An example of a UML class representing the OPC UA concept Base is given in the UML class diagram in Figure B.2. OPC Attributes inherit from the abstract class Attribute and have a value identifying their data type. They are composed of a Node which is either optional (0..1) or required (1), such as BrowseName to Base in Figure B.2.
Figure B.2 – Notation (I)
UML object diagrams are used to display <<TypeExtension>> objects (e.g. HasComponent in Figure B.3). In object diagrams, OPC Attributes are represented as UML attributes without data types and marked with the stereotype <<Attribute>>, like InverseName in the UML object HasComponent. They have values, like InverseName =ComponentOf for HasComponent. To keep the object diagrams simple, not all Attributes are shown (e.g. the NodeId of HasComponent).
Figure B.3 – Notation (II)
OPC References are represented as UML associations marked with the stereotype <<Reference>>. If a particular ReferenceType is used, its name is used as the role name, identifying the direction of the Reference (e.g. Aggregates has the subtype HasComponent). For simplicity, the inverse role name is not shown (in the example SubtypeOf). When no role name is provided, it means that any ReferenceType can be used (only valid for class diagrams).
There are some special Attributes in OPC UA containing a NodeId and thereby referencing another Node. Those Attributes are represented as associations marked with the stereotype <<Attribute>>. The name of the Attribute is displayed as the role name of the TargetNode.
The value of the OPC Attribute BrowseName is represented by the UML object name, for example the BrowseName of the UML object HasComponent in Figure B.3 is “HasComponent”.
To highlight the classes explained in a class diagram, they are marked in grey (e.g. Base in Figure B.2). Only those classes have all of their relationships to other classes and attributes shown in the diagram. For the other classes, we provide only those attributes and relationships needed to understand the main classes of the diagram.