The SerializedData Variable holds the SerializationValue, customized by the SerializationProperties.
The DataType of the SerializationValue is the SerializationValue DataType and is a subtype of Structure where the DataTypeDefinition Attribute of this DataType provides the metadata and encoding information.
The DataType Node including the DataTypeDefinition Attribute is dynamically created. It only has an inverse Reference to its supertype Structure. Clients must obtain the NodeId by reading the DataType Attribute of the SerializedData Variable. Then they must read the DataTypeDefinition Attribute of the DataType to be able to decode the SerializationValue.
The Value of the SerializedData Variable is only generated (serialized) when requested by the Read Service, by a Subscription or in PubSub publishing.
The SerializationValue is typically read-only. If the Server supports write access, the Client’s Session shall be able to successfully write all original Variables in the SerializationScope. If the write for any Variable fails, the write call shall fail and return a proper result code (e.g., Bad_NotWritable, Bad_InvalidArgument, and Bad_ConfigurationError).
If the SerializationScope contains nested subtrees, each element that has children itself has its own DataType Node describing these direct children of this element.
The SerializationValue can change in the following ways:
- By changing the SerializationProperties with the ConfigureSerialization Method.
- By other changes of the AddressSpace, for instance insertion or deletion of child nodes on any level of the subtree in the SerializationScope.
In case of such changes, a new DataType shall be created with a new DataType NodeId and encoding NodeId. This DataType Attribute of the SerializedData Variable shall refer to this new DataType.
In case of PubSub, a change of the DataType NodeId causes a change of the metadata.
Servers may not be able to save dynamically created Nodes. In addition, the AddressSpace may have changed (reconfigured) during shutdown.
If the SerializationEntity is an InstanceDeclaration, accessing the SerializedData Variable is not possible. Reading attempts are answered with the StatusCode Bad_NoValue.
Note 1: It may be useful to use GUID NodeIds due to the dynamic of the process.
Note 2: It is recommended, that Servers persist DataType NodeIds so that these NodeIds remain in place after restart, if the SerializationScope has not changed.