Usually it is desirable to expose some information on the inner state of the machine vision framework to the outside world. A state machine only covers information on the current control state of the vision system. If an error occurs it transits to the Error state, but offers no information why this happened. Therefore we need additional communication elements that are capable of transporting error messages, warning messages to avoid the occurrence of an error, or any other kind of information helpful for the client.
The kind of errors that may occur and the additional information to be transported are highly application specific. Therefore it is out of scope for this standard to define such things. Instead we are defining a framework of rules on how to structure application specific messages and how messages should interact with the state machine. The goal for this is to make it possible that even a “generic” client without further knowledge of a specific application is able to get a basic picture of the current state of the vision system.