What type of messaging primitive does NOT change the system state?

Queries are designed to retrieve data or information without altering the current state of the system. They operate under the principle of "read-only," meaning that executing a query does not produce side effects that modify the database or system state. Instead, queries generate a response that reflects the existing state at the time of the request.

On the other hand, commands are intended to perform actions that will lead to changes in the state of the system, such as creating, updating, or deleting records. Events signal that something has occurred and can often indicate a state change, making them relevant in tracking system state over time. Responses are generated in reaction to requests but can be part of a process initiated by commands or queries.