Properties are used to define the characteristics of Nodes. Properties are defined using the Variable NodeClass, specified in Table 13. However, they restrict their use.

Properties are the leaf of any hierarchy; therefore they shall not be the SourceNode of any hierarchical References. This includes the HasComponent or HasProperty Reference, that is, Properties do not contain Properties and cannot expose their complex structure. However, they may be the SourceNode of any NonHierarchical References.

The HasTypeDefinition Reference points to the VariableType of the Property. Since Properties are uniquely identified by their BrowseName, all Properties shall point to the PropertyType defined in OPC 10000-5.

Properties shall always be defined in the context of another Node and shall be the TargetNode of at least one HasProperty Reference. To distinguish them from DataVariables, they shall not be the TargetNode of any HasComponent Reference. Thus, a HasProperty Reference pointing to a Variable Node defines this Node as a Property.

The BrowseName of a Property is always unique in the context of a Node. It is not permitted for a Node to refer to two Variables using HasProperty References having the same BrowseName.