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Methods

Defining Object Methods in the Sterfive OPCUA Modeler YAML File​

Methods in OPC UA are defined operations that are part of an Object or ObjectType node. They provide a way to define actions that can be executed, typically involving the object's variables. Methods in Sterfive OPCUA Modeler are defined within the methods section of an objectTypes element in the YAML file.

Let's explore the structure in detail:

Method Structure:​

objectTypes:
  - browseName: MyObjectType
    methods:
      - browseName: AddTwoValues
        inputArguments:
          - name: Operand1
            dataType: ua:Double
            description: The value of operand 1
          - name: Operand2
            dataType: ua:Double
            description: The value of operand 2
        outputArguments:
          - name: Result
            dataType: ua:Double
            description: The result of the operation

Here, a method AddTwoValues is defined under an object type MyObjectType.

The browseName attribute of a method represents the method's normative name in the OPC UA node. This is used by OPC UA clients to browse through the tree of nodes via their access path. A node's path within the tree is made up of browseNames.

Methods can have inputArguments and outputArguments, which are defined as lists. Each argument in the list has a name, dataType, and description.

The inputArguments section defines the inputs that the method requires, with each argument having a name, dataType (e.g., ua:Double), and description. ua:Double means the argument is a floating-point number defined in the OPC UA namespace.

The outputArguments section describes the values returned by the method after execution. Like inputArguments, each outputArguments item includes a name, dataType, and description. If the method does not return any value, this section can be omitted.

Methods can return multiple values, and in such a case, the outputArguments section will have multiple elements.

Here's an example of a method returning multiple values:

objectTypes:
  - browseName: MyObjectType
    methods:
      - browseName: CalculateMeanAndStandardDeviation
        inputArguments:
          - name: ArrayOfValue
            dataType: ua:Double
            valueRank: 1
            description: an array containing the values to transform
        outputArguments:
          - name: Mean
            dataType: ua:Double
            description: The mean value of the array
          - name: StandardDeviation
            dataType: ua:Double
            description: The standard deviation value of the array

In this example, the CalculateMeanAndStandardDeviation method takes an array of doubles as input and returns two output values: the Mean and Standard Deviation of the array.

By defining methods in this way, users can outline various operations related to an ObjectType, providing a flexible and robust means to interact with objects in the OPC UA model.