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5.3 OPC UA XML ToC Previous Next

5.3.3 Enumerations ToC Previous Next

Enumerations that are used as parameters in the Messages defined in OPC 10000-4 are encoded as xs:string with the following syntax:

<symbol>_<value>

The elements of the syntax are described in Table 22.

Table 22 – Components of Enumeration

Field Type Description
<symbol> String The symbolic name for the enumerated value.
<value> UInt32 The numeric value associated with enumerated value.

For example, the XML schema for the NodeClass enumeration is:

<xs:simpleType name="NodeClass">
<xs:restriction base="xs:string">
<xs:enumeration value="Unspecified_0" />
<xs:enumeration value="Object_1" />
<xs:enumeration value="Variable_2" />
<xs:enumeration value="Method_4" />
<xs:enumeration value="ObjectType_8" />
<xs:enumeration value="VariableType_16" />
<xs:enumeration value="ReferenceType_32" />
<xs:enumeration value="DataType_64" />
<xs:enumeration value="View_128" />
</xs:restriction>
</xs:simpleType>

Enumerations that are stored in a Variant are encoded as an Int32 value.

For example, any Variable could have a value with a DataType of NodeClass. In this case, the corresponding numeric value is placed in the Variant (e.g. NodeClass Object would be stored as a 1).

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