In message queuing, a message is simply a collection of data sent by one program and intended for another program.
WebSphere MQ defines four types of message:
| Datagram | A simple message for which no reply is expected |
| Request | A message for which a reply is expected |
| Reply | A reply to a request message |
| Report | A message that describes an event such as the occurrence of an error |
See Types of message for more information about these message types.
A WebSphere MQ message consists of control information and application data. The control information is defined in a message descriptor structure (MQMD) and contains such things as:
The structure and content of the application data is determined by the participating programs, not by WebSphere MQ.
A message channel agent moves messages from one queue manager to another. References are made to them in this book when dealing with report messages and you will need to consider them when designing your application. See WebSphere MQ Intercommunication for more information.