If a DataType Node is exposed in the AddressSpace, it shall provide its DataTypeEncodings using HasEncoding References. These References shall be bi-directional. Figure 19 provides an example how DataTypes are modelled in the AddressSpace.

Figure 19 – Example of DataType Modelling

The information on how to encode the DataType is provided in the Attribute DataTypeDefinition of the DataType Node. The content of this Attribute shall not be changed once it had been provided to Clients since Clients might persistently cache this information. If the encoding of a DataType needs to be changed conceptually a new DataType needs to be provided, meaning that a new NodeId shall be used for the DataType. Since Clients identify the DataType via the DataTypeEncodings, also the NodeIds for the DataTypeEncodings of the DataType shall be changed, when the encoding changes.