In line with the Symbolic Systems paradigm, events are best understood in terms of interactions between systems (or enterprises) and the environment they represent (or live off).
On that account events are to be associated with four kinds of notifications:
- Actual (aka non symbolic) changes in the state of objects.
- Actual (aka non symbolic) changes in the state of activities.
- Changes in the state of expectations (e.g requests/acknowledgments).
- Neutral changes in symbolic representations (e.g messages).
It must be noted that while synchronization constraints (e.g UML’s calls vs signals) characterize events’ communication semantics, they say nothing about events themselves.
That distinction is of a particular importance for the definition of time as a
change in a dedicated physical device, ensuring that, according to Einstein, events don’t happen at once.