Events & Messages
In general terms, an Event, along with Queries and Commands, is a type of message :
Something that has happened that you want to tell others about.
These are typically thought of in terms of streams of updates. For example, pricing streams and trade streams in capital markets are examples of event streams.
Events are always Pub / Sub.
Retrieves information. Think HTTP GET, HEAD.
Queries always carry a response. Within a messaging system they need to be synchronous for requesting applications.
Queries are often point-to-point.
Instructs another app to do something to change the state of something. Think HTTP POST, PUT, DELETE.
Commands, like Queries, always carry a response, and within a messaging system they need to be synchronous for commanding applications.
And also like Queries, Commands are often point-to-point.
Solace PubSub+ supports all 3 types of messages in either synch or async from a sender, and either persistent or non-persistent QoS.