Understanding PubSub messages

The basic building block of the PubSub system is the PubSub message. All messages contain a topic name that uniquely identifies the data of interest. The rest of the message depends on whether it is a subscription or a publication.

Only publication messages contain a data payload. The data payload is empty for all other messages. A data payload contains one or more simple items, such as strings or numbers. Typical publications have only one item in the payload, but some will contain a more complex payload. Publication messages also include routing and security data.

The following examples detail typical PubSub Data Payload messages:

Whether the payload is simple or complex, the publisher and the subscribers must agree on the type and order of data items. This contract should remain consistent from one publication to the next, as well as from one release to the next. Any change to a data payload must be designed very carefully to ensure that it is both forward and backward compatible.

For information on handling PubSub messages, refer to the AVEVA Enterprise SCADA PubSub Application Programming Interface (API) Reference documentation.