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What is an actor in OSC2?

After clarification what an action is and that an action is always bound to an actor, we came to the issue of defining (or revisiting the definition) what an actor is.

Here is my proposal:

An actor is everything that can take an active role in a scenario, i.e. everything that usually moves, commits actions or changes its state ain a perceivable and meaningful way (for short, any object that is "active"). Actors can be physical objects in the scenario, but in some cases also abstract objects or objects outside of the scenario.

Actors can be divided into the following subclasses:

  1. Moving (or dynamic) physical objects in a scenario, like all sorts of vehicles or pedestrians, even if they are temporarily not moving (e.g. a car waiting at a traffic signal; but not a parked car). This is in particular applicable to the ego or subject vehicle or vehicle under test. For human-operated vehicles, it is up to the modeler whether the vehicle or the human are the actor (usually not both of them), e.g. car preferred over car driver, cyclist preferred over bicycle.
  2. Physical objects in a scenario that are stationary, but active in the sense that they commit actions or exhibit a time-varying perceivable state, like traffic lights or barriers at a railroad crossing.
  3. Physical objects that are normally static and passive, but exceptionally take the role of an actor in a particular scenario, like a plastic bag blowing in the wind, a trash bin moving across the street during a hurricane, an exploding gas tank.
  4. Parts of the environment or phenomena and structures in a scenario if they commit actions or exhibit a perceivable and time-variant state of relevance, e.g. the sky (that can change from clear to cloudy), the weather (e.g. "It's starting to rain" is an action), the road when it is icing, a bridge when it is trembling.
  5. In case of scenarios in a simulation or test setting: Objects and phenomena outside the simulated scenario that have an influence on the scenario, in particular the test bed and parts of it, e.g. a probe or failure-injection device, a script that replays a scenario, an emergency stop button on the test vehicle's dashboard, the human operator of a test stand

Any actor can be the subject of an action. An action without an actor is not possible.