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 27.

Table 27 – 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).