OPC UA defines a graphical notation for an OPC UA AddressSpace. It defines graphical symbols for all NodeClasses and how different types of References between Nodes can be visualised. Figure 3 shows the symbols for the six NodeClasses used in this specification. NodeClasses representing types always have a shadow.
Figure 3 – OPC UA graphical notation for NodeClasses
Figure 4 shows the symbols for the ReferenceTypes used in this specification. The Reference symbol is normally pointing from the source Node to the target Node. The only exception is the HasSubtype Reference. The most important References like HasComponent, HasProperty, HasTypeDefinition and HasSubtype have special symbols avoiding the name of the Reference. For other ReferenceTypes or derived ReferenceTypes the name of the ReferenceType is used together with the symbol.
Figure 4 – OPC UA graphical notation for References
Figure 5 shows a typical example for the use of the graphical notation. Object_A and Object_B are instances of the ObjectType_Y indicated by the HasTypeDefinition References. The ObjectType_Y is derived from ObjectType_X indicated by the HasSubtype Reference. The Object_A has the components Variable_1, Variable_2 and Method_1.
To describe the components of an Object on the ObjectType the same NodeClasses and References are used on the Object and on the ObjectType like for ObjectType_Y in the example. The instance Nodes used to describe an ObjectType are instance declaration Nodes.
To provide more detailed information for a Node, a subset or all Attributes and their values can be added to a graphical symbol.
Figure 5 – OPC UA graphical notation example