This article by Alex Alves discusses message types in Domain-Driven Design. A message can be any intention of transmitting and/or processing information, regardless of the way it is produced and consumed. The article then identifies different types of messages, including command messages which invoke functionality in another application, event messages which represent business facts triggered by commands, integration events which are produced by external agents and notify when something happens, notification events which just have an ID and notify all interested parties, and query messages which retrieve data from our system. The article concludes by emphasizing the importance of identifying message intention and directing each message to a specific channel. References to message broker and async request-reply pattern are also provided.
