The structured data type is a record or a representation of union (in data dictionary model, i.e. the only model available before OPC UA 1.04). It is represented by an instance of the StructuredDataType Class.

The DataFields Property contains a collection of data fields of the structured data type. Each such data field is an instance of DataField Class, and specifies:

• A DataType of the contents of the field.
• A Name: Data field name, unique within the structured data type.
• A Description: Human readable description of the data field.
• An IsLength flag: Determines whether the field denotes a length of some sequence. Length fields may have special behavior e.g. with respect to Generic data auto-complete, and in validation of generic data (see Generic data validation).
• An IsOptional flag: Determines whether the field can be omitted from the encoded data. Optional fields play role in determining whether a recursive data type is terminable (see Working with data types) and in validation of generic data (see Generic data validation).
• An IsSwitch flag: Determines whether the field acts as a switch for some other field. Switch fields may have special behavior e.g. with respect to Generic data auto-complete.

The StructuredDataType Class is an IEnumerable of DataField, and it has an Add Method for the same. It means that you can easily enumerate through its data fields, and it can also participate in collection initializers in C# or in VB.NET.