClasses.

Table 1– NodeClass Table Conventions



Data Type



“Attribute name”

“M” or “O”

Data type of the Attribute

Defines the Attribute


“Reference name”

“1”, “0..1” or “0..*”

Not used

Describes the use of the Referenceby the NodeClass

Standard Properties

“Property name”

“M” or “O”

Data type of the Property

Defines the Property

The Name column contains the name of the Attribute, the name of the ReferenceTypeused to create a Referenceor the name of a Propertyreferenced using the HasProperty Reference.

The Use column defines whether the Attributeor Propertyis mandatory (M) or optional (O). When mandatory the Attributeor Propertyshall exist for every Nodeof the NodeClass. For Referencesit specifies the cardinality. The following values may apply:

  • “0..*” identifies that there are no restrictions, that is, the Referencedoes not have to be provided but there is no limitation how often it can be provided;
  • “0..1” identifies that the Referenceis provided at most once;
  • “1” identifies that the Referenceshall be provided exactly once.

The Data Type column contains the name of the DataTypeof the Attributeor Property. It is not used for References.

The Description column contains the description of the Attribute, the Referenceor the Property.

Only this document may define Attributes. Thus, all Attributesof the NodeClassare specified in the table and may only be extended by other parts of this series of standards.

This document also defines ReferenceTypes, but ReferenceTypesmay also be specified by a Serveror by a client using the NodeManagement Servicesspecified in OPC 10000-4. Thus, the NodeClasstables contained in this document may contain the base ReferenceTypecalled Referencesidentifying that any ReferenceTypemay be used for the NodeClass, including system specific ReferenceTypes. The NodeClasstables only specify how the NodeClassescan be used as SourceNodesof References, not as TargetNodes. If a NodeClasstable allows a ReferenceTypefor its NodeClassto be used as SourceNode, this is also true for subtypes of the ReferenceType. However, subtypes of the ReferenceTypemay restrict its SourceNodes.

This document defines Properties, but Propertiescan be defined by other standard organizations or vendors and Nodescan have Propertiesthat are not standardised. Propertiesdefined in this standard are defined by their name, which is mapped to the BrowseNamehaving the NamespaceIndex0, which represents the Namespacefor OPC UA.

The Use column (optional or mandatory) does not imply a specific ModellingRulefor Properties. Different Serverimplementations will choose to use ModellingRulesappropriate for them.