Nodes and their References to each other are illustrated using figures. Figure 1 illustrates the conventions used in these figures.


Figure 1 – AddressSpace Node diagrams

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

Node rectangles may contain boxes used to define their Attributes and References. Specific names in these boxes identify specific Attributes and References.

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

Clause 4.10 defines AddressSpace NodeClasses. Table 1 describes 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 Reference by 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 ReferenceType used to create a Reference or the name of a Property referenced using the HasProperty Reference.

The Use column defines whether the Attribute or Property is mandatory (M) or optional (O). When mandatory the Attribute or Property shall exist for every Node of the NodeClass. For References it specifies the cardinality. The following values may apply:

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

The Data Type column contains the name of the DataType of the Attribute or Property. It is not used for References.

The Description column contains the description of the Attribute, the Reference or the Property.

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

This document also defines ReferenceTypes, but ReferenceTypes may also be specified by a Server or by a client using the NodeManagement Services specified in OPC 10000-4. Thus, the NodeClass tables contained in this document may contain the base ReferenceType called References identifying that any ReferenceType may be used for the NodeClass, including system specific ReferenceTypes. The NodeClass tables only specify how the NodeClasses can be used as SourceNodes of References, not as TargetNodes. If a NodeClass table allows a ReferenceType for its NodeClass to be used as SourceNode, this is also true for subtypes of the ReferenceType. However, subtypes of the ReferenceType may restrict its SourceNodes.

This document defines Properties, but Properties can be defined by other standard organizations or vendors and Nodes can have Properties that are not standardised. Properties defined in this standard are defined by their name, which is mapped to the BrowseName having the NamespaceIndex 0, which represents the Namespace for OPC UA.

The Use column (optional or mandatory) does not imply a specific ModellingRule for Properties. Different Server implementations will choose to use ModellingRules appropriate for them.