The term message is used with various intentions in the messaging world. It sometimes only refers to the payload (the application data) and sometimes to the network packet that also includes protocol-, security-, or encoding-specific data. To avoid confusion, this document formally defines the term DataSetMessage  to mean the application data (the payload) supplied by the Publisher and the term NetworkMessage  to mean the message handed off and received from a specific Message Oriented Middleware. DataSetMessages  are embedded in NetworkMessages. Figure 4 shows the relationship of these message types.


Figure 4 – OPC UA PubSub message layers

The transport protocol-specific headers and definitions are described in 7.3.

Subclauses 5.3.2 to 5.3.4 provide an abstract definition of DataSetMessage and NetworkMessage. The concrete structure depends on the message mapping and is described in 7.2.

DataSetMessages are just one of the possible MessageTypes transported within a NetworkMessage. The different MessageTypes are defined in 7.2.