VariableRefs and RecordItemRefs can define Buttons. Those IODD Buttons are mapped to OPC UA Methods.

For each Button-defining VariableRef or RecordItemRef from an IODD Menu that is used in the mapping (see section 7.3.5) an OPC UA Method is created, that is referenced with a HasComponent Reference from the MethodSet Object.

In case several VariableRefs or RecordItemRefs have the same characteristics (Description, ActionStartedMessage, buttonValue, and in case of RecordItemRefs same subindex), only one Method is created.

The Objects representing the IODD Menus shall reference the corresponding Methods with Organizes References.

If at least one Object representing an IODD Menu referencing the Method has the ModellingRule Mandatory the Method shall have the ModellingRule Mandatory, otherwise Optional.

The BrowseName of the Method shall be the Id of the IODD Variable combined with the buttonValue. The format is “<Id>|<buttonValue>”. In the unlikely case that the IODD Variable is referenced several times as Button with the same buttonValue but different other characteristics (Description and ActionStartedMessage), the additional Methods have a BrowseName postfixed by a number using the format “<Id>|<buttonValue>_<n>” where “n” is the occurrence in the order of the IODD, starting with a 2 for the second occurrence.

The DisplayName shall be the Description of the IODD Button, if a Description is provided. Localization should be considered. If no Description is provided, the DisplayName should be the BrowseName. The optional Description Attribute is vendor-specific and might be omitted.

The Methods shall not have input- or output-arguments. If the optional ActionStartedMessage of the IODD Button is provided, there shall be a Property with BrowseName “ActionStartedMessage” and the DataType String, providing the ActionStartedMessage of the IODD Button.

Note: The way a button is modelled inside an IODD VariableRef element changed from IODD Specification Version 1.0.1 to Version 1.1. The information modelled in IODD Specification Version 1.1 in the elements Description and ActionStartedMessage is not provided in IODD Specification Version 1.0.1.

The server-internal implementation of the Method shall implement the IODD Button according to the IODD Specification.

An example on how to map IODD Buttons to OPC UA Methods is shown in Figure 18.


Figure 18 – Example on how to map IODD Buttons to OPC UA Methods